413
FXUS65 KBOU 121819
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1219 PM MDT Sun Oct 12 2025

.KEY MESSAGES...

- Windy with a quick shot of snow over the northern mountains this
  morning.

- Dense fog over much of Weld and Morgan counties early this
  morning.

- Precipitation chances return late Monday across the mountains
  and plains.

- Above normal temperatures expected mid-week.

&&

.UPDATE...
Issued at 429 AM MDT Sun Oct 12 2025

Dense fog developed in low lying/colder areas of Weld and Morgan
counties early this morning. Webcams show visibilities down to 100
yards or less along US 34 and on US 85 south of Greeley. The
approaching front should dissipate this by mid morning.

Speaking of which, there`s a substantial batch of showers, along
with wind gusts of 40 to 50 mph, along the front just entering our
area from the west. The snow level will drop in the showers, it`s
even down to 32 degrees at Craig, so much of Jackson, Grand, and
Summit counties will have a quick shot of wet snow over the next
few hours. There shouldn`t be much impact across most of this
area, but it may be cold enough over the passes for some slush and
also low visibility in the heavier showers. Main impact to I-70 in
Summit county should be between 5 and 8 am.

Also, it looks like it should get cold enough for at least patchy
frost tonight in the colder areas of Weld and Larimer counties.
There`s some question about cloud cover and a little wind further
south and east, but there`s some threat for Morgan and Logan
counties and the colder low spots from Douglas county out to Limon
as well. We`ve posted a frost advisory for Weld and Larimer
counties where the threat is greatest. It still looks like it
should just be the colder spots and not widespread, and not a sure
thing.

Other minor changes include higher PoPs this morning for the
current shower band and more cloud cover although it`s not clear
how much will survive east of the mountains, nor how quickly and
how far north the warm advection clouds coming up from the south
tonight and Monday will develop.

&&

.DISCUSSION /Through Saturday/...
Issued at 220 PM MDT Sat Oct 11 2025

Current radar shows scattered light showers over the mountains and
plains, which will end this evening as an upper level shortwave
reaches Colorado. With tropical moisture being advected into our
region, snow levels will stay above 12,000 feet. We have been slow
to warm up across the western/northwestern plains today as a
surface lee trough has formed, keeping the warmer southeast winds
to the east of the low. Current observations show temperatures in
the mid 60s closer to the foothills, while the farther eastern
plains have already reached mid to high 70s. With the expected
cloud cover through this evening, temperatures most likely will
stay in the 60s for the majority of the plains.

There will be a lull in precipitation across the mountains and
plains tonight. Just before sunrise, the upper level shortwave
will travel across Wyoming and advect cold air into our region,
along with providing enough forcing for precipitation across the
higher terrain. 700-mb temperatures should get down to -2 to -4
dg C, which would support snow levels above 8500 feet. Expect 1-4"
along the western slopes of the Park Range and Front Range
mountains by early Sunday afternoon. In addition, with cross-
barrier flow of 30-40 kts. winds could gusts up to 50 mph at the
highest peaks, which will make blowing snow likely through early
Sunday afternoon.

For the plains, downsloping winds should keep conditions dry on
Sunday. A well-defined cold front will arrive sometime in the
morning, bringing wind gusts up to 45 mph in the northern plains.
With minimum relative humidity values between 20-25%, elevated
fire weather conditions are possible in the north and northeastern
plains.

Monday will be cooler behind the cold front, with max
temperatures in the low 60s across the plains and 40s-50s in the
higher terrain. With south/southwest flow aloft, warm air
advection will aid in light showers across the forecast area. As
of right now, NBM looks sufficient in the spatial extent of PoPs,
with best chances of precipitation across the mountains and
eastern plains.

Around mid-week, we will continue to be under southwest flow
aloft due to an upper level low forming over California and a
ridge building over the southern United States. At the surface,
southerly winds will bring warmer and drier conditions, with
temperatures expected to be 10-15 degrees above seasonal normals.

By the end of the week, the upper level trough will travel northeast
from California and track into Wyoming. However, there is still
model variability in terms of track, evolution, and intensity of the
low. Some ensemble solutions favor a piece of energy breaking from
the main trough and traversing Colorado, which would bring
precipitation chances back to the mountains and plains by Thursday.
Will continue to monitor the situation.

&&

.AVIATION /18Z TAFS through 18Z Monday/...
Issued at 1151 AM MDT Sun Oct 12 2025

VFR conditions expected through the TAF period. Gusty westerly
winds have finally set in across KDEN and KBJC late this morning.
With the gusty NW winds in place off the Cheyenne Ridge, an
anticyclonic wind pattern has developed across the plains which
is keeping KAPA winds light and northeasterly. Expecting gusty WNW
winds to persist at KBJC/KDEN through the afternoon before
gradually diminishing through the evening. Winds at KDEN are
expected to settle into the SSE for the overnight hours and
continuing through the TAF period, with increasing gusts beginning
around 14/15Z Monday morning.

There is low confidence in the winds at KAPA for this afternoon,
as there is potential for a shear zone to move across the field
keeping the northeasterly winds in place on its northern edge, and
bring WSW winds in on its southern edge. If the boundary stays to
the south, winds will likely stay northeasterly, but if it moves
more north, we can expect winds to become WSW. Have introduced a
TEMPO to account for this between 21-24Z. There is far more
agreement in guidance and higher confidence in winds past 0Z, with
an easterly turn expected before settling into the SSE for the
overnight through the rest of the TAF period.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 2 AM to 8 AM MDT Monday for COZ038-042-043.

&&

$$

UPDATE...Gimmestad
DISCUSSION...MAI
AVIATION...999

NWS BOU Office Area Forecast Discussion