524
FXUS65 KBOU 212344
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
444 PM MST Sun Dec 21 2025

.KEY MESSAGES...

- Elevated to critical fire conditions across portions of the
  foothills and South Park on Monday as winds increase in the
  higher terrain.

- Record warmth likely across most of the I-25 corridor and
  plains Monday, with highs in the upper 60s to mid 70s.

- Warm and dry through Wednesday, and Christmas still warm for
  the plains. Some hints of a more wintry pattern in the mountains
  in the latter half of the week?

&&

.DISCUSSION /Through Sunday/...
Issued at 327 PM MST Sun Dec 21 2025

Fairly impressive temperature gradient across the I-25 corridor
this afternoon, with the southeast side of the Denver metro
sitting in the upper 60s (and a 70F at CFO), while 50s are a much
more common number off to the north. If the current temperature at
DEN holds at 67F we`d tie another daily record high.

Main story for the start of the week will be the near-record to
record high temperatures across most of our lower elevations.
Ridging is starting to slowly build across the southern CONUS, but
there`s still just enough flow aloft (generally 50-70kt at/above
ridgetop) for some gusty winds to develop. Guidance tries to
briefly bend that back down into the lower foothills. The
combination of guidance that worked well with the last couple wave
events (HRRR/RRFS/RGEM) all bring gusty winds down to the base of
the foothills. Combined with the record warmth and drying airmass,
we could see some elevated to critical fire weather conditions.
More on that in the Fire Wx section. There`s much less confidence
that any gusts will make it into the lower elevations, but warming
mid-level temperatures and the increased downslope component
should allow temps to reach the mid 70s in some places. Tomorrow`s
record high at DEN (70F) is likely to be broken, and other places
in the eastern plains may shatter their daily records by several
degrees.

For Monday night through Wednesday, upper level ridging will be
well established over the south central and southeast part of the
country with a mild and dry southwest flow aloft over Colorado.
For Thursday, southwest flow aloft increases as the upper level
ridge is nudged eastward by a large upper level trough off the
west coast of North America. For Tuesday, Wednesday (Christmas
Eve), and Thursday (Christmas Day), temperatures will continue to
be well above average with highs in the mid 60s to lower 70s
across northeast Colorado. Periods of high clouds are expected, so
if we end up seeing a day where high clouds persist for most/all
day, we could fall short of the mid 60s. Winds don`t look to be an
issue especially Tuesday and Wednesday under weak flow aloft. As
flow aloft increases on Thursday, gustier winds will be possible
for the mountains and foothills, but less than we saw this past
week. The increasing southwest flow aloft will transport Pacific
moisture into the area Thursday (Christmas Day) bringing snow to
the mountains. Southwest flow aloft tends to bring better/heavier
snow to the western mountains versus the central mountains.

For Friday and next weekend, an upper level trough dives
southeast along the west coast closing off over central to
southern California. This helps create a split low aloft across
western North America. Over Colorado on Friday, we`ll see
southwest flow aloft continue with a chance for snow (possibly a
little valley rain) in the mountains. High temperatures begin to
cool slightly but stay well above normal with highs in the upper
50s to mid 60s. For the weekend, there`s some uncertainty where
the cutoff low over the southwest part of the country will be.
Likely too far southwest of Colorado to bring much precipitation
east of the mountains. However, the mountains mainly see snow,
heaviest in the southwest mountains. A trough in the northern
branch passes well north of Colorado, but a weak cold front slides
southward bringing cooler, near normal temperatures for the
weekend. Even though there`s a good amount of uncertainty on the
placement of the closed low, models have been in good agreement
with this cool down for the weekend.

&&

.AVIATION /00Z TAFS through 00Z Tuesday/...
Issued at 444 PM MST Sun Dec 21 2025

VFR will persist through the period with only SCT-BKN high clouds.
Winds will transition to normal SSW at 9-14 kts through 02Z and
then hold through at least 16Z Monday. There is just a slight
(20%) chance of a disruption to VRB winds during that period. By
18Z-20Z, more mixing will occur and slight mountain wave
enhancement is possible, just enough to bring a relatively high
(60-70%) chance of gusty west winds into the airports, likely
first starting at KBJC and working east to KDEN toward 19Z-21Z. A
few brief gusts to 25-30 kts not impossible, but most likely gusts
closer to 18-22 kts when/if the winds increase. A 30-40% chance
the winds just go VRB after 18Z Monday.

&&

.FIRE WEATHER...
Issued at 241 PM MST Sun Dec 21 2025

Another day of elevated to critical fire weather conditions is
likely on Monday as another (weaker) mountain wave event sets up
later tonight into Monday. The overall mountain wave setup isn`t
particularly impressive, but there`s enough flow at ridgetop and
hints of a stable layer that we have reasonable confidence in a
few 50-65 mph gusts developing across the Foothills. Well above
normal temperatures and dry conditions (RH as low as 10%) will be
common across a lot of the foothills and I-25 corridor. Although
some portions of the northern Foothills (Red Feather Lakes, for
example) did see some snowfall this weekend, the majority of fire
zones 214/215/216 did not... so we assume that all of these
locations would have receptive fuels. The one lingering question
right now is how much overlap we`ll see between the gusty winds
(more likely in the mid/higher foothills) and the critical RH
values (more likely for the mid/lower foothills). There`s enough
confidence in some critical fire weather conditions for a Fire
Weather Watch, and we`ll let the evening/overnight shift evaluate
the wind forecast as new guidance comes in.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Monday morning through Monday afternoon
for COZ214>216.

&&

$$

DISCUSSION...Hiris/12
AVIATION...20
FIRE WEATHER...Hiris