Forecasts

Thursday in Thornton remains warm, will see more clouds, a slight chance for precipitation

A little bit of a change up in the ongoing weather pattern is in store for us today. Moisture has increased and while it will bring some clouds, any precipitation we see will be light.

Mostly cloudy to cloudy skies will above throughout the daytime hours today. Conditions will be calm this morning and in the early afternoon. Mid to late afternoon could see a few sprinkles of rain. Highs will top out in the mid-70s.

This evening, chances for precipitation increase, maybe bringing a brief, light shower. Any amounts are currently expected to be minimal. It will remain mostly cloudy overnight, maybe with a few drops of rain. Lows will beMore: https://www.thorntonweather.com/

Weather History

October 18 to October 24: This week in Denver weather history

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This Week in Denver Weather History

This week is an extremely eventful one in Denver weather history with a wide variety of conditions having been experienced in the past. Wind and snow are probably the two most dominant items, none more so than the blizzard that struck 23 years ago on the 24th. That storm ravaged the city, closed the airport and highways and was responsible for four deaths.

From the National Weather Service:

From the 17th to the 19th:

In 1908…a moist…heavy…wet snowfall totaled 13.0 inches in downtown Denver over the 3 days. Rain from early morning on the 17th changed to snow by late afternoon and continued through the late morning of the 19th. Due to temperatures in the 30’s and melting…the most snow on the ground was only 5.0 inches at 6:00 pm on the 18th. Northwest to northeast winds were sustained between 12 and 20 mph during the storm. Precipitation totaled 1.82 inches.

On the 18th:

In 1875…the haze was so dense that the mountains were not visible from downtown Denver for most of the day.

In 1937…a vigorous cold front produced north winds sustained to 32 mph with gusts to 41 mph. Rain and snow totaled 0.16 inch. Post-frontal snowfall of 0.8 inch was the only snowfall of the month.

In 1960…post-frontal upslope rain changed to snow. Snowfall was 2.2 inches at Stapleton Airport where precipitation (rain and melted snow) totaled 1.58 inches.

In 1971…wind gusts to 48 mph were recorded in downtown Boulder. West winds gusted to 30 mph at Stapleton International Airport.

In 1999…heavy snow developed in the foothills west of metro Denver with lesser amounts across the city. Snowfall totals included: 7 inches near Nederland…6 inches in Boulder…and 5 inches at Chief Hosa. Only 1.2 inches of snow were measured at the site of the former Stapleton International Airport.

From the 18th to the 23rd:

In 2003…an extended warm spell resulted in 5 new temperature records. The high temperature of 84 degrees on the 18th equaled the record high for the date. High temperatures of 86 degrees on the 19th…83 degrees on the 21st…and 84 degrees on the 22nd were record highs for the dates. Low temperature of 49 degrees on the 23rd was a record high minimum for the date. Low temperatures during the period were in the 40’s and lower 50’s.

On the 19th:

In 1887…northwest winds sustained to 42 mph were recorded in the city.

In 1982…3 to 6 inches of snow fell over northwest metro Denver…including Boulder. Only 1.2 inches of snowfall were recorded at Stapleton International Airport where north winds gusted to 35 mph. This was the first measurable snowfall of the season.

From the 19th to the 20th:

In 1990…an early winter storm dumped heavy snow across metro Denver. Snowfall amounts ranged from 4 to 8 inches in the foothills above 6500 feet elevation…4 to 7 inches in the Castle Rock area…and 2 to 5 inches across most of metro Denver and Boulder. Snowfall totaled 3.6 inches at Stapleton International Airport where northwest winds gusting to 48 mph kicked up some blowing dust shortly after a cold frontal passage on the 19th. However… Temperatures were warm enough to keep most roadways wet and slushy at lower elevations.

From the 19th to the 23rd:

In 1906…heavy snowfall totaled 22.7 inches in the city over the 5 days. Rain changed to snow on the evening of the 19th…and snow continued through the late afternoon of the 23rd. The heaviest amount of snowfall…16.0 inches…fell from 8:00 pm on the 20th to 8:00 pm on the 22nd. The most snow on the ground was 13.3 inches on the evening of the 23rd. This was the first snow of the season and the only snow of the month. Winds during the storm were from the north at sustained speeds of 20 to 30 mph each day. Temperatures during the storm were generally in the 20’s.

On the 20th:

In 1878…between 3:00 pm and 4:00 pm wind speeds averaged 48 mph with a maximum 1 minute sustained velocity to 96 mph at both 3:27 pm and 3:48 pm in downtown Denver. This is the highest sustained wind speed ever recorded in the city.

In 1986…a rare late October thunderstorm produced 3/4 inch diameter hail at Centennial Airport. Hail piled up 2 1/2 inches deep…causing some street flooding in south metro Denver.

In 2019…strong bora winds swept across the foothills and adjacent plains. Peak gusts included: 82 mph…3 miles southwest of Rocky Flats; 78 mph near White Ranch Open Space; 75 mph near Genesee and Georgetown; with 63 mph at Firestone. At Denver International Airport…a peak gust of 49 mph was observed from the west.

From the 20th to the 21st:

In 2007…a storm system brought heavy snow to the southern Denver suburbs as well as the Palmer Divide south of Denver. Storm totals included: 7.5 inches near Castle Rock…Lone Tree and Greenwood Village…with 6.5 inches at Elizabeth. Snow drifts up to 2 feet deep were observed 6 miles south-southwest of Elizabeth. In the Denver Stapleton area…2.0 inches of snow was observed.

In 2009…heavy snow developed along the Palmer Divide south and southeast of Denver as a storm system tracked across southern Colorado and northern New Mexico. Storm totals included: 15 inches…15 miles north of Elizabeth…9 inches… 5 miles south-southwest of Arapahoe Park; 8 inches in Highlands Ranch…5 miles south- southeast of Sedalia; 6.5 inches…8 miles southwest of Bennett and 6 inches in Parker. At Denver international… Only 1.5 inches of snowfall was observed.

From the 20th to the 22nd:

In 1936…5.5 inches of snow fell over downtown Denver. Most of the snow…4.5 inches…fell on the 20th.

On the 21st:

In 1920…the rare event of snow from a thunderstorm occurred in the city during the evening. Brilliant flashes of lightning and loud peals of thunder were first noted at 7:35 pm. Light rain began falling at 8:30 pm…and light moist snow began falling a few minutes later. Some soft hail was also seen falling with the rain and snow…but both melted almost as fast as they fell. The hail only continued for a few minutes…and the rain and snow ceased about 9:40 pm. The snowfall was the first to occur in Denver this season. The amount of precipitation at the station measured only 0.01 inch…but heavier amounts were reported from other parts of the city. Snowfall was only a trace.

From the 21st to the 22nd:

In 1978…heavy rain on the 21st changed to snow by daybreak on the 22nd and continued the rest of the day. This was the first measurable snowfall of the season…but totaled only 1.7 inches at Stapleton International Airport where east winds gusted to 29 mph. While only a trace of snow covered the ground…precipitation totaled 1.27 inches.

On the 22nd:

In 1878…winds were sustained to 42 mph.

In 1887…the first measurable snow of the season occurred… Ending the longest snow-free period in Denver…232 days… Since the last snow on march 5th.

