Today in Thornton the temperatures climbs to about 10 degrees above average for the date. We will also enjoy lots of blue sky above.
Sunny skies will be the rule throughout the daytime hours. Conditions will be calm and dry. Highs will reach the low to mid-80s, well above the average high for the date of 72 degrees.
Tonight, we remain calm. Lows will dip to around 50 degrees under mostly clear skies.
Thornton was finally able to break out of the hot, dry weather pattern of recent months and see things get a bit more normal. September historically is one of our most pleasant months and 2025 largely held true to that.
We did start out pretty mild and precipitation was meager for the first half of the month. Finally, on the 13th, we began to see things cool down and then on the 16th got a nice shot of rain (0.61”).
The rest of the month offered mild but comfortable temperatures. A strong trough on the 23rd cooled us considerably with that day offering high temperatures nearly 20 degrees below normal. It also brought a very healthy shot of rain (1.21″).
In the end, the average temperature for the month of September ended up very close to average. Thornton’s average for the month was 64.6 degrees. This was just a hair higher than our 19 year running average for the month of 64.3 degrees. Our maximum temperature for the month was 92 degrees and came on the 10th. Our coolest reading of 42.3 degrees was on the 25th.
For Denver, at Denver International Airport where the Mile High City’s official measurements are taken, temperatures were on par with ours. They reported an average for the month of 64.7 degrees. This was close to their long term average for September of 64.8 degrees.
In terms of precipitation, Thornton saw a notable 2.09 inches for the month. This was far above our 19-year running average of 1.51 inches for September. This was the fourth wettest September over that period.
The Mile High City was quite a bit drier with 1.35 inches recorded in their rain bucket. It was, however, above their long term average for the month of 1.09 inches.
No snow was recorded in Thornton or Denver for the month.
Click here to view Thornton’s complete September 2025 climate summary report.
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.
The month of September is typically one of the more pleasant months in Colorado. Temperatures are usually comfortable and there is not normally a lot of weather drama. That however does not mean there aren’t plenty of photo opportunities.
Wildlife is still quite active along the Front Range and flowers will hold on to their petals for at least the first part of the month. Then of course there is the weather which you never know what to expect. Thunderstorms, heavy rain, and even snow are a possibility.
Showcasing images captured by ThorntonWeather.com readers as well as some of our own, our monthly slideshow covers the entire gamut of weather-related imagery.
Sunsets, sunrises, wildlife and of course every type of weather condition are vividly depicted in images captured from yours and our cameras.
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What is missing in the slideshow above? Your photo!
Our monthly photo slideshow is going to feature images that we have taken but more importantly images that you have captured. The photos can be of anything even remotely weather-related.
Landscapes, current conditions, wildlife, pets, kids. Whimsical, newsy, artsy. Taken at the zoo, some other area attraction, a local park, a national park or your backyard. You name it, we want to see and share it!
Images can be taken in Thornton, Denver or anywhere across the extraordinary Centennial State. We’ll even take some from out of state if we can tie it to Colorado somehow.
We’ll keep the criteria very open to interpretation with just about any image eligible to be shown in our slideshows.
What do you win for having your image in our slideshow? We are just a ‘mom and pop’ outfit and make no money from our site so we really don’t have the means to provide prizes. However you will have our undying gratitude and the satisfaction that your images are shared on the most popular website in Thornton.
To share you images with us and get them included in the slideshow just email them to us or share them with ThorntonWeather.com on any of the various social media outlets. Links are provided below.
So come on, get those camera’s rolling!
Late September and early October are usually relatively calm in Denver however that isn’t always the case. In our look back at his week in weather history, we see that heavy, wet snow can arrive causing extensive damage – and even death. Severe thunderstorms have also occurred bringing large hail and even tornadoes.
From the National Weather Service:
26-28
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.
27-28
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.
28
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.
28-29
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.
29
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.
30
In 1898…south winds were sustained to 41 mph with gusts to 54 mph.
In 1940…a late season thunderstorm in the city caused one lightning death.
