Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 092141
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
241 PM MST Fri Dec 9 2022

.SHORT TERM...(This evening through Saturday)
Issued at 241 PM MST Fri Dec 9 2022

Winds are starting to blow over the higher foothills as the
mid level speed max associated with the passing shortwave
approaches. The wave has nosed down into Boulder over the past
hour or so. Speeds are mostly 30-40 mph gusts. We expect the
downslope winds to become more widespread but mainly stay in the
foothills and the spots where it usually leaks out onto the
plains...Rocky Flats/Broomfield, Carter Lake, Cheyenne Ridge.
Speeds will likely come up a bit more but the 50 mph gusts should
be limited to the normally windier areas. There`s still a shallow
moisture layer upstream of the Park Range, but it`s pretty
limited, so the low PoPs we have over the northernmost mountains
through this evening look sufficient.

Skies will clear over the plains pretty quickly, allowing for
another cool night. That upstream cloud layer will be slower to
dissipate, though it should vanish late tonight or Saturday
morning. We`re showing warmer lows around zero in the mountain
valleys based on the clouds, it could drop much colder if they
clear early. A warming and subsident air mass will bring slightly
warmer highs tomorrow. Winds drop off pretty quickly, though there
will still be some over the ridges. Breezy conditions will also
develop over the area south of I-76 in the afternoon, which
combined with low humidities will produce elevated fire danger,
but we`re not expecting Red Flag conditions.

.LONG TERM...(Saturday night through Friday)
Issued at 241 PM MST Fri Dec 9 2022

...Key Messages

1) Large winter storm expected across portions of the region late
Monday through late Tuesday

2) Still ample uncertainty in the track of the developing low
pressure over the plains - track dictates more/less heavier snows
and therefore impacts in tandem with stronger winds

3) Elevated fire danger concerns Sunday across portions of the plains

4) Well below mid-December temperature averages expected through the
week...

Sunday...Short-wave ridging moves overhead and the upper level jet
max pulls farther east across the mid-west allowing surface winds to
relax a bit more. Winds veer more towards the south-southwest on
bumping up daytime temperatures back to 7-10 degrees above climo
averages. With the warmer temperatures and some breezy conditions in
place, elevated fire danger conditions will likely be present across
the Palmer Divide and eastern plains.

Monday...We`ll call this the `Deep Breath Before the Plunge` in a
few ways - big pattern swing, potential high impact winter storm,
and cold temperatures after Monday. Large scale troughing starts to
enter into the Great Basin sending stronger southwest flow aloft
into the region. This will help to keep temperatures above average
for much of the day, drawing up warmer and somewhat moister air from
the south-southeast. The Denver cyclone stands out Monday afternoon
which could help to pull down an encroaching cold front later
Monday...temperatures start to crash behind the front.

Tuesday...The main event. Though modeling has been consistent in the
general placement of the surface low pressure on Tuesday, there are
still small juxtapositions that will greatly affect the overall
impacts from this system. The trends in ensemble guidance have
shifted the position of the surface low a few miles farther north
meaning, winds are a pretty solid lock, and a little bit less snow
outside of the northern mountains and far northeastern plains. We
drop the low`s placement a few more miles south, more snow for a lot
more places. As of now the positive tilt of the mid-level troughing
should transfer the energy from west to east across the state faster
on Tuesday morning meaning a more limited shot of snow across the
Front Range is expected. If we`re able to slow down the troughs
movement a bit more, with stronger downstream blocking, we may be
able to have the trough axis go neutral or negative allowing for a
slightly longer snowfall event overall.

Though details are rather thin at this time we should note that
stronger northerly winds will be in place for much of the day
Tuesday. The colder nature of the system overall could produce snow
ratios into the 12-16:1 ratios, a bit more airy, which would allow
for more blowing of the snow to occur. There is still a lot in play
with both a snow boom or bust that could occur. Ah, forecasting
winter weather with a lee-cyclogenesis in your backyard, it`s rather
"fun" at times.

Wednesday - Friday...Though there may be some lingering wrap around
snow showers on Wednesday as the main trough continues to deepen and
pull away to the east-northeast. A much colder airmass then settles
in place with highs around 5-10 degrees below climo averages and
still rather breezy out east and along the foothills.


&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1124 AM MST Fri Dec 9 2022

VFR through tonight. Typical light winds, except a chance of west
winds gusting up to 30 knots for a few hours at KBJC sometime in
the 03z-09z period.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Gimmestad
LONG TERM...Heavener
AVIATION...Gimmestad


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