851
FXUS65 KBOU 161752
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1052 AM MST Tue Dec 16 2025

.KEY MESSAGES...

- Strong downslope winds to impact the mountains, foothills, and
  I-25 corridor Wednesday afternoon into Wednesday night, with
  potential for widespread gusts 60-85 mph, strongest near the
  base of the foothills. Breezy conditions will extend into the
  plains through Thursday morning.

- Critical fire weather conditions can be expected Wednesday
  afternoon for the urban corridor.

- Mountains to see deteriorated travel conditions Wednesday
  evening/night due to banded snowfall and wind.

- Another round of gusty winds and high fire danger looks likely
  (75% chance) on Friday.

&&

.UPDATE...
Issued at 207 AM MST Tue Dec 16 2025

Confidence has increased sufficiently to allow for some headline
changes and upgrades. Here is a rapid fire summary of those
changes:

- The mountains, foothills and urban corridor have been upgraded
  to a High Wind Warning, with peak gusts 60-85 mph anticipated.
  The High Wind Warning for the mountain zones was extended
  through early Thursday morning.

- A High Wind Watch has been issued for our northern plains
  (Weld, Morgan, and Logan Counties) for Wednesday evening, given
  potential for Bora-driven gusts reaching 60 mph.

- The Fire Weather Watch for the urban corridor has been upgraded
  to a Red Flag Warning for Wednesday, and expanded to include the
  Palmer Divide.

With the headline changes covered, queue a succinct outline
("succinct" is questionable) of a few focus areas:

Forecast soundings and cross-sections are still reticent when it
comes to developing a notable critical layer Wednesday, and are
even suboptimal as far as inversion positioning aloft is
concerned. However, shear profiles become favorable for wave
propagation near midday with between 15 and 30 kts of weakening
through ~450-500mb, also coincident with the arrival of hefty
subsidence preceding the jet max and front. These factors should
allow for a somewhat short-lived window of robust mountain wave
enhancement, which we are seeing highlighted by hi-res guidance
now that we`ve entered the 48-hr window. Specifically, there`s a
fairly consistent signal for a surge of 60-80 mph gusts into the
western urban corridor during the afternoon, lasting ~3-4 hours.
Although these details could still change some, it was hard to
justify not proceeding with an upgrade to High Wind and Red Flag
Warnings.

Additionally, the strong subsident flow accompanying the
transition to Bora-driven winds Wednesday evening could support
gusts near 60 mph over our northern plains, hence their inclusion
in a High Wind Watch, although confidence in this potential is
still fairly limited (around 50%).

Finally, contemplated (but didn`t proceed with) a Winter Weather
Advisory for our northern mountains for late Wednesday. Model
consistency isn`t all that great, with a still substantial QPF
spread and some questionable moisture profiles. The one wildcard
is the potential for heavier banded snowfall, fueled by strong
ascent beneath the approaching left exit region of the jet and
ample frontogenesis. Gusty winds would further add to the possible
deterioration in travel conditions. Ultimately though, there`s
still time to iron out these nuances and tilt the balance in
either direction, so will punt this target of opportunity to
subsequent shifts. On a side note, PoPs were increased slightly
for the urban corridor after 6pm Wednesday, when some light rain
and rain/snow showers will be possible (40-60% chance).

&&

.SHORT TERM /Through Monday/...
Issued at 302 PM MST Mon Dec 15 2025

Current satellite imagery shows mostly clear skies across the
forecast area. Temperatures are about 15 to 20+ degrees above normal
on the plains, ranging between low and high 60s, with a few stations
in the southern Denver metro reaching low 70s. We have officially
tied our record high temperature for DIA (68 set in 1921), and won`t
be surprised if we are able to warm up another degree or two to
break the record. Other than that, quiet conditions prevail for the
mountains and plains this evening and tonight.

It will be warm and mostly dry on Tuesday as upper level flow
flattens due to a shortwave trekking south of Colorado. With
increased flow aloft, expect breezy conditions along the high
terrain and areas off the Cheyenne Ridge. Cross-sections do indicate
moisture embedded in the flow, so can`t rule out a snow shower in
the northern mountains and an isolated light rain shower or two in
the northern plains and foothills, particularly in the morning.
For the rest of the day, downsloping winds will create elevated
fire weather conditions (see Fire Weather Discussion below) and
allow temperatures to rise into the mid-to-high 60s again. While
unlikely, we do have the potential to break the max temperature
(70 degrees set in 1980).

