000
FXUS65 KBOU 021824
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1124 AM MST Sat Dec 2 2023

.KEY MESSAGES...

- Mountain snow and winds will increase tonight with areas of
  moderate to heavy snow and significant blowing snow creating
  very difficult travel Saturday night 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.

&&

.UPDATE...
Issued at 956 AM MST Sat Dec 2 2023

Going forecast to on track with widespread snow falling across
the mountains. Lift from this first wave is about to shift off to
the east and snow is expected to become light and end in places
this afternoon. This lull will be short lived as snow increases
this evening as the next wave approaches the Central Rockies. Did
some fine tuning to PoPs and QPF, but no major changes were made
to PoPs and snowfall amounts.

As far as the High Wind Watch goes, it is still unclear if we see
high winds (75 mph or greater) tonight and/or Sunday. Mountain
wave set up isn`t great, though the NAM shows a brief mountain
with a stable layer and reverse wind profile centered around 06Z
Sunday. Taking a step back and looking at the bigger picture, one
would think the biggest threat for high winds would occur with
subsidence behind the second stronger wave Sunday afternoon and
evening. Will take a peak at some of the 18Z HiRes models and then
make a final decision to upgrade or cancel and if the times need
to be refined.

&&

.SHORT TERM...(Today and tonight)
Issued at 452 AM MST Sat Dec 2 2023

No changes to the big picture, but models and our forecasts
continue to struggle a bit with the timing of the weather
associated with fast moving shortwaves. One area of lift will move
from the mountains across the plains this morning with a quick
shot of enhanced snow showers for the mountains and clouds for the
plains for a few hours. Then there`s a break this afternoon, and
warm advection clouds ahead of the next wave will be moving in
this evening.

Winds aloft will start to increase, but we won`t have a favorable
temperature/shear profile for wave amplification, just very
strong flow over the ridge. For tonight, the high wind threat is
probably mainly above 8,000 feet due to the momentum spilling
over, but it will be hard to get it to descend. There will be a
better chance of wave amplification and more widespread high winds
later on Sunday.

As for the snow, after this little batch the next several hours it
will probably be light for much of the day. With cold
temperatures, there will likely still be some impact, but the more
heavily maintained mountain highways should see some improvement.
Stronger flow aloft and increasing lift will produce heavier snow
tonight, especially near the northern border.

We changed the timing on the High Wind Watch to start at 8 PM. No
other changes to the highlights.

.LONG TERM...(Sunday through Friday)
Issued at 452 AM MST Sat Dec 2 2023

By Sunday at 12Z, an upper trough is exiting the CWA with strong
north-northwesterly flow aloft behind it through the day and
Sunday night. There is a jet maximum over the CWA Sunday afternoon
with speeds in the core of 110-125 knots depending on the model.
There is fairly strong upward vertical velocity Sunday morning on
the QG fields. The orographic snowfall in the mountains looks
pretty decent Sunday morning with deep moisture on the cross
sections. The moisture decreases gradually Sunday afternoon and
Sunday overnight, but will still need substantial pops for the
high mountains through Sunday night. Some of the models even have
some moisture over the western half of the plains on Sunday, but
the strong downsloping will keep pops very low. The strong
downsloping over the foothills will keep snow highlights away from
those areas as well. Will keep snow highlights going in the
mountains and high Parks. With various model inputs as well as the
orographic snow model, will increase the snowfall amounts for
Zones 31, 33 and 34, and will get those numbers in the highlight
statement.

Concerning the high winds, I will extend the High Wind Watch for the
rest of Sunday (afternoon) and Sunday evening based on the very
strong winds aloft and cross sections showing a mountain wave set up
late afternoon into the Sunday evening.

On Monday and Monday night, the flow aloft becomes more
northwesterly and decreases gradually. Shallow moisture is progged
to linger in the high mountains early Monday, but the airmass is
pretty dry both periods. For temperatures, Sunday`s readings will
stay below normal values, with a decent warm-up, especially on the
plains, for Monday.

For the later days, Tuesday through Friday, upper ridging and a dry
airmass moves into and across the CWA Tuesday through Wednesday
night. Zonal flow aloft will increase Thursday into Friday,
becoming more southwesterly Friday night in advance of an upper
trough for next weekend. Moisture will also increase Friday and
Friday night with the incoming system. Temperatures will stay
above normals Tuesday through Friday, with Wednesday being the
warmest day.|

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1125 AM MST Sat Dec 2 2023

VFR conditions expected this afternoon and tonight. Enhanced NW
winds at 10-20 kts continue through the afternoon with gusts 20-30
kts. BJC will gust higher up to 40 kts. Winds at DEN and APA
decrease early this evening transitioning to southerly by 02z.
Winds increase after 06z out of the SW at 10-15 kts at DEN/APA.
BJC will likely tap more into the enhanced winds off the foothills
early Sunday morning with gusts 35-45 kts with the highest gusts
likely in the 06-12z timeframe.

Winds at DEN/APA will be a challenge Sunday. Winds could stay more
westerly late morning then transition to NW in the afternoon or
they could transition more quickly mid-morning. What we do know is
that winds should settle NW/NNW in the afternoon with gusts. There
is a low chance for gusts above 25 kts. Another element worth
mentioning will be the low chance ( < 20%) for a brief snow shower
in the morning (13-17z) timeframe. Communicated this potential as
a VCSH shower for now due to the low probability. If these showers
occur, brief reduction in visibility and lower ceilings (MVFR)
could be possible.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 8 PM this evening to 11 PM MST
Sunday for COZ030-032.

Winter Storm Warning until 11 PM MST Sunday for COZ031.

Winter Weather Advisory until 8 PM MST this evening for COZ033-
034.

Winter Storm Warning from 8 PM this evening to 11 PM MST Sunday
for COZ033-034.

High Wind Watch from 8 PM MST this evening through Sunday
evening for COZ035-036.

&&

$$

UPDATE...Meier
SHORT TERM...Gimmestad
LONG TERM...RJK
AVIATION...Mensch