In 1947…the first snow of the season totaled only 1.6 inches. Post-frontal north winds caused temperatures to plunge from a high of 60 degrees at midnight to a low of only 30 degrees 24 hours later. This was the only snow of the month.

In 1985…high winds gusting from 60 to 80 mph buffeted the Front Range foothills. The strongest reported wind gust was 89 mph in eastern Boulder. A treehouse east of Boulder was set on fire by a downed power line. Two people in Boulder were injured. A woman broke her arm when the strong winds knocked her to the ground. A carpenter in the city suffered a severely cut hand while he was trying to repair a roof that was being torn from a building. At Stapleton International Airport…northwest winds gusted to 41 mph.

In 2001…west-northwest winds gusting as high as 54 mph warmed the temperature to a high of 70 degrees at Denver International Airport.

Continue reading October 18 to October 24: This week in Denver weather history →

Weather History

October 11 to October 17: This week in Denver weather history

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This Week in Denver Weather History

A very eventful week of weather in Denver weather history. Many notable items have occurred and many also incorporate one of two conditions – wind or snow. Probably the most famous event was the Bronco Blizzard on October 15, 1984. That storm which hit its height during a Monday Night Football game between the Broncos and the Packers is probably one of the most memorable ever for longtime Denver residents.

From the National Weather Service:

10-11

In 1986…the first significant snowstorm of the season produced 2 to 5 inches of snow over metro Denver with 5 to 10 inches in the foothills west of Denver. Wondervu recorded the most snow from the storm…13 inches. The heavy wet snow caused numerous power outages. The storm was accompanied by strong north winds with gusts to 41 mph recorded on the 10th. The first snowfall of the season totaled 3.1 inches at Stapleton International Airport with only one inch on the ground due to melting. The strong cold front accompanying the storm cooled the temperature from a high of 73 degrees on the 10th to a high of only 33 degrees on the 11th…which was a record low maximum for the date.

10-12

In 1969…the second heavy snowstorm in less than a week dumped nearly a foot of snow across metro Denver and plunged the area into extremely cold temperatures for so early in the season. Snowfall totaled 11.0 inches at Stapleton International Airport. North winds gusting to 26 mph produced drifts up to 2 feet deep. Temperatures dipped from a high of 52 degrees on the 10th to a record low for the date of 10 degrees on the 12th. There was additional damage to trees and power and telephone lines from heavy snow accumulations and icing. Travel was restricted or blocked by drifting snow in both the mountains and on the plains east of Denver.

11

In 1997…damaging winds ahead of an approaching storm system developed in the foothills and spread across metro Denver. Winds gusted to 88 mph at Conifer…71 mph at the National Center for Atmospheric Research on the mesa in Boulder… And 53 mph at Denver International Airport. Several trees and street signs were blown down with scattered power outages reported throughout metro Denver. In Arvada…a car window was blown out by a strong wind gust.

In 2013…high winds occurred in and near the Front Range foothills. Peak gusts included: 85 mph at Rooney Road… 84 mph…2 miles south of Marshall; 82 mph at Rocky Flats National Wind Technology Center and Wondervu; 79 mph at the mesa lab at NCAR and 75 mph…3 miles south-southwest of Boulder; 73 mph in superior and 68 mph in Golden. The wind downed trees and power lines. As a result…scattered electrical outages affected 20000 xcel energy customers through the morning hours. The main outages affected the cities of Boulder…Golden and Lakewood. Smaller outages were reported in areas of Gold Hill…Ward… Westminster and Wheat Ridge.

11-12

In 1901…an apparent cold front produced northeast winds sustained to 42 mph with gusts to 48 mph on the 11th. General rain changed to snow overnight and totaled 2.0 inches. This was the first snowfall of the season. Total precipitation was 0.32 inch.

11-13

In 1892…apparent post-frontal rainfall totaled 3.33 inches in downtown Denver over the 3 days. A trace of snow on the 12th melted as it fell. Rainfall of 2.58 inches on the 12th into the 13th was the greatest 24-hour precipitation ever recorded during the month of October. Northwest winds were sustained to 48 mph with gusts as high as 55 mph on the 12th.

12

In 1873…smoke from several very large forest fires was sighted along the mountains.

In 1923…post-frontal rain changed to snow and totaled 4.0 inches. North winds were sustained to 14 mph.

In 1978…northeast winds gusting to 35 mph with a strong cold front briefly reduced visibility to 2 miles in blowing dust at Stapleton International Airport.

12-13

In 2001…overnight peak wind gusts to 82 mph and 70 mph were measured atop Niwot Ridge and Squaw Mountain… Respectively.

12-14

In 1969…record breaking extremely cold temperatures for so early in the season occurred. The high temperature of 26 degrees on the 13th was two degrees lower than the previous record minimum temperature of 28 degrees for the date set in 1885. The high temperature of 24 degrees on the 12th exceeded the record low temperature (22 degrees set in 1885) for the date by only 2 degrees. In addition… 3 new record low temperatures for the dates were set. The low temperature dipped to 10 degrees on the 12th breaking the old record (22 degrees in 1885) by 12 degrees. On the 13th the mercury plunged to a low of 3 degrees breaking the old record (28 degrees in 1885) by 25 degrees. On the 14th the temperature reached a minimum of 4 degrees breaking the old record (25 degrees in 1966) by 21 degrees.

13

In 1990…strong downslope winds stirred up clouds of dust and gravel…rattled windows…and stripped autumn-colored leaves from trees in Boulder. A wind gust to 78 mph was clocked in southwest Boulder…while a 96 mph gust was recorded in northwest Boulder. West winds gusted to only 36 mph at Stapleton International Airport.

13-14

In 1910…light smoke from nearby forest fires drifted over the city.

In 1966…the first measurable snow of the season caused widespread damage to trees and shrubs. The heavy wet snow totaled 6.9 inches at Stapleton International Airport where north-northwest winds sustained at 20 to 25 mph and gusting to 45 mph caused much blowing and drifting snow. South and east of Denver…up to a foot of snow fell. Heavy wet snow accumulations followed by freezing temperatures and strong winds resulted in extensive damage to trees…cars… And utility lines by falling limbs. A woman was killed by a falling snow laden tree limb in Denver. Several other people received minor injuries from falling tree limbs.

In 1987…rain drenched metro Denver. The South Platte Canyon area southwest of Denver received the most with 1.11 inches at Kassler and 1.49 inches upstream at Strontia Springs. At Stapleton International Airport…0.62 inch of rain was measured…northwest winds gusted to 29 mph…and thunder was heard.

In 2007…a new 24-hour record of 2.65 inches of precipitation was set at Denver International Airport for the month of October; breaking the previous record of 2.58 inches set in 1892.

13-16

In 1873…smoke from several large forest fires in the mountains made the air very hazy in the city.

14

In 1952…the first measurable snowfall of the season left 1.2 inches of snow at Stapleton Airport. North winds gusted to 38 mph.

In 1974…rain changed to snow early in the day…but snowfall totaled only 1.0 inch at Stapleton International Airport where northeast winds gusted to 20 mph.

In 2021…very strong wind gusts developed over the higher mountain areas. Peak wind gusts atop Berthoud Pass ranged from 90 to 104 mph. At Denver International Airport…a peak wind gust to 41 mph was observed from the northwest.