&&

.LONG TERM /Tuesday night through Monday/...
Issued at 302 PM MST Mon Dec 15 2025

Strong winds will return to the mountains and potentially the
I-25 corridor on Wednesday. The mid and upper level flow will
increase along the Front Range Wednesday morning and into the
afternoon. Winds are forecast to peak Wednesday afternoon and
evening with cross barrier flow around 60 to 70kts at mountain
top. Wind gusts in the higher elevations could approach 90 mph at
times Wednesday afternoon. The soundings from the global models
are missing a critical layer and the inversion above ridge top is
not at the ideal level for a downsloping event, both of which will
hinder the winds ability to push eastward into the lower
foothills and surrounding plains. However, some of the higher res
models, like the RRFS, are starting to show both a critical layer
and inversion, which helps increase our confidence that stronger
winds could move further east into the I-25 corridor Wednesday
afternoon. Also, a few ensemble members of both the GEFS and
European are showing gusts in the 60 to 75mph range in the
foothills and at the base of the foothills. We`ll get a better
idea on the potential for the winds to push further east as the
high res models continue to come in and we`ll continue to keep an
eye on the potential for a critical layer and inversion.

Another thing to watch for Wednesday is the cold front moving in
from the northwest Wednesday evening and overnight. Just ahead of
the front, we could see mountain wave enhancement, which would help
give the winds the extra push they need to reach Boulder and west
metro Denver. As the front moves in, the winds will turn from a
chinook event into more of a bora event, with decent northwest winds
behind the front. Right now, winds behind the front look to stay
around 20 to 30mph with gusts around 40mph. However, the GFS does
keep winds a bit higher behind the front, with some sustained speeds
closer to 40mph. Temperatures will be cooler and much closer to
normal for Thursday afternoon thanks to the front.  RH is expected
to drop to 15-20% across the I-25 corridor.  With the potential for
high winds several hours Wednesday afternoon, there are significant
fire weather concerns covered in in the fire weather discussion
below.

Winds will pick back up Thursday night into Friday. Wind gusts at
higher elevations could be in the 70 to 90mph range again Friday
morning. Once again, we have lower certainty in how far east the
stronger winds will push. Right now, we`re keeping the stronger wind
gusts (50+mph) generally above 7000ft. With the downsloping winds
again on Friday, temperatures will warm back up to potentially
record breaking highs. Weaker downsloping winds and the approach of
a low pressure system and cold front will keep temperatures a few
degrees cooler for the weekend, but highs will remain well above
normal.

Now onto precip chances. The mountains will have a few chances at
snow this week. The first round will be associated with the strong
west upslope flow, decent moisture, and frontal passage Wednesday
into Thursday. The higher elevations of the Front Range and Park
Range could see a around 2 to 6 inches of snow, with some higher
amounts on the peaks. The foothills and plains also have a chance of
precip with the frontal passage, but chances will be low (35kt gusts for most of the afternoon into
the evening, but also low confidence on the timing/duration of
stronger winds.

Meanwhile, BJC continues to bounce in and out of the stronger
westerly gusts today. Most guidance eventually retreats these
gustier winds back towards the foothills later this afternoon,
but some sort of west wind is likely to continue this evening into
tonight. Much higher confidence of gusty winds developing at BJC
near/after 18z tomorrow.

&&

.FIRE WEATHER...
Issued at 207 AM MST Tue Dec 16 2025

Near-critical fire weather conditions will persist through the day
today across the lower foothills and Cheyenne Ridge, where
humidity will hover in the mid-teens to around 20% with gusts
25-40 mph.

On Wednesday, downslope winds will increase through the day and
become strong by the afternoon, when they`re expected to spread
east of the foothills into the western urban corridor with gusts
55-85 mph (strongest expected in the vicinity of the Rocky Flats).
This surge should be somewhat short-lived (a few hours), with the
stronger winds retreating into the higher terrain in the evening.
However, they`ll be coincident with relatively low humidity values
in the 18-28% range, and thus supportive of rapid fire spread.
These critical conditions will extend along the majority of the
I-25 corridor, from the WY state line south through the Denver
metro and into the Palmer Divide.

There may be a few pockets of elevated fire weather conditions in
the plains Thursday with lingering breezy northwest winds and
15-20% afternoon humidity, but Red Flag conditions appear unlikely
at this time (20% chance).

Friday still carries higher potential for the return of critical
fire weather conditions, with guidance favoring another round of
downslope winds, combined with expected warm and dry conditions.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 11 AM Wednesday to 5 AM MST Thursday for
COZ033-034.

High Wind Warning from 11 AM Wednesday to midnight MST Wednesday
night for COZ035-036-038-039.

Red Flag Warning from 11 AM to 6 PM MST Wednesday for COZ238>243-
245.

High Wind Watch from Wednesday afternoon through Wednesday
evening for COZ042-044-048.

&&

$$

UPDATE...BRQ
SHORT TERM.....12
LONG TERM...AP
AVIATION...Hiris
FIRE WEATHER...BRQ

NWS BOU Office Area Forecast Discussion