171
FXUS65 KBOU 062203
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
303 PM MST Sat Dec 6 2025

.KEY MESSAGES...

- Mountain snow tapers off through this evening, but strong winds
  will sustain some blowing snow at higher elevations/pass levels.

- Sunday through Tuesday: Windy, with near-seasonal temperatures.
  Mostly dry, save for some light mountain snow showers at times.

- Another system may bring renewed mountain snowfall Wed-Thu, with
  a lower but non-zero chance of precipitation for the lower
  elevations. Strong winds will continue.

&&

.DISCUSSION /Through Saturday/...
Issued at 201 PM MST Sat Dec 6 2025

After an eventful first half of the day which featured some
impressive 2"/hr snowfall rates in our mountains from a few midday
bands, things are steadily calming down on the snowfall front.
Upstream water vapor imagery shows modestly drier air that will
gradually make its way into the high country. Along with a
weakening in both flow aloft and mid-level lapse rates, snow
showers will become considerably lighter and more intermittent
through the remainder of the day, focusing mainly on our higher
mountain slopes. As such, felt comfortable dropping the winter
weather headlines for several zones (Park Range, plus North/Middle
Parks), where wind speeds will also diminish. For now, will retain
the Winter Storm Warnings for our Front Range/Summit County
mountains, as wind speeds will take longer to taper off. As of
this writing, we`re continuing to see gusts consistently hitting
55-80 mph across the higher peaks and passes, so blowing snow
impacts are likely to continue regardless of additional snowfall.
Across the plains, mid-level moisture has been sufficient to
allow for a few bands of mixed wintry precipitation with the
trough axis, although these should dissipate as we enter the
evening hours.

Tonight, a weak backdoor cold front will slide into the plains as
surface high pressure gains prominence over the northern CONUS.
With that, we could see enough low-level moisture advection and
radiational cooling to allow for patchy fog development across
portions of our E/NE plains, so have introduced a mention of this
into the forecast. This will also give way to marginally cooler
temperatures on Sunday. Most areas will remain dry, with ample
sunshine for the lower elevations and some continued breezy
conditions. Modest westerly flow in the high country and lingering
low-level moisture will keep the chance of light snow showers
going there, mainly through the morning hours and above 9,000 ft.

The picture will be rather unchanged for Monday, with a few light
orographic snow showers in the forecast for our mountains and
continued breezy conditions near ridgetops. The lower elevations
should see some slight warming under a subsident flow regime,
breaking into the lower 50`s for most areas.

We won`t be able to escape the topic of wind as we look ahead at
the midweek timeframe - in fact, much to the contrary. Reminds me
of my husband blowdrying his hair every morning...it seemingly
never ends. But I digress...

Models are in relative agreement in showing an embedded shortwave
developing over the northern plains, driving a healthy NW-SE
oriented jet southward into Colorado through the day. Surface
pressure gradients look quite impressive, with some of our
stronger GJT-DEN Sangster-derived gradients peaking around 16-18
mb. Together with modest but widespread QG subsidence, many of the
initial ingredients are there to propel significant winds across
our high country, foothills and, potentially, adjacent lower
elevations if factors align properly. It`s a little too early to
discern finer details such as the propensity for any stable or
critical layers etc., but have nonetheless raised our forecast
winds for the midweek period above NBM guidance. Whilst Tuesday`s
wind looks to carry more of a Chinook flavor, it appears more
Bora-driven for the Wednesday/Thursday period, with ensemble
guidance indicating the passage of another shortwave to our north
and a more substantial front to go along with it. Confidence is
thus a little higher when it comes to gusty winds being more
widespread Wednesday and Thursday. To boot, the ECMWF`s EFI
indicates 80-90th percentile wind gusts Tuesday through Thursday (relative
to rolling 5-week climatology), a clear signal for mountain high
winds at the very least.

There`s notable uncertainty in the track of this feature still,
which will dictate precipitation potential (particularly for the
lower elevations), however all but a small subset of ensemble
members would keep our mountains dry. Anywhere from a few inches
of localized snowfall to another significant mountain snow event
would be on the menu, and only time will tell where on that
spectrum we`ll end up. With hefty northwest flow aloft and hints
at quite robust frontogenesis with this shortwave, it`s a pattern
that could lend itself to some surprises, even for the urban
corridor and plains. Apart from a slight increase to PoPs for the
lower elevations for the above reasons, saw no reason to deviate
much from current NBM guidance given the ongoing uncertainty.

&&

.AVIATION /18Z TAFS through 18Z Sunday/...
Issued at 1046 AM MST Sat Dec 6 2025

Challenging forecast for the next six hours or so, until 00Z
Sunday. Northwest low level flow has produced an anti-cyclone with
north to northeast winds moving into DEN. This should decrease
the downslope component some and scattered showers will be
possible this afternoon. Expect winds to stay a northerly
direction (NW, N, or NE) through 00Z Sunday. Outflow from the
showers could produce gusts to around 30 knots. Expect the showers
to be mostly rain. A stronger shower could briefly produce snow
or graupel. Ceilings could fall to 5000-6000 feet under the
stronger showers. Winds are expected to become weaker after 00Z
Sunday and settle a southerly direction by 06Z.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 11 PM MST this evening for COZ033-034.

&&

$$

DISCUSSION...BRQ
AVIATION...12