529
FXUS65 KBOU 220529
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1029 PM MST Tue Jan 21 2025

.KEY MESSAGES...

- Windy with areas of blowing snow tonight in the Front Range
  mountains, foothills and immediate plains.

- Light mountain snow will return Wednesday by sunrise.

- Temperatures moderating somewhat through the rest of the week,
  with Friday seeing near normal to slightly above normal temps.

- Another system expected late Friday into Saturday, with
  increasing potential for moderate snow for the mountains,
  foothills and urban corridor.

&&

.UPDATE...
Issued at 940 PM MST Tue Jan 21 2025

Cameras and observations are showing decent winds with blowing
snow across the foothills and immediate plains. Some areas have
visibilities down below 1/4 mile with the blowing snow. Wind
speeds are as high 50 mph in parts of Zones 35, 36 and 39 with
some likely higher in the normal windiest places. As a result,
will keep the High Wind Warning going until 06Z. Satellite
pictures and cross sections indicated that skies will be mostly
clear to partly cloudy early tonight with increasing cloudiness
after midnight in the alpine areas. Will keep the 10-40%s pops
going in the high mountains by 12Z, and they still look to
increase Wednesday morning for light snow likely.

Current temperatures are in the 20s to lower 30s F over most of the
plains. There are a few readings right around zero F currently,
mainly in Middle Park. Current going overnight low temperatures
look reasonable with only some minor adjustments needed.

&&

.SHORT TERM /Through Wednesday/...
Issued at 106 PM MST Tue Jan 21 2025

Well folks we did it, we finally reached close to, if not several
degrees above, freezing in many spots this afternoon, minus the
mountain valleys and the high country itself. Those southwest winds
really helped to scour out the low-level arctic airmass over the
foothills, urban corridor, and the plains. The airmass that only
penguins and polar bears enjoy - I assume.

Winds over the next 24 hours will become quite or continued strong
(high country) as the next clipper like system dives through the
region on Wednesday. There is a hint of mountain wave developing,
continuing to strengthen late tonight, but as mentioned before we
have some meager height falls and don`t see a ton of capping aloft
(WAA) and the cross barrier flow isn`t 100% west-east either.
Regardless there is enough of all of the above to allow some better
mixing and wave breaking farther east into the urban corridor late
this evening through much of the overnight hours. Gusts could reach
up to 30-40 MPH across the urban corridor and plains, nearly 80-90%
chances, and then pushing 60-65 MPH over the high country and
adjacent foothills, 80-90% as well. The mountain wave is expected to
pull farther west again by mid-Wednesday morning as the
aforementioned clipper/shortwave moves through with the second
momentum transfer/gusts to the region. Fortunately the winds will
help keep us from decoupling too much tonight allowing overnight
lows to only drop into the teens across the plains and urban areas,
and single digits in the foothills...much colder over the mountain
valleys where mixing is harder to come by.

Not a lot of moisture with the quick moving system and again the
cross barrier flow isn`t 100% great for upslope either, so expecting
just a handful of inches of fresh powder for the northern mountains.
Temperatures are expected to climb back towards the freezing mark
but not too much higher than low-30s in the wake of the shortwave.

&&

.LONG TERM /Wednesday night through Tuesday/...
Issued at 106 PM MST Tue Jan 21 2025

A secondary weak shortwave clips Colorado Wednesday night into
Thursday, with the mountains continuing to squeeze out some light
snow showers through Thursday morning, although amounts should be
fairly inconsequential. This wave will pump the brakes on the
warming trend, with snow cover and clouds keeping things cooler in
the morning, and strengthening north winds behind the shortwave
having the same effect in the afternoon for the plains. Highs will
therefore hover within a few degrees of the freezing mark for the
lower elevations, with temperatures also holding steady in the
high country. There could be pockets of patchy blowing (or more
likely drifting) snow Thursday afternoon in the plains as gusts
push above 30-35 mph, although generally the stronger winds should
be in areas of limited to no snow pack.

Upper-level ridging replaces the outgoing shortwave as we head
into Friday, finally allowing for a more noticeable warm up into
the upper 30`s and potential 40`s east of the mountains. That
said, there`s still room for temperatures to end up on the lower
end of guidance if we see an earlier frontal passage.

On the topic of the frontal passage... we`re still seeing
relatively ample run-to-run consistency pointing to a rapidly
amplifying positively-tilted trough along the West Coast later on
Friday (Canadian ensemble suite aside), and favoring the
development of a surface low to the S/SE of our forecast area
around Friday night, which should bring an 80% or higher chance of
snow to much of the region. As is typical, the mountains should
be first in line, with snow potential ramping up starting Friday
afternoon as flow aloft becomes more zonal and moisture advection
increases. Conditions will gradually become more favorable for
snow to spread into lower elevations Friday evening and especially
overnight as low-level flow takes on a more northeasterly
component behind the front and moisture deepens. Forecast
soundings indicate potential for a brief period of heavier snow
with a well-saturated DGZ Friday night or Saturday, and possibly
some contribution from the right-entrance region of a modest jet
streak. Upslope flow looks to be mostly on the shallow and weak
side, but nonetheless should be present in some capacity. There
are still notable differences in moisture content and track which
make it too early to discuss accumulation details, but a light to
moderate snowfall event looks increasingly likely (80% chance)
for the urban corridor and foothills, with moderate snow
anticipated in the high country, particularly the northern
mountains.

There`s a little less certainty as far as how quickly this system
will move out, with the Canadian ensemble suite especially excited
about Sunday precipitation potential. For now, will retain a
chance (25-40%) of snow for the lower elevations Sunday, with
greater potential for snow to linger the high country. Regardless,
colder temperatures will unsurprisingly be making a return for the
weekend as highs drop back into the 20`s.

Solutions start to diverge more considerably come early next week,
though generally favor a drying trend into at least Monday with
some moderation in temperatures.

&&

.AVIATION /06Z TAFS through 06Z Thursday/...
Issued at 1029 PM MST Tue Jan 21 2025

Gusty west to northwest winds will continue to be the main
weather focus over the next 24 hours. West-northwest winds to 30
knots at DEN will continue through the next 2-3 hours. Winds then
slowly begin to decrease. This will be temporary as gusty
northwest winds develop again late Wednesday morning 17-18Z. The
strongest winds will be the next 2-3 hours at BJC with gusts to 45
knots. No ceiling or visibility issues are expected, though
blowing snow could make runways slick.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 11 PM MST this evening for COZ039.

&&

$$

UPDATE.......rjk
SHORT TERM...Heavener
LONG TERM....Rodriguez
AVIATION...Meier