15

In 1871…a terrible wind occurred during a snow storm in the foothills above Boulder. Damage was minor.

In 1878…high winds reached sustained speeds of 60 mph at times.

In 1911…post-frontal northwest winds were sustained to 41 mph with gusts to 43 mph.

In 1948…strong winds struck the Boulder area. Winds averaged 50 mph at valmont just east of Boulder. Wind gusts in excess of 60 mph were recorded at the Boulder airport. Wind gusts to 40 mph briefly reduced the visibility to 1 1/2 miles in blowing dust at Stapleton Airport.

In 1980…a rare October tornado touched down in Boulder… Damaging a vocational training building and throwing three nearby cars together damaging them extensively. A mile and half away several camper vehicles were thrown 200 feet. The storm also produced 1 inch diameter hail in the Boulder area.

15-16

In 1928…a thunderstorm produced hail shortly after midnight on the 15th. Rain changed to snow by evening. Through the afternoon of the 16th…the heavy snowfall totaled 7.3 inches in the city. North winds were sustained to 23 mph on the 15th.

In 1984…the heaviest October snowstorm in several years hit eastern Colorado with a vengeance. The storm was known as the “Bronco Blizzard” since it occurred during a nationally televised Monday night football game in Denver. One to two feet of snow fell near the foothills in west metro Denver with 2 to 3 feet in the foothills. Wind gusts up to 55 mph whipped the snow into drifts as high as 4 feet. The storm closed schools…roads…and airports. I-70 was closed both east and west of Denver. I-25 was closed south to Colorado Springs. Flights were delayed for several hours at Stapleton International Airport. Power outages were widespread. Snowfall totaled 9.2 inches at Stapleton International Airport where north winds gusting as high as 40 mph caused frequent surface visibilities of 1/4 to 1/2 mile in moderate to heavy snow and blowing snow overnight. The high temperature of only 35 degrees on the 15th was a record low maximum for the date.

15-17

In 1989…an autumn snowstorm hit metro Denver with 2 to 6 inches of snow. Snowfall totaled 4.4 inches at Stapleton International Airport where the maximum snow depth on the ground was only 3 inches due to melting and north winds gusted to 25 mph on the 15th. The heavy wet snow caused leafy branches to sag onto power lines…resulting in a number of power outages. Five thousand homes were blacked out in Boulder on the 16th. Up to a foot of snow fell in the higher foothills with 19 inches recorded at Echo Lake.

16

In 1878…high winds reached sustained speeds of 60 mph.

In 1998…one of the costliest hail storms to ever hit metro Denver caused an estimated total of 87.8 million dollars in damage to homes…commercial buildings…and motor vehicles. At the time the storm was ranked as the 7th costliest ever. The hailstorm…rare for so late in the season…began over portions of Arvada…Wheat Ridge…and northwest Denver where mostly pea sized hail accumulated up to a depth of 6 inches near I-70. Several accidents were attributed… At least in part…to the hailstorm. Snowplows had to be called out to clear several city streets. The storm intensified as it moved to the east…into the Denver and Aurora areas. Large hail…up to 2.00 inches in diameter pounded east and southeast metro Denver. Two inch diameter hail fell in the city of Denver and at Buckley Field. Hail as large as 1 1/2 inches was measured in south Denver with 1 inch diameter hail in northern Aurora.

In 1999…upslope conditions produced snow across metro Denver with heavy amounts in the nearby foothills. Snowfall totals included: 9 inches at Eldorado Springs; 8 inches at Genesee… Golden gate canyon…Littleton and near Morrison; 7 inches near Nederland; and 6 inches in Louisville. Snowfall totaled 3.6 inches at the site of the former Stapleton International Airport.

16-17

In 1990…strong downslope winds raked the eastern foothills. Wind gusts from 60 to 75 mph were common. Strong winds in metro Denver resulted in wave damage to a dock used to moor several private sail boats at Cheery Creek Reservoir. Damage was confined to the dock and two anchor cables. A northwest wind gust to 43 mph was recorded at Stapleton International Airport.

17

In 1878…strong winds reached sustained speeds of 48 mph.

In 1988…a wind gust to 62 mph was recorded in central Boulder. The strong winds caused a few brief power outages. An old smoldering brush fire in the foothills west of Boulder was re-ignited by the wind gusts.

In 1994…winds gusted to 85 mph atop Squaw Mountain…5 miles south of Idaho Springs.

In 2006…a potent storm system brought heavy snowfall to the mountains and eastern foothills. Snowfall totals in the foothills included: 14 inches at Blackhawk…13.5 inches near Idaho Springs…13 inches at Cabin Creek…12.5 inches at aspen springs and Echo Lake…11.5 inches at Georgetown and Rollinsville…10.5 inches near Jamestown…and 10 inches at Grant and Lake Eldora. Lesser snow amounts…from 4 to 9 inches…were recorded elsewhere in the foothills. Snowfall totaled only 3.5 inches in the Denver Stapleton area. At Denver International Airport…north winds gusted to 31 mph.

In 2012…a brief but powerful windstorm associated with a fast moving cold front across the urban corridor and adjacent plains during in the evening. Peak wind gusts ranging from 58 to 71 mph downed trees and power lines which damaged homes and vehicles. Several temporary structures were also damaged. Approximately fifty thousand were left without power in the Denver…Fort Collins and Greeley areas. Some schools were closed the following day until power could be restored. Around the Denver area…peak wind gusts included: 69 mph in Golden…64 mph at Littleton…  62 mph at Buckley AFB and in Denver…near the intersection of Walnut St. and interstate 25…and Longmont; 59 mph at Centennial Airport…58 mph at Denver City Park… Highlands Ranch.  At Denver International Airport…a peak wind gust to 35 mph was observed from the northwest.

17-19

In 1908…a moist…heavy…wet snowfall totaled 13.0 inches in downtown Denver over the 3 days. Rain from early morning on the 17th changed to snow by late afternoon and continued through the late morning of the 19th. Due to temperatures in the 30’s and melting…the most snow on the ground was only 5.0 inches at 6:00 pm on the 18th. Northwest to northeast winds were sustained between 12 and 20 mph during the storm. Precipitation totaled 1.82 inches.

Weather History

October 4 to October 10: This week in Denver weather history

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This Week in Denver Weather History

A very eventful week in Denver weather history with a wide variety of events from snow to summer-like severe weather. Most notable is five years ago today when multiple tornadoes touched down in the Brighton area.  Read more about all the events below and scroll to a bottom for videos of the 2004 tornadoes.

From the National Weather Service:

From the 3rd to the 4th:

In 1969…the first snowfall of the season totaled 16.0 inches at Stapleton International Airport. There was a thunder snow shower on the evening of the 3rd…but otherwise little wind with the storm. The greatest snow depth on the ground was 8 inches due to melting. Heavy wet snow accumulated on trees…which were still in full leaf…and caused widespread damage from broken limbs and downed utility lines.

From the 3rd to the 5th:

In 1984…the remnants of pacific hurricane polo produced heavy rain over northeastern Colorado. Most locations received between 1.00 to 2.50 inches of rain…but 3.45 inches fell in Littleton. Rainfall totaled 1.73 inches at Stapleton International Airport…where north winds gusted to 24 mph.

On the 4th:

In 1912…sustained south winds to 55 mph with gusts to 60 mph raised the temperature to a high of 83 degrees… The warmest temperature of the month that year.