In 1944…the month ended with a trace of rain on this date and for the month. A trace of rain also occurred on the 4th…9th…and 10th. There was no measurable precipitation for the month. The total of a trace of precipitation for the month equaled the driest September on record first set in 1892.
In 2009…a trained spotter in Coal Creek Canyon…recorded a peak wind gust to 88 mph.
Continue reading September 28 to October 4: This Week in Denver Weather History
This time of year many folks start thinking about heading to the hills west of Denver in search of gold – fall foliage gold.
Where to go? Below are five of ThorntonWeather.com’s favorite ones near Denver – plus a few further out and some bonus ideas. After that, we will tell you where you can find a great website that provides regular updates on viewing conditions.
I-70 Corridor – If you’re looking for the easiest route, then this one is for you. Simply head west on I-70 about 110 miles to Avon. Between Vail and Avon, both sides of I-70 are lined beautifully with aspen.
Rocky Mountain National Park – One of the most popular summer destinations in the state is of course also a prime spot to view aspen in all their glory. Once in the park head toward Bear Lake. Glacier Gorge Junction provides a beautiful spot and you of course also get to enjoy all the splendor that Rocky Mountain National Park has to offer. Extend your viewing by taking Trail Ridge Road all the way through to the west side of the park and the Grand Lake and Granby area.
Peak to Peak Highway – This little road trip can be a dual purpose trip – gambling and fall foliage viewing! Take U.S. 6 through Clear Creek Canyon and then 119 through Blackhawk and Central City. You can of course stop there if your wallet is fat enough and donate some money to the casinos. From there continue on 119 toward Nederland. Take highway 72 toward Ward and Allenspark. There you will find more golden aspen than you can imagine, all with the Continental Divide nearby.
Poudre Valley Canyon – Heading north on I-25 take Colorado 14 west and into Poudre Canyon and Roosevelt National Forest. As you continue west you will come very near timberline as you come to Cameron Pass. Amazing views abound!
Guanella Pass – This is a nice, relatively short drive from Denver. From C470 take 85 through Bailey and Conifer, a nice drive unto itself. When you come to the town of Grant, take the Guanella Pass Scenic and Historic Byway north to Georgetown. The air is pretty thin along the way as you climb in excess of 11,500 views through the Pike and Arapahoe National Forests.
A couple other possibilities further from the Front Range:
Leadville / Aspen – From Denver take I-70 west to Copper Mountain and then Colorado 91 south over Freemont Pass to Leadville. Along the way there are plenty of viewing opportunities and Leadville is a nice little town to make a stop. From here you can take Highway 24 north back through Minturn and Vail. To extend the drive, take Highway 24 south to Colorado 82 and head toward Aspen. You can stop by the Maroon Bells in White River National Forest to view some of the most photographed mountains in Colorado.
Cottonwood Pass – From Denver take Highway 285 to Buena Vista. Head west on Main Street for seven miles then west on County Road 344 / Colorado 82. From there you start the climb up Cottonwood Pass with absolutely stunning views from the top. If you are up for it, you can continue down the west side of the pass into the Taylor Park area.
Honorable mentions worth considering:
If you do head out, be sure to send us your pictures for inclusion in our monthly photo slideshows!
For more information:
Our look back at this week in Denver weather history is somewhat shorter than normal owing to the fact that this time of year is usually relatively quiet. However, what is notable are some significant snowstorms, including one as recently as 1995.
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.
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.
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.
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.
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.
23
In 1873…north to northwest winds blowing almost a gale spread clouds of dust and sand into the city during the afternoon and evening. From the roof of the weather observer’s building…houses a few hundred yards away were not visible and not even the sky could be seen through the clouds of sand. The wind reached sustained speeds of 35 mph…but only 28 mph was registered for any one hour.
In 1977…wind gusts from 50 to 80 mph were reported along the foothills. A northwest wind gust to 53 mph was recorded at Stapleton International Airport.
