638
FXUS65 KBOU 121134
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
434 AM MST Wed Feb 12 2025

.KEY MESSAGES...

- Arctic cold through Thursday morning. Highs only around 10F
  today. Lows below zero in almost all areas tonight and in some
  cases, well below zero!

- Snow event ending on the lowest end of guidance for many
  locations. Just lingering light snow/flurries this morning, and
  a few showers in/near the higher terrain this afternoon.

- Prolonged mountain snow Thursday night through Saturday, with
  moderate to heavy accumulations and expected travel impacts.

- Warmer/drier Thursday-Friday for lower elevations, then snow
  returning Friday night/Saturday.

- Active pattern continues into next week, with increasing
  potential for another system Monday into Tuesday.

&&

.SHORT TERM /Through Tonight/...
Issued at 230 AM MST Wed Feb 12 2025

The last wave of appreciable snow (and there wasn`t a whole lot of
that for Denver) is moving off to the east early this morning.
The old adage of "too cold to snow" comes to mind, so there could
have been a little of this aspect in the low specific humidity
airmass, but also winds never really turned upslope so that
component considerably underperformed. Also, Denver got the split
of any banded snow, but a few locations outside of Denver where
the bands occurred got 3+ inches.

Only now are we trying to turn winds slightly upslope to 010
degrees - a little late and behind all the synoptic support. Thus,
only light snow or flurries will be left behind, but enough
lingering travel impacts to marginally keep the Winter Weather
Advisory in place. We think that will be toast (had to think of
something warm) by the end of the commute or 9 am. Some flurries
could still linger in the arctic cold into mid day, while also
some sunshine starts to break through. Despite the sun, there`s
another weak surge noted pushing into northeast Colorado this
morning essentially keeping the arctic air anchored in place.
Thus, we don`t think much warming will occur, although some
partial breaks in the clouds should allow locations to push out of
the single digits. Some guidance, however, keeps us just below
10F, so a 30% chance we don`t reach 10F. Mountain snow showers
should continue into afternoon, but will be light. A few of these
could drift onto the adjacent plains, but not much more than
flurries or a brief period of light snow expected.

For tonight, skies will gradually clear this evening as drier air
moves in. Winds will be light, but it won`t take much with
plunging temperatures to create dangerously cold wind chills. It
looks like most of the plains and foothills (outside of the
immediate Denver metro area/downtown) will see wind chills of -15F
or colder, or just plain old air temperatures down to -15F in the
coldest/calm spots. Thus, we`ve issued a Cold Weather Advisory
for all of the foothills, I-25 Corridor, and plains. This does
include Denver (colder wind chills eastern half of metro) where
light drainage winds will set up. That will also help alleviate
lows from plunging in Denver, where we typically see an evening
low and then slowly rising temperatures overnight. The same should
play out tonight. Meanwhile, temperatures in valley locations
won`t bottom out until early Thursday morning.

&&

.LONG TERM /Thursday through Tuesday/...
Issued at 149 AM MST Wed Feb 12 2025

Despite a bitterly cold start to the morning on Thursday,
temperatures will be quick to rebound once we mix out, climbing into
the upper 20`s to mid 30`s for the lower elevations and high valleys
as we return to a subsident regime and clouds clear. Save for a
chance of some light snow showers late evening for our westernmost
mountains, it will be the one day in the forecast period absent
of notable precipitation chances for pretty much all areas.

Thursday night into Friday, zonal flow aloft will give way to
strengthening southwest flow as a trough deepens over the West
Coast, helping advect a healthy plume of Pacific moisture into the
region, particularly for the high country. Thus, the mountains
are in store for another round of impactful snow accumulations
that will be focused during the daytime hours on Friday. Headlines
will be needed for this event for the higher mountain zones, but
will wait until our current highlights run their course before
issuing anything. Meanwhile, downslope flow will keep the lower
elevations considerably warmer and likely dry through the
afternoon, with a 65% chance of highs exceeding 50 degrees for the
Denver metro. Come Friday evening, the associated cold front will
descend through the plains and bring much greater potential for
precipitation to the lower elevations through the overnight
period. Mid-level lapse rates look to be quite healthy at between
8-9C/Km which could support some convective-type elements, and we
should see at least a short period of weak east/northeast upslope
flow post frontal passage, leading to fairly high confidence in
another round of snow. Higher amounts should favor those locations
closer to the foothills and the southwestern Denver metro into
the Palmer Divide, although ensembles are still latching on to a
notable spread in QPF with this event. In all, favoring light to
moderate accumulations for the lower elevations, with a relatively
prolonged moderate to heavy snow event for the mountains
(including into Saturday, see below).

Activity is then slated to dwindle slightly Saturday morning before
we see a switch to northwest flow aloft later in the day as a NW-SE
oriented jet traverses overhead. This will favor another wave of
more widespread snow in our mountains, with potential for some
light spillover into the lower elevations.

Some reduction in moisture availability and the strength of
northwest flow is progged for Saturday night into Sunday,
confining snow chances to the higher mountain elevations where
the orographic component still seems sufficient enough to sustain
some light snow. Otherwise, most areas should be a little milder
and stay dry.

Looking ahead at next week, the pattern will remain conducive for
additional storm systems to impact the state. Ensemble suites
unsurprisingly continue to wobble in their solutions, but
generally favor deepening upper-level troughing late Monday into
Tuesday for the return of widespread winter weather potential to
the entire region. Higher confidence in impacts for the mountains
at this stage, but an impactful storm for the lower elevations is
still in the mix of possible scenarios.

&&

.AVIATION /12Z TAFS through 12Z Thursday/...
Issued at 434 AM MST Wed Feb 12 2025

MVFR or at a minimum IMC will prevail through 18Z, with off/on
light snow or flurries. Visibilities should mostly range 3-6SM
in the light snow, with ceilings anywhere from 2000-4000 ft AGL
for the Denver area TAF sites.  Still can`t rule out some
flurries beyond 18Z with a weak upslope (north/northeast wind)
lingering, but chances mostly push to in/near the foothills and
away from KDEN. Any ceilings will then be breaking up 00Z-03Z as a
downslope component and light drainage develops. No threat of fog
tonight with the light downslope winds.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 11 AM MST this morning for
COZ033>036-038>051.

Cold Weather Advisory from 8 PM this evening to 8 AM MST
Thursday for COZ035-036-038>051.

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Rodriguez
AVIATION...Barjenbruch