In 1924…west winds were sustained to 46 mph with gusts to 50 mph in the city. The apparent Bora winds cooled the temperature to a high of 57 degrees from a high of 70 degrees on the 3rd.

In 2004…several small tornadoes touched down near Brighton… Barr lake…and Hudson in Adams and southern weld counties. Most of these caused no damage. However…a small tornado 5 miles southeast of Brighton caused extensive damage to a recreational vehicle and severely damaged a barn. The barn was torn from its foundation…and the roof was thrown 100 feet. Four llamas in the barn were injured when it collapsed.

From the 4th to the 5th:

In 1997…unusually warm weather resulted in two temperature records. High temperature of 87 degrees on the 4th exceeded the old record set in 1922 by one degree. High temperature of 86 degrees on the 5th equaled the record set in 1990 and previous years.

On the 5th:

In 1962…unusually severe thunderstorms for this late in the season affected areas from Boulder northward. Hail up to golf ball size and strong gusty winds did much damage to roofs…windows…and signs in Boulder. Heavy rainfall caused local flooding.

In 1994…lightning caused a power outage to over 2400 homes for a few hours in and around Nederland in the foothills southwest of Boulder. Very strong winds accompanied the thunderstorm. Thunderstorm winds gusted to 60 mph and hail to 1/2 inch diameter fell in Lafayette. Strong microburst winds gusting to 69 mph near Strasburg caused an oil rig to topple onto two vehicles…injuring one person. The strong winds in the area also downed a few power poles… But caused power outages to only a few homes.

In 1995…strong winds spread from the foothills onto the plains. Wind gusts to 77 mph were reported atop squaw mountain west of Denver. On the plains…winds gusted to 60 mph at Kennesburg and to 62 mph near Strasburg. North winds gusted to 41 mph at Denver International Airport.

On the 6th:

In 1900…northwest winds were sustained to 40 mph with gusts as high as 50 mph in downtown Denver.

In 1903…northwest winds were sustained to 40 mph with gusts to 50 mph. The strong winds warmed the temperature to a high of 71 degrees in the city. The low reading was only 46 degrees.

In 1910…light smoke from forest fires drifted over the city.

In 1976…an arctic cold front brought light snow over the foothills above 6 thousand feet. Traffic was snarled at many locations. Only a trace of snow fell at Stapleton International Airport where rainfall totaled 0.20 inch and northeast winds gusted to 41 mph.

In 1991…the brilliant orange sunset was apparently the result of an extensive volcanic smoke layer in the upper atmosphere.

In 1994…strong west to northwest winds developed in the foothills above 9500 feet. A wind gust to 78 mph was recorded atop squaw mountain west of Denver and to 72 mph at ward northwest of Boulder. Northwest winds gusted to 35 mph at Stapleton International Airport.

In 2011…strong winds developed in and around the Denver area ahead of an approaching storm system. At the National Wind Technology Center…peak wind gusts ranged from 79 to 92 mph during the early morning hours. Across metro Denver…the strong winds toppled a few trees and damaged patio furniture. The wind caused a few flight delays at Denver International Airport due to a partial ground stoppage of incoming flights. Peak wind reports also included: 66 mph at Cedar Point…63 mph at Denver International Airport…60 mph at Buckley Air Force Base; 59 mph at Highlands Ranch; 58 mph at Deer Trail and Rocky Mountain Metro Airport in Broomfield; 55 mph at Bennett…Centennial Airport and City Park in Denver.

On the 7th:

In 1903…north winds were sustained to 40 mph with gusts to 48 mph.

In 1917…post-frontal northwest winds were sustained to 45 mph with gusts to 52 mph. Rain was mixed with a trace of snow…the first of the season. Precipitation totaled 0.22 inch and included the occurrence of hail even though no thunder was heard.

In 1950…strong winds caused a power outage in Boulder. This was the heaviest windstorm since January. Damage was minor. Northwest winds gusted to only 35 mph at Stapleton Airport.

In 1985…strong Chinook winds buffeted the Front Range foothills. Wind gusts between 60 and 70 mph were reported in Boulder and atop squaw mountain west of Denver. Southwest winds gusted to 41 mph at Stapleton International Airport.

From the 7th to the 8th:

In 1990…the season’s first snow occurred. Snowfall amounts varied from 3 to 7 inches across metro Denver. Snowfall totaled 4.0 inches at Stapleton International Airport where north winds gusted to 29 mph.

Continue reading October 4 to October 10: This week in Denver weather history →

Climatology, Thornton Weather

Thornton’s October 2026 preview: Generally calm conditions with our first freeze and snow

The month of October.

With the first full month of fall here, October usually brings one of the quietest weather months in the Denver area with plenty of mild, sunny days and clear, cool nights.

October is historically the second sunniest month and conditions are generally calm.

However we also will usually see our first taste of winter during the month with the first freeze and first snowfall of the season.  Temperatures as well will start to drop and by the end of the month the average nighttime lows are below freezing.

For complete details on our historical October weather and what we can expect in the coming month, read our complete October weather preview here.

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Weather History

September 27 to October 3: This week in Denver weather history

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This Week in Denver Weather History

With the end of summer and the arrival of fall, looking back at Denver weather history we start to see more mentions of snow.  It is of course not the only notable weather event this time of year.  We still have received severe thunderstorms, damaging winds, and 90 degree plus heat.

From the National Weather Service:

From the 25th to the 27th:

in 1996…an early season snowstorm brought heavy snow to the Front Range eastern foothills.  Snowfall totals included:  8 to 12 inches around Conifer…7 inches on Floyd Hill…and 6 inches at both bailey and Chief Hosa. Snowfall totaled only 4.7 inches at the site of the former Stapleton International Airport.  This was the first measurable snow of the season.  After the passage of a strong cold front…north winds gusted to 38 mph at Denver International Airport on the 25th.

From the 26th to the 28th:

In 1936…the heaviest snowfall ever recorded in September and the heaviest snowfall ever recorded so early in the season dumped a total of 16.5 inches of snow on downtown Denver and 21.3 inches at Denver municipal airport.  The 15.0 inches of snow measured from 6:00 pm on the 27th to 6:00 pm on the 28th is the greatest 24 hour snowfall ever recorded in September.  This was the first snow of the season.  The snow was intermittent through the 26th…but continuous from early afternoon on the 27th to around midnight on the 28th…except for a period of rain during the afternoon of the 28th which contributed to a loss of depth on the ground.  The greatest snow depth on the ground downtown was 13 inches with 8 inches at Denver municipal airport.  There were no high winds with the storm and traffic was interrupted for only a short period.  The storm produced property damage estimated at 7 million dollars.  With trees and shrubs in full foliage…the leaves caught and held the heavy water-laden snow…until the branches snapped from the weight.  More than 3000 workmen were called to remove the debris and snow from the city.  The city firemen who were off duty…as well as all the reserves… Were asked to report to their stations.  All schools in the city remained open…but attendance was only 50 percent of normal.  Grade school students were sent home at noon on the 28th.  The early storm caught stockmen with many cattle still in higher ranges.  Warm weather followed the snow…which had all melted by the end of the month…except for a few inches in sheltered places.

On the 27th:

In 1877…smoke from heavy forest fires in the mountains spread over the city on upper wind currents.