23-24
In 2000…the first snowstorm of the season brought heavy snow to areas in and near the foothills. While the heaviest snow fell north of metro Denver…6 inches were measured in Boulder…4 inches at both Castle Rock and Morrison…but only 0.2 inch at the site of the former Stapleton International Airport where most of the precipitation fell as rain. At Denver International Airport where drizzle and rain fell on the 23rd… Snowfall during the early morning of the 24th was estimated at 2.1 inches due to melting. The foothills west of Denver received more snow with 10 inches measured at Conifer…9 inches 11 miles southwest of Morrison… 8 inches atop Crow Hill…7 inches at Chief Hosa…and 5 inches at Ralston Reservoir.
24
In 1901…northwest winds were sustained to 50 mph with gusts as high as 57 mph in the city.
In 1932…thunderstorm rainfall of only 0.11 inch was the only measurable precipitation for the month that year in the city.
In 1986…a very strong wind storm roared across metro Denver. Boulder was hit hardest. Winds peaked to 131 mph at the National Center for Atmospheric Research. This is thought to be the highest wind gust ever recorded in Boulder during September. A wind gust to 118 mph was clocked on Davidson Mesa and to 92 mph near Niwot. Gusts of 70 to 80 mph were common over all of Boulder where an estimated 70 to 90 large trees were uprooted. About a dozen of them hit cars. Two walls of a building under construction were toppled and solar panels were blown off a house. Traffic lights and power lines were downed. Damage to power equipment alone was estimated at 100 thousand dollars. Wind gusts to 87 mph at Jefferson County Airport damaged two planes. A woman was seriously injured in Boulder. She suffered a fractured skull when struck by a falling tree limb. Trees were also downed in Louisville and Lafayette. West wind gusts to 45 mph were recorded at Stapleton International Airport.
25
In 1873…a fire was sighted in the woods near Platte Canyon… Probably caused by high winds blowing sparks among the timber.
In 1896…an apparent cold front produced northeast sustained winds to 40 mph with gusts to 48 mph.
In 1910…a thunderstorm produced sustained north winds to 51 mph. This was the highest recorded wind speed in the city in September at the time.
In 1936…a vigorous cold front produced a deadly dust storm in the city. North winds sustained to 36 mph with gusts to 38 mph produced much blowing dense dust…greatly restricting the visibility. The temperature plunged from a high of 84 degrees to a low of 38 degrees by midnight. The weather observer described the event with the following. “at 6:00 pm the temperature was 82 degrees and the wind velocity was only 4 mph; but with the wind shifting to the north and the barometer rising quite rapidly…the temperature fell sharply. By 6:30 pm…the wind velocity increased rapidly and by 7:00 pm had reached a maximum sustained velocity of 36 mph…bringing with it clouds of dust which had been picked up by gale force winds in southern Wyoming and northern Colorado…covering the city. The visibility was generally reduced to about 1/4 mile; however…the whirling of the dust down the streets and alleys…the visibility was at times somewhat less. Airplanes were grounded…traffic was halted at times…and homes filled with dust. The strong winds damaged electric power and telephone lines…leaving homes in darkness for a few hours in the city and for 18 hours in suburban towns and putting 2500 telephones out of service because of broken lines. An electric lineman was killed while repairing damage by the high winds. The dust storm was followed by rain that began falling at 10:55 pm…which turned to snow during the early morning hours of the 26th. A major snow storm followed on the 27th through the 29th.”
In 1999…high winds developed in the foothills of Boulder County. Winds gusted to 90 mph at Wondervu.
Continue reading September 21 to September 27: This Week in Denver Weather History
Snow and cold? Temperatures well into the 90s? Tornadoes? Thunderstorms? Hail? Must be September in Colorado.
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.
10-17
In 2018…the high temperature equalled or exceeded 90 degrees for 8 consecutive days; breaking the previous streak of 7 consecutive days in the month of September.
10-18
In 2018…the high temperature equalled 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 minumum 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.
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.
15
In 1921…rainfall of 0.02 inch was the only measurable precipitation of the month.
