739
FXUS65 KBOU 181128
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
428 AM MST Thu Dec 18 2025

.KEY MESSAGES...

- Strong winds and critical fire weather conditions continue
  through early this afternoon for the northeast plains.

- Strong downslope winds return Friday to our mountains, foothills
  and parts of the urban corridor, with widespread critical fire
  weather conditions anticipated under a dry and (record) warm air
  mass.

- Light to moderate snow returns to the mountains Saturday, with
  deteriorated road conditions expected.

- Drier and more seasonal conditions expected Sunday onwards, with
  generally weaker winds.

&&

.UPDATE...
Issued at 317 AM MST Thu Dec 18 2025

Some quick-hitting updates from the night shift...

Winds have come down compared to daytime magnitudes, but even
still are gusting 45-50 mph across much of our northern plains,
and the higher mountains may continue to see gusts to 75 mph
through this morning, where the High Wind Warning was extended.

The forecast hasn`t changed much for today, with the focus of
impacts being in our northeast plains as strong northwest winds
mix down to produce gusts 45-65 mph through about midday,
strongest in Sedgwick/Phillips Counties. Opted to issue a Red Flag
Warning for the windier locations despite projected diurnal
humidity values of 15-25%. The wind`s ability to spread fire in
our plains despite marginal humidity conditions was aptly
demonstrated over the past few hours in Yuma County, and
conditions today won`t be much different.

Regarding Friday...there`s going to be a strong mountain wave,
little doubt about that. Where questions remain (as usual) is in
the eastward spread of strong wind gusts > 75 mph into adjacent
lower elevations Friday afternoon. CAMs still disagree
particularly on the vertical placement of a stable layer (though
unanimously depict one), but there`s enough cause for concern,
especially with optimal wind directions above ridgetops and jet-
induced subsidence. The HRRR is particularly bullish with both
speeds and spatial extent. In any case, Friday`s air mass looks
impressively warm and dry, such that humidities in the teens could
not only be quite durable (potentially lasting well into the
evening), but also extend into much of our foothills. This will be
a high-end Red Flag day for many locations given the above, with
just a little uncertainty as to just how widespread winds will be
over the lower elevations. The Fire Weather Watch was thus
expanded to include all of our foothills, I-25 corridor, and some
of our plains, and extended through Friday night.

UPDATE Issued at 844 PM MST Wed Dec 17 2025

Made a few changes this evening with stronger winds over the
plains, resulting in areas of blowing dust and hazardous travel
conditions. We earlier extended the High Wind Warning for the
Fort Collins to Wyoming border area til midnight to account for
the northwest winds blasting across the border, while also adding
Limon to the High Wind warning as shower enhancement was aiding
frontal winds. There have been a few impressive gusts over 70 mph
on the northeast plains this evening!

Winds had settled down (but still gusty) close to the foothills,
so the High Wind warning for Boulder was allowed to expire at 7
pm. Meanwhile, with the mid/upper level jet core ripping across
the mountains we`ve seen a few of the passes and higher mountains
blast to over 100 mph. Those types of winds will likely remain
overnight with the core of 600 mb winds near 80 kts holding in
place. So any sort of amplification will bring higher winds.
Higher foothills will also see a few blasts of these magnitudes
given developing mountain top stable layer overnight. Also, a few
light showers spreading onto the plains this evening but those and
the mountain snow/blowing snow will be diminishing rather quickly
by midnight as much drier air arrives.

&&

.DISCUSSION /Through Wednesday/...
Issued at 350 PM MST Wed Dec 17 2025

Winds are currently peaking across the Front Range and lower
foothills, with multiple reports of 80+ mph wind gusts. Hi-res
guidance continues to indicate strong winds continuing for the
next couple of hours for the lower elevations before backing up
into the mountains again this evening. We are still on track to
let the High Wind Warning expire for the lower foothills this
evening, and let the High Wind Warning for the mountains to
continue through tomorrow morning. While there will be brief lulls
in strong winds along the mountains overnight, generally expect
gusts up to 80 mph at times, with a gradual weakening through
Thursday late morning/early afternoon.