In 1935…the first snow of the season was 2.8 inches in downtown Denver.  The low temperature dipped to 31 degrees for the first freeze of the season.

From the 27th to the 28th:

In 1984…heavy snow fell over the plains and foothills. Snowfall amounts ranged from 2 to 5 inches on the plains with up to a foot at higher elevations in the foothills. The main problem caused by the storm was thousands of power outages caused by snow-laden tree limbs snapping and falling onto power lines.  Over 15 thousand homes lost power in metro Denver.  Some cars were damaged by falling trees and limbs.  The snow also caused some flight delays at Stapleton International Airport where 5.1 inches of snow fell and northeast winds gusted to 29 mph.  Maximum snow depth on the ground was 3 inches due to melting.  The high temperature of only 34 degrees on the 28th was a record low maximum for the date and equaled the all-time record for the month at that time.

On the 28th:

In 1877…heavy dense smoke from mountain forest fires spread over the city.  The smoke was so dense that it obscured the sun at times.

In 1921…post-frontal northeast winds were sustained to 44 mph.

In 1953…a pacific cold front produced a west wind gust to 59 mph at Stapleton Airport where the visibility was briefly reduced to 3/4 miles in blowing dust.  Strong winds were also widespread over Boulder during the afternoon.

In 1960…strong…gusty winds tore the roof from 6 units of a motel on west Colfax Avenue in Denver.  The roofing sailed over the building and crashed down on a truck…wrecking it. The strong winds were the result of an apparent microburst.

In 1999…snow fell in the foothills west of metro Denver and over the plains.  Snowfall totals included 7 inches at Conifer.  At the site of the former Stapleton International Airport…3.1 inches of snow were measured.  This was the first snow of the season.  The heavy wet snow snapped branches from fully leafed trees…downing power lines and causing scattered outages.

In 2004…severe thunderstorms produced hail to 3/4 inch in diameter in Littleton and in Douglas County 14 miles northwest of Castle Rock.

In 2012…a weak tornado (ef-0) tornado touched down near Strasburg. No damage was reported.

From the 28th to the 29th:

In 1959…one of the heaviest September snow storms of record began as rain and changed to heavy wet snow.  The storm caused heavy damage to trees and shrubbery…which were still in full leaf.  The storm dumped 10.6 inches of snow at Stapleton Airport…the third heaviest September snow amount to date.  Falling trees and limbs disrupted traffic…broke power and communication lines…and damaged buildings and cars.  One man was killed in Denver by a falling tree limb…and four others died of heart attacks while shoveling snow or trying to move heavy tree limbs.  Direct costs of the storm for cleaning up debris…repairing utility lines…and damage to buildings and other property across all of eastern Colorado were estimated to be over a half million dollars.  The value of trees destroyed or damaged was estimated to exceed five million dollars.  North-northeast winds gusted to 32 mph at Stapleton Airport on the 28th.

In 1985…an unusually cold air mass for this time of year settled over the area.  Metro Denver received 8 to 12 inches of powdery snow.  The 8.7 inches of snow that fell at Stapleton International Airport was the first measurable snow of the season and the city’s heaviest September snowfall since 1971.  The snow caused flight delays of over 2 hours at Stapleton International Airport. I-70 was closed for a time west of Denver.  Snow-laden tree limbs snapped over all of metro Denver…causing widespread power outages.  Ten thousand people were without electricity for a time in Boulder.  The morning of the 29th saw mid-winter temperatures along the Front Range.  The temperature dipped to 17 degrees…the lowest temperature ever recorded in September in Denver.  The high temperature of only 29 degrees on the 29th was a new record low maximum for the date and lowest ever recorded during the month of September.  The low temperature of 21 degrees on the evening of the 28th set a new record low for the date.  The cold weather persisted through the 1st with record minimum temperatures of 25 degrees set on the 30th and 27 degrees set on October 1st.

On the 29th:

In 1966…a vigorous cold front moved thru metro Denver. North winds gusting to 51 mph kicked up billows of blowing dust…which briefly reduced the visibility to 1 mile at Stapleton International Airport.  The cold air caused temperatures to drop rapidly from a high of 86 degrees to a low of 46 degrees by days end.

In 1985…the lowest temperature ever recorded in September… 17 degrees…occurred.  The high temperature warmed to only 29 degrees…the all-time record low maximum for the month.

In 1994…the temperature reached a high of 91 degrees at Stapleton International Airport.  This was the 60th day of the year that the temperature had reached 90 degrees or more…establishing a new record at that time.  The previous record of 52 “90 degree days” occurred in 1978. Only 43 “90 degree days” were recorded at Denver International Airport during 1994.

In 1995…lightning struck a couple in Aurora as they were walking in the rain.  The bolt struck the umbrella the man was carrying…injuring both the man and his wife.

In 2000…late afternoon thunderstorms produced strong wind gusts to 76 mph in Westminster…to 69 mph near Boulder…and to 60 mph at Jefferson County airport near Broomfield.  No damage was reported.

In 2014…a storm system that moved through the area produced large hail and street flooding in parts of metro Denver and then spread east into the plains. The storm also caused multiple accidents. A semi became detached from a trailer… Blocking traffic on westbound Interstate 70 west of Tower Road. Downed power poles blocked a roadway on CO 79 near Bennett…at mile marker 10. In addition to the damaging winds…the storms produced large hail… From nickel to golfball size across southern and eastern portions of metro Denver. The hailstorm was the most damaging of the 2014 summer season…with insured losses that topped 213 million dollars. Insurance claims included 29297 automobile claims worth more than 87.2 million dollars and 14287 property claims for 126 million dollars…ranking the storm as the eighth most expensive to hit the state. At Denver International Airport…1.01 inches of rainfall was recorded which was the greatest 24-hr rainfall for the date. In addition…a peak wind gust to 38 mph was observed at the airport.

In 2015…severe thunderstorms developed over the foothills of Boulder County and Jefferson Counties…then moved south along the western suburbs of Denver. Areas north of Golden… around Lakewood and into northern Douglas County saw the heaviest rain and hail. The hail ranged in size from nickel to ping pong size.

On the 30th: Continue reading September 27 to October 3: This week in Denver weather history →

Weather History

September 20 to September 26: This week in Denver weather history

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This Week in Denver Weather History

Looking back at this week in Denver history we start to see more of the signs that summer is coming to an end and fall and winter are right around the corner.  Summer-like severe weather can still occur but we also start to see more cold temperatures and occasions with snow become more prevalent.

From the National Weather Service:

20

In 1921…an apparent Bora produced northwest winds sustained to 44 mph with gusts to 64 mph.

In 1955…hail stones 1/2 to 3/4 inch in diameter were reported across parts of the city of Denver.

In 1992…weather observers at Buckley Air National Guard base sighted two tornados southeast of the base.  The tornados were short-lived and caused no injuries or damage.

20-21

In 1963…heavy rain and hail caused local flooding in southeast Denver.  Thunderstorm rainfall was only 0.60 inch at Stapleton Airport on the 20th.

In 1983…the cold front on the 19th brought an unusually cold air mass into metro Denver for so early in the season.  The temperature dipped to a daily record minimum of 28 degrees on both days.