In 1976…the public reported a funnel cloud and golf ball size hail east of Parker.
15-17
In 2000…unusually hot weather for so late in the season occurred when temperatures climbed into the 90’s setting daily record maximum temperatures on each of the 3 days. The high temperature was 92 degrees on the 15th and 95 degrees on both the 16th and 17th.
15-19
In 1906…rain on 5 consecutive days totaled 1.61 inches. A thunderstorm occurred on the 17th. High temperatures ranged from 48 degrees on the 16th to 65 degrees on the 15th. Low temperatures were in the lower to mid 40’s.
16
In 1874…a blast of west winds caused minor injuries during working hours in Boulder. In Denver…the winds veered suddenly from the southwest to the northwest around noon and increased to a maximum sustained speed of 49 mph behind an apparent cold front. The winds remained strong and backed to the west for the remainder of the afternoon.
In 2000…the record high temperature of 95 degrees at Denver International Airport established or equaled 3 different record extremes: the high temperature broke the previous record high for the day of 92 degrees set over a century ago in 1895; it marked the warmest that it has been so late in September; it also marked the 60th day during the warm season that the temperature had reached 90 degrees or more…equaling the record first set on September 29…1994.
In 2006…strong bora winds behind a pacific cold front raked the eastern slopes of the mountains and metro Denver during the afternoon. Northwest winds were sustained to 40 mph with gusts as high as 54 mph at Denver International Airport.
In 2007…a severe thunderstorm produced a peak wind gust of 67 mph…about one mile east of Bennett. At Denver International Airport…a peak wind gust of 48 mph was observed.
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In 1971…a record breaking early fall snow storm caused extensive damage to trees and utility lines. The heavy wet snow occurred with little wind…but caused record breaking cold temperatures for so early in the season. Snowfall totaled 15.6 inches at Stapleton International Airport with most of the snowfall…12.0 inches…occurring on the 17th. This was the heaviest first snow of the season. The maximum snow depth on the ground was 13 inches. Record low temperatures were set on three consecutive days: 31 degrees on the 17th…23 degrees on the 18th…and 20 degrees on the 19th…which was also a new all-time record minimum for the month at that time. Record low maximum temperatures were set on 4 consecutive days: 48 degrees on the 16th…35 degrees on the 17th…40 degrees on the 18th… And 42 degrees on the 19th.
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In 1873…brisk west to northwest winds at different times during the day…generally in sudden gusts…spread a good deal of dust into the city.
In 1953…strong winds caused thousands of dollars in damage to Boulder. The winds blew for most of the day with great gustiness…and a freak twister was reported during the afternoon. Damage was minor. A thunderstorm wind gust to 40 mph caused some blowing dust at Stapleton Airport.
In 1992…a tornado touched down briefly near Bennett. No damage was reported.
In 1993…severe thunderstorms rumbled across northern portions of metro Denver. Hail as large as 1 3/4 inches in diameter fell in Brighton. Dime size hail damaged several roofs of residences in Lafayette.
In 2000…for the second day in a row…the high temperature of 95 degrees at Denver International Airport broke three record temperature extremes: the high temperature broke the previous record for the day of 94 degrees set in 1895; it marked the warmest it has been for so late in the season; it also marked the 61st day in the year that the temperature had equaled or exceeded 90 degrees…eclipsing the record equaled the previous day and first set on September 29… 1994.
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In 1901…northeast winds were sustained to 42 mph with gusts to 50 mph behind an apparent cold front.
In 1948…the low temperature cooled to only 69 degrees…the all-time record high minimum for the month.
In 1988…a strong cold front blasted metro Denver with high winds. Gusts reached 82 mph in Longmont and 81 mph at Jefferson County Airport near Broomfield where the winds flipped over and destroyed a small airplane. Wind gusts to 60 mph were recorded in Boulder and Wheat Ridge. West wind gusts to 54 mph were clocked at Stapleton International Airport. The strong winds downed trees and power lines and damaged homes and cars. A Longmont man was slightly injured…when a tree fell on top of his car.
