219
FXUS65 KBOU 022248
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
348 PM MST Tue Dec 2 2025

.KEY MESSAGES...

- First winter storm of the season remains on track for the Front
  Range and I-25 corridor. Impacts to the Wednesday morning
  commute likely, with some impacts lingering into the afternoon
  and evening hours.

- Milder to end the week, but strengthening winds and increased
  potential for heavier and prolonged mountain snowfall into the
  weekend.

&&

.SHORT TERM /Through Wednesday/...
Issued at 326 PM MST Tue Dec 2 2025

Zonal flow is in place across the forecast area today, ahead of a
weak, positively tilted shortwave swinging across the
intermountain West this afternoon. That wave is expected to shear
out a bit as it tracks towards the NV/UT border by Wednesday
morning... eventually reaching northern Arizona by 00z Thursday.

From a pattern standpoint, one would think that this storm track
would not produce a favorable setup for a Front Range snow
event, given how far away the primary shortwave (and its
associated QG ascent) are from our CWA. However, there`s still
enough going for this storm that we`ve got a meaningful snowfall
to discuss. Let`s dive in.

A cold front is expected to push into the region during the
early overnight hours. There`s also much better near surface
moisture behind the front, with mid 20s to low 30s dew points
noted across northern Wyoming and Montana/South Dakota this
afternoon. As the mid-level low circulation drifts into western
Colorado, upslope flow should start to deepen, with generally
10-20kt magnitudes through 700mb. Guidance has broadly trended
towards developing precipitation a little earlier in the overnight
period tonight, which has led to a modest increase in snow amounts
prior to daybreak Wednesday. Some high resolution guidance
including the past several cycles of the HRRR have been quite
aggressive in developing snow prior to 12z... which is one of the
few remaining questions marks with this storm.

Snow should be fairly widespread across the region by daybreak
Wednesday, which should continue into the morning commute. With
BUFKIT soundings suggesting most of the lift intersecting with the
dendritic growth zone, efficient snow ratios appear likely during
the majority of the morning commute across most of the foothills
and Denver metro/I-25 corridor. There is some uncertainty with
regard to how far north/east the snow spreads towards places like
Fort Collins/Greeley/DIA/Limon, with much higher confidence closer
to the base of the foothills. Snow should gradually taper off
from north to south through the day, with most locations seeing
the end of accumulating snowfall near/before 00z.

Model guidance is in remarkably good agreement today, with trends
today generally increasing QPF by 0.1-0.2" across the Denver
metro. Our deterministic forecast is very close to the ECMWF
ensemble mean through 12z Thursday, with a gradient of 0.25-0.6"
across the Denver metro into the foothills. With the University of
Utah`s SLR algorithm suggesting ratios of around 12-14.5:1 this
would translate to around 3-7" of snow across most of the metro,
with higher totals likely in the lower foothills. A few HRRR runs,
along with some NSSL/GSL MPAS-core guidance has also hinted at a
ribbon of enhanced (0.7-1") QPF in the lower foothills where
localized totals of up to a foot appear feasible. Unsurprisingly,
our snowfall totals were nudged up an inch or two with this
forecast package.

Translating this to impacts... not a whole lot has changed to our
thought process over the last 12-24 hours. With snowfall rates
maximized during the early half of the morning commute, travel
issues appear likely across the region... especially since this is
the first winter driving experience for many this year. Travel
impacts are expected to linger through the day into the Wednesday
evening commute, especially if snow does hold on a little longer
than expected. The main change of note today was to add in the
northern foothills/I-25 corridor and South Park into the advisory
given the recent trends to the snowfall forecast.