In 1995…a vigorous late summer storm brought the season’s first heavy snow to portions of metro Denver.  Millions of trees were damaged and power lines downed as 4 to 8 inches of heavy wet snow settled on fully leafed trees in the Boulder and Denver areas.  Branches snapped and trees split under the weight of heavy snow…downing power lines. Firefighters responded to numerous transformer fires. Around 100 thousand people were left without electricity in Boulder and Denver areas alone.  It took over a week to fully restore power to some areas.  Insurance claims were estimated to be around 6 million dollars to homes in metro Denver and about 500 thousand dollars in damage to automobiles.  It was estimated that about 80 percent of 125 million dollars worth of city owned trees in Denver were damaged.  Snowfall totaled 7.4 inches at the site of the former Stapleton International Airport where the greatest depth of snow on the ground was only 4 inches due to melting.  Temperature records were set on the 21st when the thermometer dipped to a record low reading of 27 degrees and climbed to a high of only 36 degrees… Setting a record low maximum for the date.  North winds gusted to 29 mph at Denver International Airport on the 20th.

20-22

In 1902…a thunderstorm on the 20th…in advance of an apparent cold front…produced rain…hail…and northwest winds to 40 mph with gusts to 48 mph.  Widespread rain developed behind the cold front and totaled 3.21 inches from the evening of the 20th through the early afternoon of the 22nd.  The 2.70 inches of precipitation recorded from 800 pm on the 20th to 800 pm on the 21st is the greatest 24 hour precipitation ever recorded in the month of September.  The temperature dipped from a high of 80 degrees on the 20th to a high of only 51 degrees on the 21st.

21

In 1951…4.2 inches of snow fell at Stapleton Airport… Where northeast winds gusted to 27 mph.  This was the first snowfall of the season in Denver…marking the end of the second shortest snow-free period on record…109 days…from June 4th through September 20th.  A trace of snow fell on June 3rd.

In 1984…thunderstorm winds gusted to 56 mph at Stapleton Airport.

In 1992…the only precipitation of the month at Stapleton International Airport…0.01 inch of rain…fell from a brief shower around daybreak.
21-22 in 1870…strong winds occurred in the foothills and in Boulder and Denver.

In 1895…rain changed to snow overnight and totaled 11.4 inches in downtown Denver.  This was the first snowfall of the season and the second heaviest first snowfall of the season on record.  North winds were sustained to 27 mph with gusts to 30 mph on the 21st.

In 2009…an early season storm brought moderate to heavy snow to the foothills of clear creek…Jefferson and Park counties…west and southwest of Denver. A trained spotter…4 miles west-northwest of Conifer… Was the big winner with 14 inches of snow. Storm totals elsewhere generally ranged from 5 to 10 inches.

22

In 1913…a thunderstorm produced northwest winds sustained to 40 mph with gusts to 44 mph.

In 1946…a trace of snow fell in downtown Denver.  This marked the start of the longest snow season on record… 263 days through June 11…1947…when a trace of snow also fell.

Continue reading September 20 to September 26: This week in Denver weather history →

Weather History

September 13 to September 19: This week in Denver weather history

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This Week in Denver Weather History

Weather conditions in Colorado can of course vary greatly and we always see that in our weekly look back in the history books.  For this week, we see a dizzying array of weather events from record setting temperatures in the 90’s and summer-like thunderstorms with tornadoes to an early arrival of winter that brought a foot of snow!

From the National Weather Service:

1-30

In 2020…a worsening drought that started in the spring and continued through September. Outside of an early season snow on the 8th…the month of September was another unseasonably warm and dry period. The combination of hot…mostly dry conditions…and critically dry fuels… resulted in a continuation and rapid expansion of several massive wildfires. The Cameron Peak fire…which became the largest in the state`s history started on August 13th…and continued through September. As a result…very poor air quality continued to impact Denver and the entire Front Range. Denver recorded the most days ever with a high temperature of 90 degrees or better; 75 days. The last of which was 91 degrees on the 24th. The previous record was 73 days set in 2012.

5-13

In 2010…the Fourmile Canyon wildfire…northwest of Boulder… Broke out on the morning of the 5th. It originated from an unattended fire pit at a local residence. The wildfire quickly consumed 5 1/2 square miles or 3500 acres the first day…and forced the evacuation of over three thousand residents. Erratic 45-mph gusts sent the fire in two directions at times. Very dry weather conditions preceded the fire. The combination of strong winds…low relative humidities and dry fuels allowed the wildfire spread rapidly through the steep…heavily forested terrain. The flames were reportedly 20 to 50 feet in length. Towns within the burn area included Salina…Wallstreet and Gold Hill. The dry conditions coupled with gusty winds ranging from 45 to 64 mph persisted for several more days. Fire managers used as many as 700 firefighters and support personnel from 35 agencies and seven air tankers to battle the wildfire. A total of 6181 square acres or approximately 10 square miles were burned. The Fourmile Canyon wildfire was the most destructive fire in Colorado history in terms of the damage to personal property. It destroyed 171 homes with an estimated cost of 217 million dollars.

10-18

In 2018…the high temperature equaled or exceeded 90 degrees for 9 consecutive days; marking the first time such an occurrence has taken place in the month of September. It also brought September of 2018 into a 4-way tie for most 90 degree + days in the month. Previous years included 2017…2005 and 1895. During the streak…4 record high temperatures were either tied or broken…and one record high minimum temperatures was broken.