In 1990…a slow moving thunderstorm over southwest metro Denver spawned an ominous looking funnel cloud near the intersection of Sheridan Blvd. and U.S. Highway 285. The funnel cloud nearly touched down a few times before lifting back into the main cloud. No damage was reported. Pea to marble size hail and 3/4 inch of rain fell over central and northeast Denver. Numerous streets and underpasses became flooded on Denver’s south side when the heavy runoff backed up storm sewers. Thunderstorm rainfall totaled 1.02 inches at Stapleton International Airport.
In 1993…a severe thunderstorm rolled through southeast metro Denver. Dime size hail was reported in many areas. Straight-line winds from the thunderstorm…measured by a weather spotter at 70 mph…tore the roof off 6 apartments of an apartment complex in Aurora. Heavy rain which accompanied the winds caused major damage to the apartments as well as the contents. Many trees…fences… And power poles were knocked down by the strong winds. Heavy rain flooded roadways in Denver and Aurora. Thunderstorm rainfall totaled 1.08 inches and north winds gusted to 44 mph at Stapleton International Airport where the visibility was briefly reduced to as low as 1/4 mile in heavy rain.
In 1996…a late summer snowstorm struck the northern mountains and Front Range eastern foothills. Golden Gate Canyon received 6 inches of new snow with 5 inches reported at both Nederland and Blackhawk. Thunderstorms produced heavy rain across metro Denver…which was mixed with snow by late evening. Rainfall totaled 0.83 inch at the site of the former Stapleton International Airport and 1.22 inches at Denver International Airport where northwest winds gusted to 39 mph.
Continue reading September 14 to September 20: This Week in Denver Weather History
As a transition month, September can bring a wide variety of weather conditions as we see in our look back at this week in Denver weather history. From summer-like heat to snow and wildfires to tornadoes, just about anything can happen.
From the National Weather Service:
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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In 1933…heavy rain over the Cherry Creek…plum creek…big dry creek…and little dry creek watersheds caused flooding on the South Platte River in Denver overnight. Nearly an inch of rain…0.98 inch…fell in the city.
In 1944…a trace of rain fell on each day. This together with a trace of rain on the 4th and 30th was the only precipitation for the month. The total of a trace of precipitation for the month equaled the driest September on record first set in 1892.
In 1994…unusually very warm weather resulted in three temperature records being equaled. High temperatures of 94 degrees on the 9th and 93 degrees on the 10th equaled record maximums for the dates. Low temperature of 63 degrees on the 9th equaled the record high minimum for the date.
Continue reading September 7 to September 13: This Week in Denver Weather History
A recurring theme from most of 2025 for August. Thornton once again saw temperatures above normal and precipitation below, something that has happened far too often this year.
Above normal temperatures dominated the first three weeks of the month. Mercury readings in the 90s were common with only three days being below that mark. Precipitation was absolutely scarce with a mere 0.01 inches being recorded during the first 21 days of the month.
Thankfully, Mother Nature took mercy on us for the last 10 days of August. We saw temperatures cool a good bit with every day seeing below average readings. While precipitation wasn’t great, she also was kind enough to finally give us a couple days with much-needed rain.
Temperatures in Thornton came in at an average of 72.6 degrees for the month. This was a good bit above the 19-year running average for August of 71.8 degrees. It was also the sixth month in a row for Thornton with above average temperatures.
Out at DIA where Denver’s official records are taken, it was a good bit warmer. The Mile High City saw an average of 73.8 degrees for August 2025. This was above their long term average for August of 72.9 degrees.
In terms of precipitation, Thornton ended up with 0.51 inches in the bucket. Virtually all of that fell in the last seven days of the month. It was well below our running August average of 1.20 inches.
For Denver, they saw two days with thunderstorms that dumped a great deal of rain on the airport, storms that missed us. As a result, their rain total for the month was a surprising 4.12 inches. This was well above their long term average for August of 1.58 inches.
Click here to view Thornton’s complete August 2025 climate summary report.