&&

.LONG TERM /Wednesday night through Tuesday/...
Issued at 326 PM MST Tue Dec 2 2025

These new winter-feeling vibes will continue through the long term
forecast period (at least across the mountains!) as persistent
northwesterly flow returns behind the exiting shortwave Thursday
night. While the brunt of the snowfall will be behind us by Thursday
evening, light snow will remain, gradually diminishing from north to
south across the forecast area through Thursday night as upslope
flow comes to an end. The evening commute could see some snarls,
with the areas of most concern for slick conditons to generally be
along and south of I-76. Cold temperatures are expected overnight as
outgoing moisture allows for clearing skies. Mountain valleys will
be cold, dropping below zero, while the plains and foothills will
range from the single digits in our typical colder spots, to the mid
to upper teens along the foothills and adjacent plains.

Dry conditions are expected on Thursday, with initiation of a
gradual warming trend that will continue through the extended
forecast period. Colorado will be on the eastern side of a broad
ridge that will be situated over the western CONUS for the
foreseeable future. Northwesterly flow is notorious for allowing
moisture and shortwaves to drop southeastward out of the Pacific
Northwest and into the forecast area, and this setup looks no
different. We are expecting multiple waves of additional snowfall
for the high country through the weekend, with the northern
mountains generally more favored in this northwest regime.

By Thursday night, a weak shortwave is expected to move across the
Rockies that will bring some of that aforementioned moisture from
the Pacific into the mountains. Northwesterly flow will gradually
increase through Friday keeping orographic snowfall going through
the day. Light accumulations are expected, mainly for the highest
elevations of the Front Range Mountains, with the greatest
amounts expected for the Park Range through Friday. The lower
elevations are expected to remain dry.

For the weekend, ensembles are in wide agreement that a more notable
snowfall is slated to slide into the mountains with a more potent
shortwave and upper-level jet moving into the forecast area. This
will be our greatest shot at seeing moisture across the lower
elevations, albeit low chances, with ensemble members holding at
around 30% showing any QPF east of I-25. Winds will increase across
the higher elevations as well as the plains, with tightening
pressure gradients and lee troughing centered over the Texas
panhandle. This is still a ways out and will need to lock in more
details as we get closer, but this more active pattern is certainly
starting to feel more like winter is finally here.


&&

.AVIATION /18Z TAFS through 18Z Wednesday/...
Issued at 1119 AM MST Tue Dec 2 2025

VFR conditions expected through this evening before lower ceilings
and reduced visibilities arrive by 06Z/07Z as a disturbance will
bring snow to all TAF sites. However, conditions could deteriorate
as early as 03Z/04Z with scattered snow showers ahead of the main
system. Have added a PROB30 for DEN and APA for that reason. IMC
conditions are expected with the arrival of snow, with ceilings
and visibility dropping to IFR, and LIFR possible for APA and BJC
Wednesday morning. Heaviest snow rates and worst
visiblities/ceilings (up to 0.5"/hr and briefly 1"/hr for APA and
BJC) are likely between 10Z and 14Z, before a gradual improvement
to MVFR conditions through 18Z. After that, snow will slowly
decrease to scattered snow showers through 00Z.

Total snow accumulations are still most likely 2-4" at DEN, and
3-5" at BJC and APA. Temperatures will drop to freezing or below
freezing by 00Z this evening, so expect snow to accumulate on
paved surfaces.

In terms of wind, generally light (<10 kts) N to NE winds for DEN
and APA with a gradual turn to SE this evening. Then, with the
arrival of a cold front, winds will transition back to ENE. There
is a chance (~20%) for downsloping winds to briefly reach DEN
between 18Z and 23Z, where 10-15 kts is possible. Most likely,
those westerly winds will stay south of the airport. For BJC,
westerly winds generally under 15 kts will continue for the next
couple of hours before turning light and VRB this afternoon.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from midnight tonight to 6 PM MST
Wednesday for COZ035-036-039>041.

Winter Weather Advisory from 2 AM to 8 PM MST Wednesday for
COZ037.

Winter Weather Advisory from midnight tonight to 2 PM MST
Wednesday for COZ038.

&&

$$

SHORT TERM...Hiris
LONG TERM...9
AVIATION...MAI