11-16

In 2013…a deep southerly flow over Colorado… Ahead of a nearly stationary low pressure system over the great basin… Pumped copious amounts of monsoonal moisture into the area. In addition…a weak stationary front stretched along the Front Range foothills and Palmer Divide.  This resulted in a prolonged period of moderate to heavy rain across the Front Range foothills…Palmer Divide…urban corridor. By the 14th…storm totals ranged from 6 to 18 inches… Highest in the foothills of Boulder County. The headwaters then moved down the South Platte River and caused widespread flooding with record flood stages at several locations as it made its way downstream.  The record high flood stages resulted in widespread flooding along the South Platte River basin. The flood damage encompassed 4500 square miles of the Front Range…left 7 dead… Forced thousands to evacuate…and destroyed thousands of homes and farms. Record amounts of rainfall generated flash floods that tore up roads and lines of communication… Leaving many stranded. Nearly 19000 homes were damaged… And over 1500 destroyed. Colorado department of transportation estimated at least 30 state highway bridges were destroyed and an additional 20 seriously damaged. Preliminary assessments of the state`s infrastructure showed damage of $40 million to roads and $112 million to bridges. Repair costs for state and county roads ran into the hundreds of millions of dollars. Miles of freight and passenger rail lines were washed out or submerged… Including a section servicing Amtrak`s iconic California Zephyr. The town of Lyons was isolated by the flooding of St. Vrain creek…and several earth dams along the Front Range burst or were over-topped. Floodwaters swept through Estes Park; damaged hundreds of buildings and destroyed large sections of U.S. 34 from Loveland and U.S. 36 from Lyons to Boulder. U.S. 34 suffered the most damage… With 85 percent of its roadway and bridges destroyed. In Weld County…about nearly two thousand gas wells were damaged and had to be closed off as the floodwaters inundated entire communities. Sewage treatment plants and other utilities were knocked out in a number of towns. Governor Hickenlooper declared a disaster emergency on September 13th…in 11 counties across northeast Colorado including:  Adams…Arapahoe…Broomfield…Boulder…Denver…  Jefferson…Larimer…Logan…Morgan… Washington and Weld. By the 15th…federal emergency declarations covered those counties as well as Clear Creek County. Projected losses from the flooding statewide was nearly two billion dollars in property damage…according to Eqecat… A catastrophe modeling firm.  The damage was most severe in and around Lyons and Boulder.  More than 11 thousand people were evacuated…reportedly the largest since Hurricane Katrina. President Obama declared a state of emergency for Boulder and Larimer counties.  An additional 10 counties were added on the 16th and included: Adams… Arapahoe…Broomfield…Clear Creek…Denver…Jefferson…  Morgan…Logan… Washington and Weld counties. The president also declared a major disaster specifically for Boulder County.  There were six fatalities directly attributed to flash flooding. Two 19-yr old teenagers died on the 11th…after they were swept away by floodwaters after abandoning their car on Lindon Drive in Boulder. In Jamestown…a 72-yr old man was killed when the building he was in collapsed. An 80-yr old Lyons resident died in the early morning hours of the 12th…when his truck was swept into the St. Vrain River near his home. Later on the 12th…a 79-yr old Larimer County resident was killed when she was swept away while trying to climb to safety from her home in Cedar Point. A 61-yr old cedar point resident died when her home was swept down the Big Thompson River by the floodwaters. An 80-yr old Idaho Springs resident drowned in Clear Creek when the embankment he was standing on collapsed. In Boulder…some of the monthly records broken included: one-day all-time record: 9.08 inches which shattered the previous wettest day of 4.8 inches set on July 31… 1919; one-month record of 18.16 inches…which broke the previous all-time monthly record of 9.59 inches set in May of 1995; wettest September on record which broke the previous record of 5.5 inches set in September of 1940; one-year record of 34.15 inches broke the previous wettest year of 29.93 inches set in 1995. At Denver International Airport…the total precipitation for the month of September was 5.61 inches…which was 4.65 inches above the normal of 0.96 inches. This is the most precipitation ever recorded in Denver for the month of September. Daily precipitation records included 1.11 inches on the 12th and 2.01 inches on the 14th.

13

In 1899…west winds were sustained to 43 mph with gusts to 46 mph.

In 1928…northwest winds were sustained to 41 mph with gusts to 45 mph.

In 1937…an apparent dry microburst produced brief north winds sustained to 31 mph with gusts to 41 mph.  There was a trace of rain.

In 1982…torrential rains drenched both the foothills and plains from Denver north.  While the heaviest rain occurred north of Denver…just east of Denver 2 1/3 inches of rain fell in 5 hours along with hail that caused minor damage to a few airplanes.  Thunderstorm rainfall totaled 0.83 inch at Stapleton International Airport.

In 1993…an upper level system combined with a cold and moist upslope flow to bring the heaviest snowfall to metro Denver for so early in the season.  Snowfall from the storm totaled 5.4 inches at Stapleton International Airport; however…most of the snow melted as it fell leaving a maximum of one inch on the ground at any one time.  North winds gusted to 21 mph at Stapleton International Airport where a record low temperature of 33 degrees for the date was observed.

In 2002…Friday the 13th proved to be bad luck for several motorists when heavy thunderstorm rainfall caused flooding on I-25 in central Denver.  Water rose several feet under the Logan Street overpass…inundating several vehicles. Some motorists were rescued…while others simply waited atop their cars for the flood water to recede.  The highway had to be closed in both directions for about 3 hours.  The flooding was exacerbated by poor drainage due to the construction along the highway.  A 12-foot drainage pipe had not yet been installed beneath the underpass.  The deluge also flooded several businesses along Broadway.

In 2009…a severe thunderstorm produced large hail… Up to half dollar size in the foothills of Jefferson County…west of Denver.

14

In 1912…snow fell for most of the day…but melted as it fell. Precipitation from melted snow was 0.46 inch.  Some sleet was also observed.  Total precipitation was 0.61 inch.  North winds were sustained to 15 mph with gusts to 17 mph.

In 1934…a moderate dust storm blew into the city at 4:15 pm. North winds were sustained to 35 mph with gusts to 44 mph. By 5:25 pm the winds had decreased and the storm had ended. A trace of rain fell during the evening.

In 1976…a tornado touched down just west of I-25 between Arapahoe Road and Dry Creek Road…tearing the roof from a house.  Nearby…a high tension wire fell on a house causing damage…and lightning ripped a hole in the side of a house. Three tornadoes were observed just east of Stapleton International Airport and northeast of Buckley Field.  No damage was reported.  Dime to quarter size hail fell in northeast Denver with only 1/4 inch hail at Stapleton International Airport.  The Colorado State Patrol reported golf ball size hail 4 miles west of Franktown.  A funnel cloud was sighted 4 miles north of Franktown.

In 1983…a thunderstorm produced winds gusts as high as 56 mph across metro Denver along with thick blowing dust. Power was knocked out in many locations.  Thunderstorm winds gusting to 49 mph briefly reduced the visibility to 2 miles in blowing dust at Stapleton International Airport.

In 1996…a 54-year-old woman was struck by lightning near Franktown…as she was preparing an outdoor barbeque.  The woman was knocked unconscious…but received only minor injuries.  Thunderstorms over southern Jefferson County dumped heavy rain in the buffalo creek area.  Some minor roads were washed out by flash flooding…but no other damage was reported.  Hail ranging in size from 1/2 to 3/4 inch in diameter fell at the site of the former Stapleton International Airport.

In 2006…a microburst from a thunderstorm produced sustained winds to 40 mph with gusts to 53 mph at Denver International Airport.

Continue reading September 13 to September 19: This week in Denver weather history →

Weather History

September 6 to September 12: This week in Denver weather history

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This Week in Denver Weather History

Colorado weather is certainly varied and this week’s look back at weather history proves that.  We have seen everything from deadly lightning, hail and severe winds to even snow during the second week of September.  Most notably however were the devastating – and deadly – floods of 2013.

1-7

In 1978…the temperature reached 90 degrees or more on seven consecutive days with the highest temperature…94 degrees… Recorded on both the 4th and 6th.

1-30

In 2020…a worsening drought that started in the spring and continued through September. Outside of an early season snow on the 8th…the month of September was another unseasonably warm and dry period. The combination of hot…mostly dry conditions…and critically dry fuels… resulted in a continuation and rapid expansion of several massive wildfires. The Cameron Peak fire…which became the largest in the state`s history started on August 13th…and continued through September. As a result…very poor air quality continued to impact Denver and the entire Front Range. Denver recorded the most days ever with a high temperature of 90 degrees or better; 75 days. The last of which was 91 degrees on the 24th. The previous record was 73 days set in 2012.

3-6

In 1909…rainfall for the 4 days accumulated to 3.97 inches in Boulder…while in Denver rainfall totaled 2.45 inches on the 4th…5th…and 6th.