For the plains, gusty winds will continue through early this evening.
Then, a cold front is progged to enter the northern plains by 6/7
PM and quickly sweep south. QG fields show deep subsidence over
the plains, which will likely help bring down strong winds to the
surface. Gusts up to 60 mph are possible, particularly off the
Cheyenne Ridge. However, short-range guidance has continued to
indicate the strong winds reaching all the way down to Washington
county, so have included them in the warning. After midnight,
northwest winds weaken below high wind criteria. However, expect
gusty winds up to 40-50 mph to continue through the morning hours
Thursday.

Critical fire weather concerns are expected to continue this
afternoon despite marginal relative humidity values. Strong winds
along the foothills and adjacent plains will promote rapid fire
spread, should a fire occur. However, as winds weaken this evening
along the foothills, conditions will improve to let the Red Flag
Warning expire. In addition, even with the strong winds expected
with the cold front, slightly higher relative humidity values and
cooler temperatures will keep fire weather concerns at bay.

The Winter Weather Advisory will continue through tonight. Current
radar imagery shows snow showers ongoing for the northern mountains,
with minimal accumulations so far. However, with guidance indicating
strengthening frontogenesis across the higher terrain, banded snow
is possible, with snowfall rates reaching 1"/hr to briefly 2"/hr.
Total snow accumulations of 3-8" is still on track, with localized
higher amounts of 10" possible near ridgetops. Strong winds will
cause blowing snow along high passes, which will greatly reduce
visiblities.

Now for tomorrow. In general, cool temperatures and gusty winds are
expected for the entire forecast area. However, the primary
concern for strong winds will be across the northeastern plains in
the morning. The core of the upper level jet streak is still
progged to be overhead Thursday morning, with the 700-mb flow
reaching up to 70-80 kts. Modeled soundings indicate steep lapse
rates at the same time, which will help mix strong winds down to
the surface. In addition, hi-res guidance has continued to show
gusts reaching, or barely exceeding, high wind criteria. For this
reason, have opted to upgrade Sedgwick and Phillips counties to a
High Wind Warning tomorrow, with gusts up to 55-65 mph possible.
Elevated to critical fire weather conditions are possible,
particularly over the eastern plains (see Fire Weather
Discussion).

Another mountain wave and high wind event is expected along the
front range and foothills late Thursday into Friday. Models are
showing cross barrier flow around 70 to 100kts at ridge top. There
is a robust pressure gradient shown in the Sangster, with MSL
differences around 13 to 14mb between GJT and DEN. Models are
hinting at a weak inversion around 600mb in the afternoon and
showing some inverse shear in mid levels (80kts to ~50kts higher
up). The relatively weak nature of these ingredients lower
confidence a bit in the winds making it down towards the I-25
corridor. But, as we saw with the current event, this can definitely
change as we get closer to the event. Right now, we have very high
confidence in strong winds impacting the higher elevations of the
front range, with lowering confidence of really strong winds the
further east we go. A High Wind Watch will be in effect late
Thursday through late Friday for the mountains and Friday afternoon
for zones 38 and 39. The strong winds and dry conditions will lead
to fire weather concerns as well (see Fire Weather Discussion).

Weak QG subsidence Friday afternoon will transition to weak ascent
in the evening as the left exit region of the upper level jet
approaches. The approach of the jet will help bring an end to the
high wind event and trigger some snow showers in the mountains. The
best chance for snow this weekend will be overnight Friday into
early Saturday afternoon, with lower chances (036.

Fire Weather Watch from Friday morning through Friday evening
for COZ215-216-238>243-245>247.

High Wind Watch from Friday morning through Friday afternoon for
COZ038-039.

Red Flag Warning until 5 PM MST this afternoon for COZ242-244-
248>251.

High Wind Warning until noon MST today for COZ050-051.

&&

$$

UPDATE...BRQ
DISCUSSION...MAI/AP
AVIATION...BRQ
FIRE WEATHER...MAI/AP

NWS BOU Office Area Forecast Discussion