835
FXUS65 KBOU 012248
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
348 PM MST Mon Dec 1 2025

.KEY MESSAGES...

- Gusty winds expected along the eastern slopes of the Front Range
  Mountains late tonight into Tuesday morning.

- Light snow showers return to the mountains Tuesday, with high
  temperatures warming to near normal levels.

- First notable snowfall of the season increasingly likely for the
  urban corridor Wednesday, impacting Wednesday morning commute.

- Milder to end the week, with strengthening winds and increased
  potential for additional and more prolonged mountain snowfall
  into the weekend.

&&

.SHORT TERM /Through Tuesday/...
Issued at 305 PM MST Mon Dec 1 2025

Current satellite water vapor imagery shows dry conditions in place
across Colorado today. Despite sunny skies, observations show
temperatures remain in the 30s across the vast majority of the lower
elevations, with only a few readings climbing into the 40s observed
near the base of the foothills and adjacent plains, and along the
South Platte River Valley. The mountains have warmed into the 20s
where they are expected to remain through the afternoon.

Looking upstream, water vapor imagery also shows our next
approaching system currently moving across the Pacific Northwest and
expected to slide a shortwave southeast across the Intermountain
West through the day Tuesday. As this system approaches, cross-
sections show northerly winds aloft are on track to transition to
the west through tonight, bringing increasing cross barrier flow
along the Front Range Mountains. A mountain wave is likely to
develop sometime overnight tonight, with gusty winds between 25-35
kts expected to spill down the eastern slopes of the Front Range,
with some stronger gusts possible in our typical windy spots in the
foothills of Boulder County, and up to 55 kts along ridgetops. One
upside to the downsloping winds will be the compressional warming
that comes along with them. This will help keep overnight low
temperatures slightly warmer for those who live in the foothills and
along the adjacent plains tonight. While overnight low temperatures
are forecast to be widespread teens across the plains, and single
digits in the mountains and valleys, we can expect at least a ten to
fifteen degree warming effect for the aforementioned areas near the
foothills.

Snow is expected to begin in the northern mountains early Tuesday
morning as upwards ascent begins to increase ahead of the
approaching shortwave. With the latest hi-res guidance trend showing
increased QPF values across the Medicine Bow, Park Range, and Indian
Peaks this afternoon, have bumped up totals through the day Tuesday
for this forecast package. This will lead to slick travel
conditions developing throughout the day, especially for the high
mountain passes. Afternoon temperatures are expected to warm to
near normal values across the plains ahead of the long awaited
widespread snowfall expected to slide eastward onto the plains
Tuesday night. See below for more details.

&&

.LONG TERM /Tuesday night through Monday/...
Issued at 305 PM MST Mon Dec 1 2025

Had to rub my eyes a few times to make sure it wasn`t fiction, but
here we are less than 36 hours from the onset of our next system,
and we`re remaining steadfast in our forecast of a few inches (not
tenths of an inch!) of snow for much of the urban corridor for
the first time this season. So what`s brewing?

A shearing shortwave still looks to detach from it`s parent
trough Tuesday night and descend southward over the Four Corners.
QG fields indicate broad ascent associated with this feature and
overspreading Colorado through Wednesday. Latest guidance has
continued to accelerate the low`s progression, albeit slightly,
thus moving up the onset of wintry precipitation to shortly after
midnight Tuesday night for areas east of the Continental Divide.
Low-level (850-700mb) frontogenesis looks healthy for the morning
hours, and there`s relatively good consensus when it comes to a
period of 6-12 hours of predominantly northeast upslope flow below
700mb centered on the first half of the day. Variability still
exists as far as the duration of any upslope, whether or not we
may see intrusions of more easterly winds (some of the recent CAMs
would support this), and to a lesser extent the speed of the
shortwave as it looks to merge back with the broader flow
pattern, which will undoubtedly lead to additional fine-tuning of
snowfall amounts and distribution. Nevertheless, confidence has
grown with regard to most of the Denver metro, southern foothills
and Palmer Divide receiving at least 2" of snow (75-85% chance),
with the heaviest of the snowfall coinciding with the morning
commute.

With this in mind, have issued Winter Weather Advisories for
these locations in anticipation of the difficult road conditions
that will result, regardless of exact amounts. Highlights may need
expanding into the mountains and/or farther north depending on
the trend in upsloping characteristics over the coming forecast
shifts. With there being greater alignment now among ensemble
systems (the previously lighter GEFS has shifted closed to
ECMWF/Canadian solutions), total QPF of 0.2-0.4" looks reasonable
for a large portion of our urban corridor, foothills and
mountains, with a focus in the aforementioned areas. With snow
ratios anticipated to near 15:1 much of the time, felt
comfortable trending the forecast snowfall totals a little higher,
with areas of 3-6" appearing increasingly likely, and potential
for localized higher totals closer to the base of the foothills.
Snow will look to taper off quickly through the latter half of the
day as surface winds veer to the south, giving way to a mostly
sunny but cool day on Thursday.

Friday and into the weekend, the pattern will be dominated by
strengthening northwest flow aloft on the NE periphery of a high
pressure region over the eastern Pacific. Moisture embedded in
this flow looks to impinge on the high country as early as Friday,
when we have a few orographic snow showers in the forecast for
the higher elevations. Meanwhile, our lowlands should see dry and
milder conditions. The bulk of the moisture should hold off until
the weekend however, associated with one or two weak shortwaves
and a strong upper-level jet. Such a pattern would be conducive to
a more extended period of mountain snowfall which could be heavy
at times, favoring the northern mountains (i.e. Park and Medicine
Bow Ranges) in particular, but impacting most/all of our mountain
zones at some point or another - a pattern chance which is sorely
needed in this region. Wind will be the other aspect to watch
during this timeframe, with breezy conditions likely to become
more widespread, as well as an opportunity for some
downslope/mountain wave enhancement around Saturday. The lower
elevations do still have another window for wintry precipitation
over the weekend, but it`s much less set in stone compared to our
mountains and will depend on the evolution of any embedded
shortwaves that do develop.

&&

.AVIATION /18Z TAFS through 18Z Tuesday/...
Issued at 1017 AM MST Mon Dec 1 2025

VFR conditions expected through the TAF period. Current winds are
light and variable across the TAF sites this morning. Expecting a
transition to the NE by around 19Z for KDEN/KAPA, with variable
winds continuing slightly longer at BJC. Winds should transition
to the southeast ahead of the normal diurnal pattern as
anticyclonic flow persists off the Cheyenne Ridge.

There is still some uncertainty with winds at KBJC overnight
tonight, as mountain wave enhancement is expected to allow for
some gusty westerly winds to push into the airfield. Some of the
hi-res guidance suggest winds could gust as high as 40 kts once
the mountain wave forms. Have kept a TEMPO for now, but
confidence in timing is low at this time. If the gusts do make
their way that far east, there is about a 20% chance they persist
past the TEMPO time frame, and the current VRB winds may not
develop as stated in the current TAF, as the gusty westerly winds
may hold on while the wave remains.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from midnight Tuesday night to 6 PM MST
Wednesday for COZ036-039>041.

&&

$$

SHORT TERM...9
LONG TERM...BRQ
AVIATION...9