5-8

In 2020…a strong upper level low brought an end to record heat to the Front Range urban corridor…and provided Denver its second earliest measurable snowfall on record. Numerous heat records were set leading up to the snowfall…and several new snowfall and cold records were also broken in this abrupt bout with winter. Denver set its all time record high for September…reaching 101 degrees during the afternoon. This was also the latest date a 100 degree reading has ever been observed in Denver. Another daily record high was then tied on September 6th when Denver hit 97 degrees. September 7th was the last day of heat when Denver`s high temperature reached 93 degrees. That tied Denver for the record for the number of 90 degree days for a year at 73…and was also the warmest temperature ever recorded before a day of measurable snowfall. By the evening of September 7th…a series of cold fronts progressed southward from Wyoming into Colorado… dropping the temperature into the low 30s by the early morning hours of September 8th. Snow developed across the Front Range mountains and foothills overnight… while a mix of rain and snow developed along the I-25 corridor. A few locations picked up light snowfall accumulations in the morning. Accumulating snow was mostly confined to the higher elevations much of the day…before spreading across the plains during the late afternoon and evening. Storm totals ranged from 4 to 10 inches in the mountains…with 3 to 6 inches near the foothills. A total of 5.6 inches of snow was measured at the NWS Boulder office…while at Denver International Airport…the official measurement was 1.0 inch.

5-9

In 1988…layers of smoke aloft from large forest fires in Yellowstone National Park completely obliterated the sun at times.  At Stapleton International Airport…surface visibility was reduced at times to 5 and 6 miles in smoke.

5-13

In 2010…the Fourmile Canyon wildfire…northwest of Boulder… Broke out on the morning of the 5th. It originated from an unattended fire pit at a local residence. The wildfire quickly consumed 5 1/2 square miles or 3500 acres the first day…and forced the evacuation of over three thousand residents. Erratic 45-mph gusts sent the fire in two directions at times. Very dry weather conditions preceded the fire. The combination of strong winds…low relative humidities and dry fuels allowed the wildfire spread rapidly through the steep…heavily forested terrain. The flames were reportedly 20 to 50 feet in length. Towns within the burn area included Salina…Wallstreet and Gold Hill. The dry conditions coupled with gusty winds ranging from 45 to 64 mph persisted for several more days. Fire managers used as many as 700 firefighters and support personnel from 35 agencies and seven air tankers to battle the wildfire. A total of 6181 square acres or approximately 10 square miles were burned. The Fourmile Canyon wildfire was the most destructive fire in Colorado history in terms of the damage to personal property. It destroyed 171 homes with an estimated cost of 217 million dollars.

6

In 1940…a thunderstorm pelted the city with small hail. The storm produced some lightning damage.  One woman was stunned by a bolt which struck near her.  Heavy rain from the storm raised the level of Cherry Creek by more than 3 feet during the height of the storm.  Rainfall downtown was only 0.26 inch.

In 1988…strong winds blew down two houses that were under construction in Castle Rock.  Northwest winds gusted to 44 mph at Stapleton International Airport.

In 1993…a man was struck and killed by lightning while standing outside his home in unincorporated Arapahoe County 11 miles south of Denver.  Lightning also struck a cabin in Marshdale…20 miles southwest of Denver…which started a fire and damaged one room and a portion of the roof.

In 1995…hail as large as 3/4 inch in diameter fell in Coal Creek Canyon in northern Jefferson County.

In 2001…a thunderstorm dropped 3/4 inch diameter hail in Aurora near Cherry Creek.

7

In 1875…the creeks were running dangerously high during the night from heavy rains in the mountains.

In 1885…a thunderstorm produced very white hail of irregular shape and about the size of beans.  Precipitation was only 0.10 inch.

In 1971…a vigorous cold front accompanied by a thunderstorm produced wind gusts to 48 mph at Stapleton International Airport and much upslope cloudiness and light rain across metro Denver.

In 1989…widespread thunderstorms produced lightning strikes that knocked out power to about 13 thousand homes in Boulder County.  In a rugged area stripped of vegetation by a forest fire earlier in July…heavy rain triggered mud slides that destroyed one home and severely damaged another in Boulder canyon 10 miles west of Boulder.  In one home…the mud caved in an exterior wall and poured into the residence only seconds after 2 people had evacuated the premises. Rainfall totaled 1 to 3 inches.  Hail 1 3/4 inches in diameter fell in Nederland…Idaho Springs…and Golden Gate Canyon.  Hail 1 inch in diameter was measured 10 miles north of Golden.

In 1993…thunderstorm winds toppled an overhead sign onto the intersection of I-70 and I-25 in Denver…causing considerable damage to 4 vehicles.  The winds also caused a police car to be blown off the road northeast of Denver. Thunderstorm winds gusting to 66 mph damaged the siding of a residence southeast of Brighton.  A thunderstorm wind gust to 53 mph was recorded at Stapleton International Airport.  Hail to 7/8 inch in diameter fell at Kittredge in the foothills of Jefferson County.

In 1994…lightning severely damaged a public television transmitter atop squaw mountain west of Denver.

7-8

In 1884…a windstorm from mid-afternoon until the early morning hours of the 8th produced south winds sustained to 48 mph.  The strong winds toppled several trees in the city.

In 1892…there was a trace of rainfall each day.  This together with a trace of rain on both the 2nd and 3rd was the only rainfall of the month…making the month the driest on record.  The record was equaled in 1944.

8

In 1886…the last thunderstorm of the season pelted the city with hail the size of beans and dropped 0.81 inch of precipitation.

In 1962…the earliest first freeze of the season occurred. The temperature dipped to a low of 31 degrees.

In 1973…hail up to 1 1/2 inches in diameter fell northeast of Boulder.  A tornado was reported by a pilot east of Parker.  No damage was reported.

9

In 1933…heavy rain in the foothills over the clear creek and Golden gate canyon watersheds caused flooding in Golden and damaged the roadway in Golden gate canyon… Which resulted in its closure.

In 1969…a funnel cloud was sighted in southeast Denver. There was also considerable thunderstorm activity and local heavy rain across metro Denver.  Rainfall totaled 1.30 inches at Stapleton International Airport where small hail also fell.

In 1973…hail from 3/4 inch to 1 3/4 inches in diameter fell in Westminster and south of Broomfield.

In 2009…a man was critically injured when he was struck by lightning while riding his bicycle.  He was nearing a paramedic van when he was hit.  His heart stopped but paramedics quickly responded and were able to resuscitate him.

In 2011…a man was struck by lightning at the Adams County Fairgrounds.  He was leaning against a tree while watching a cross country meet when the tree was hit.  The lightning traveled down the tree and up through the ground…using him as a conductor.  The victim received second and third degree burns.

Continue reading September 6 to September 12: This week in Denver weather history →

Climatology, Thornton Weather

Thornton’s September 2026 preview: Usually one of the most pleasant months of the year

Thornton's September weather preview.
Thornton’s September weather preview.

Following a summer that was unseasonably warm and dry, we find ourselves heading into September hoping for relief.  The month can bring plenty of rain and even our first snow of the season but more often than not, it is one of the most pleasant along the Colorado Front Range.

As temperatures start to drop, September usually reminds us that summer is at an end and fall is now here. Sunshine is predominant though as the month actually has the highest percentage of sun out of any month. Sunny days and clear, cool nights are the standard weather pattern for the month.

The month can bring extremes however.  We will of course forever remember 2013’s devastating floods brought on by record-setting rain.  Longtime residents might remember September 1971 which brought over 17 inches of snowfall.

Get a complete look at September’s weather and more details as to what we can expect this year here.

Weather, natural disasters & climate news and information.