000
FXUS65 KBOU 030326
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
826 PM MST Sat Dec 2 2023

.KEY MESSAGES...

- Mountain snow and winds will increase tonight.

- Moderate to heavy snow and significant blowing snow are expected
  to produce very difficult travel conditions in the mountains
  tonight and Sunday morning.

- Strong winds are expected to develop across the mountains and
  higher foothills tonight and continue into Sunday night, with a
  few gusts greater than 75 mph possible.

- Late Monday through Thursday will be mild and dry.

- The next system to potentially impact Colorado will arrive
  late Thursday night through Saturday. Mountain snow and colder
  temperatures are likely but impacts across the plains remain
  uncertain at this time.

&&


.UPDATE...
Issued at 804 PM MST Sat Dec 2 2023

A strong northwesterly flow aloft is over the forecast area,
between one system exiting into the Central Plains, and another
approaching from the northwest. Currently, we are under a regime
of weakening QG descent in the wake of the first system. Latest
highway cameras are filling up with snow this evening. That next
system will shift eastward overnight as weak to moderate mid/upper
level QG ascent develops overnight, coupled with strong
orographic ridgetop winds. The nose of a 110 kt upper level jet
sits over northwest CO by 12z Sunday, then translates eastward as
well. Strong downslope winds still expected to develop this
evening, with the best wave amplification until 09z, before it
starts to shear out and break down. For Sunday, strong bora wind
coupled with the upper level jet, and another dose of mid/upper
level QG descent that will continue into Sunday afternoon. Overall
no changes to the ongoing highlights, with the heaviest snowfall
expected to occur from 06z tonight through 18z on Sunday.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 236 PM MST Sat Dec 2 2023

Water vapor satellite imagery showing this morning`s trough
spinning over western Nebraska at this time. Best subsidence is
over eastern Wyoming and northeast Colorado with the mountains
seeing more favorable conditions for snow. Looking at a variety of
data (satellite, radar, observations, web cameras) appears snow
has mostly ended or decreased to flurries in the valleys with
light snow lingering over the mountains. Most roads have at least
partially thawed in the mountains due to insolation and light
snowfall rates. This is expected to quickly change by early
evening with the loss of sunshine and snowfall increasing. The
next wave which will be stronger is off to the northwest over the
Pacific Northwest. Widespread clouds and snow are ahead of it,
with radar showing widespread snow over northern Utah and eastern
Idaho. Appears we are still on track heavy snow and windy
conditions in the mountains late tonight and Sunday morning.
Travel is expected to become very difficult in the mountains by
Sunday morning due snow and blowing snow with only a slow
improvement through the afternoon. Cross sections show moisture
slowly shallows through the afternoon which should cause snow to
become light, though they may be another uptick in snow Sunday
evening.

For areas east of the mountains, windy conditions are expected
tonight and Sunday. The HiRes models show a surge of stronger
winds traveling down the foothills this evening, likely associated
with a mountain wave, which doesn`t last long. Windy conditions,
possibly strong, reform (or could continue through the night due
to strong winds just off the surface) Sunday morning as the trough
pushes through the region. The strong winds are expected to
continue in the higher foothills and mountains through Sunday
evening. A few snow showers could move off the higher terrain
Sunday morning. If they survive, snowfall will be light with only
a dusting at most expected.

.LONG TERM...(Sunday night through Saturday)
Issued at 236 PM MST Sat Dec 2 2023

A shortwave trough will be exiting Colorado quickly on Sunday
night as it heads southeastward. On the backside of this trough
there will be a wave of deeper moisture that moves across the
northern mountains. This will re-intensify snow showers in the
mountains and moderate snowfall will occur in the Park Range and
northern Front Range mountains. Winter weather highlights continue
through 11pm Sunday night and it is possible the highlights could
be extended a few more hours. Warm air advection will be ongoing
in the low levels Sunday night. This will strengthen an inversion
over the foothills and adjacent plains and will likely allow for
a stronger mountain wave to develop and for winds aloft to be
pulled towards the surface in the foothills and adjacent plains. A
High Wind Warning was issued for the foothills and depending on
the strength of the mountain wave, it could be extended to last
through much of Sunday night. Winds gusts up to 70-80 mph can be
expected.

Strong northwesterly flow aloft will continue on Monday with drier
air moving into Colorado. Snow showers will come to an end by the
afternoon and winds will begin to relax during the evening hours.
The warm air advection will allow for temperatures to warm to the
mid to upper 50s across the plains.

Colorado will be rid of the troughing and northwesterly flow on
Tuesday as a board ridge aloft moves overhead. This will lead to
mild and dry conditions with much lighter winds than previous
days. Highs will reach the 60s in the spots across the plains.

The ridge will continue to impact weather across Colorado on
Wednesday and Thursday. This will lead to gorgeous weather for early
December as highs across the plains will reach the mid to upper 60s.
The record highs for Denver on Wednesday and Thursday are 73 and 70,
respectively. Those will likely be be just out of reach but the
Thursday one could be a close call.

Models are in agreement that a trough will move over the
Intermountain West on Friday and towards Colorado on Saturday. What
models don`t agree on is the intensity and exact location of this
trough. Ensembles show that there is a good chance the plains will
see some snow with this system but they are all over the place
with regards to amounts. This system will have to be watched as
there is a small chance it brings a widespread, moderate to heavy
snow. There are two things that models have higher confidence
with for this system. Those are a healthy snow for the mountains,
and colder weather for all areas with the single digits to teens
expected.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 509 PM MST Sat Dec 2 2023

VFR conditions expected tonight and Sunday. Winds at DEN/APA
are light and variable and will transition to southerly 01-02z,
increasing after 06z out of the SW at 10-15 kts. BJC will likely
be impacted by the enhanced downslope winds off the foothills
early Sunday morning with gusts 35-45 kts with the highest gusts
likely in the 06-12z timeframe.

Wind shifts at DEN/APA will be a challenge Sunday morning. Winds
could stay more westerly through late morning then transition to
NW in the afternoon, or they could transition more quickly mid-
morning. There is a low chance for gusts above 25 kts. There is
also the potential for a brief isolated snow shower in the
morning, in the 13-17z time frame. If this occurs, brief
reduction in visibility and lower ceilings (MVFR) could be
possible. But this is a low probability occurrence. The wind late
in the afternoon should again decrease with the gusts subsiding by
23z.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 11 PM MST Sunday for COZ030-032.

Winter Storm Warning until 11 PM MST Sunday for COZ031-033-034.

High Wind Warning until 11 PM MST Sunday for COZ035-036.

&&

$$

UPDATE...Cooper
SHORT TERM...Meier
LONG TERM...Danielson
AVIATION...Cooper

NWS BOU Office Area Forecast Discussion