276
FXUS65 KBOU 211144
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
444 AM MST Wed Jan 21 2026

.KEY MESSAGES...

- Slightly cooler today, but elevated fire weather conditions
  again across portions of the Front Range and urban corridor.

- Stronger arctic blow now expected Thursday night through
  Saturday night, with delayed moderation Sunday into early next
  week.

- Cold Weather Advisory criteria will likely be met Thursday
  night through Saturday morning over the plains east of I-25
  (>70% chance).

- Areas of light snow Friday - Friday night, possibly lasting into
  Saturday morning.

&&

.UPDATE...
Issued at 251 AM MST Wed Jan 21 2026

Main change is for colder temperature forecasts Thursday night
through Saturday night. While the initial arrival of arctic cold
is still expected Thursday night, there is more agreement now that
additional reinforcement will occur Friday through Friday night,
intensifying the arctic cold. That reinforcement is due to a
trailing shortwave dropping down the backside of the longwave
trough in eastern Canada/Great Lakes region, and carving out
farther to the west than originally forecast. We`ve knocked down
temperatures accordingly, with much higher probabilities (80+%
chance) of Friday`s highs only being in the teens across the I-25
Corridor, and possibly single digits (50-70% chance) on the
eastern plains. Lows Friday night would likely dip to or below
zero with almost certainly below zero readings over the eastern
plains, and then highs on Saturday would struggle again to push
into the teens. With the colder temperatures, there will also be a
stiff easterly wind over most of the plains. Wind chill
temperatures will likely drop to less than -15F in areas east of
I-25, so that would put us in Cold Weather Advisory Criteria from
late Thursday night through most of Friday, Friday night, and
Saturday morning.

While the digging secondary shortwave trough has significant
implications to the degree of cold, it also means increasing
chances of light snow. Initially, the moisture is quite shallow in
the post-frontal upslope regime Thursday night into Friday
morning, so mainly very light snow or flurries expected. However,
there is greater moisture depth associated with persistent lift
and frontogenesis that drops slowly south from the northeast
corner of the state late Thursday night across the rest of the
forecast area Friday through Friday night. There is also moisture
arriving aloft from the west. As a result, we should see more
widespread light snow fill spread across the area Friday and
Friday night.

There is still uncertainty as to how long the cold remains, but
trends have been for longer (e.g. into Sunday) before moderating
early next week.

&&

.SHORT TERM /Through Wednesday/...
Issued at 210 PM MST Tue Jan 20 2026

Perhaps the driest airmass of the season was overhead today. A few
reliable stations reported dew points less than -30F, with many
others in the -10 to -25F range across South Park and southern
Foothills. There is quite a moisture gradient across the I-25
corridor today, with well-mixed areas in the southwest side of
Denver sitting in the low 50s (with dew points near 0 to -10),
while Longmont and Greeley never fully eroded the surface
inversion and remain in the upper 30s to mid 40s (with RH near
40-50%). Understandably, guidance has not handled this well and I
suspect those struggles will continue into this evening.

Zooming out a bit, a shortwave is tracking across Wyoming this
afternoon, and should race into the Central Great Plains by
tonight. This will only provide a glancing blow, in the form of a
very weak cold front. This should lead to temperatures ending up a
few degrees cooler during the day tomorrow. Unfortunately, surface
moisture still looks meager tomorrow... and we`ll see elevated
fire weather conditions across South Park/Front Range
Foothills/I-25 corridor where RH will likely fall back to the
single digits. The recent snowfall has provided just enough fuel
moisture to avoid any fire weather highlights.

&&

.LONG TERM /Wednesday night through Tuesday/...
Issued at 210 PM MST Tue Jan 20 2026

Longwave upper level trough will be over the Hudson Bay and Great
Lakes region the last half of the work week and into the weekend.
Northerly flow on the backside of the trough will push arctic air
southward. Colorado looks to be on the edge of the arctic air.
Typically we`ll see these arctic airmass advance southward along
the Continental Divide, which should result in at least a couple
cold days for the Front Range and eastern plains.

For Wednesday night and into Thursday, a weak cold front, more so
a wind shift to the northeast, is expected over northeast
Colorado. Colder air slowly seeps into the area with highs in the
30s expected over northeast Colorado. A strong surface high and
arctic air move into the Northern Rockies and Northern Plains
Thursday night. As the surface high slides southeastward.
Northeast low level flow will advect the arctic air into eastern
Colorado. Friday is expected to be cloudy and cold with highs in
the teens to mid 20s. The airmass moistens enough for light snow
and/or flurries for Friday night. There`s no strong lift and
limited moisture, so snowfall is expected to be light, less than 2
inches.

The temperature forecast becomes much more uncertain for Saturday
(and beyond). The arctic is expected to remain over the area
Saturday, which will result in continued cold temperatures with
highs in the teens and 20s for Saturday. However, there are some
ensemble members of the ECMWF and GEFS that scour out the colder
air and highs climb into the 40s. Think this is a little
aggressive bringing the warmer air and expect Saturday to be a
chilly day. The uncertainty continues for Sunday. Most models show
a lee side surface trough forming over eastern Colorado. This
would bring west winds and scour out the colder air. The 12Z GFS
changed and now shows a second shot of arctic air, which would
keeps highs well below freezing on Sunday. Will keep the forecast
closer to ensemble mean which warms temperatures into the 30s for
Sunday.

For Monday and Tuesday of next week, flow aloft becomes more
zonal. This brings milder air back to the region with temperatures
climbing into the 40s for Monday and possibly 50s for Tuesday.
Forecast remains dry for these periods with the lack of moisture
and forcing continuing.

&&

.AVIATION /12Z TAFS through 12Z Thursday/...
Issued at 434 AM MST Wed Jan 21 2026

VFR conditions are expected through this TAF package. Winds this
morning will generally be typical drainage flow. Winds will become
more variable around 17Z, with winds turning more E/SE for the
afternoon. KBJC could see occasional westerly gusts this
afternoon, with light easterly winds mixed in. A weak front is
expected to move near the terminals around 1Z to 2Z this evening.
The front should be much weaker than the one we saw yesterday,
but we will be monitoring the potential for some gusty ENE winds
as the front moves through, especially at KDEN. After the front,
winds will become lighter and more variable.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...20
SHORT TERM...Hiris
LONG TERM...12
AVIATION...AP

NWS BOU Office Area Forecast Discussion