489
FXUS65 KBOU 220527
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1027 PM MST Fri Nov 21 2025

.KEY MESSAGES...

- Clearing tonight, but areas of dense fog in valleys.

- Another light precipitation event is possible Sunday and Sunday
  night, with light snow above ~7,000 ft and light rain lower
  elevations.

- Becoming windy Monday to Tuesday, and turning colder.

- Some moderation with diminishing chances of any snow through
  Thanksgiving.

&&

.DISCUSSION /Through Friday/...
Issued at 1242 PM MST Fri Nov 21 2025

Lingering showers will continue to diminish through the rest of
the afternoon. Spotty snow accumulations in the mountains and
higher foothills could still reach a half inch or so from small
convective showers. Otherwise, we`re already seeing some breaks
in the clouds near the Front Range, and that clearing trend will
continue into this evening as a lee trough develops and light
downslope ensues. The clearing skies and trapped low level
moisture (current dewpoints near 40), will support areas of fog
overnight to mid morning Saturday. Some of this will likely be
dense in low lying valleys so we`ll monitor threat for possibility
of a Dense Fog Advisory should dense fog become more widespread.
The most prone areas would be the South Platte and Cache La Poudre
valleys north of Denver, while high mountain valleys may also see
some fog given large T/Td crossovers. Most of Denver metro
expected to stay fog free given sufficient downslope drainage
winds.

After morning fog, Saturday will feature a return of sunshine,
helping boost temperatures several degrees above normal for
daytime highs. Winds will be light thanks to an upper level ridge
over the forecast area.

We`re still keeping an eye on Sunday`s weather as yet another
ejecting upper level low moves this way. Ensemble guidance still
suggests this upper low lifts from Baja northeast across the
forecast area, with the average track moving across east central
Colorado. Once again, that puts the highest probability of best
lift/moisture combination over the southern and eastern sections
of the forecast area, with points northwest of Denver seeing lower
chances of precipitation. Overall, we think precipitation will be
mainly on the light side per ensemble guidance, but a few runs
still have more than 0.50" of rain (~20%). Snow levels still
average 7,000-7,500 feet in output, and that looks reasonable give
the only cold air will be associated with the upper low itself.

What has changed in the longer term starts Monday. There is now
more agreement that a fast moving shortwave arrives late Monday
and Monday night from the Pacific Northwest. That means stronger
pressure gradients, stronger winds, and a quicker arrival to the
next chance of snow in the northern mountains. It will also spell
colder temperatures. Regarding winds, the local Sangster output
from deterministic models has shown an increasing trend, and the
same can be said for ensemble output. While most guidance is
still well below high wind criteria, it`s something to note that
the trend is increasing and there`s a low (20% chance) that a High
Wind highlight may be needed depending on later model trends and
output.

More changes also surround the pre-Thanksgiving travel period of
Tuesday and Wednesday. While strong, gusty winds may continue into
Tuesday, any mountain snowfall should be winding down as flat
ridging and drying start to build in. That`s a notable change
since yesterday, but the trend is for better mountain travel
weather. Wednesday and Thanksgiving have also trended warmer due
to more ridging in this period. Still something to watch, however,
as this pattern can be notorious for embedded weak shortwaves and
bouts of orographic snow, but the trend remains our friend for
now. The opposite may hold true for return travel, as ensembles
have shifted the next chance of snow along with much colder
temperatures toward the latter half of Thanksgiving weekend.
While recent model performance has been relatively poor and
unstable, this something to watch as it could offer up the first
taste of true winter cold and snow for our forecast area.

&&

.AVIATION /06Z TAFS through 06Z Sunday/...
Issued at 1027 PM MST Fri Nov 21 2025

VFR through Saturday and into Sunday morning. There will be a fog
bank north of DEN tonight, but confidence is pretty high that the
drainage winds out of the south will keep it north of KDEN.
However, as typically occurs with drainage winds, they weaken
after 12Z in the absence of any broader pressure gradient. When
that happens, the fog bank itself generates a push to the south.
High res models keep it just north of BJC and DEN but it will
likely get close enough to mention here between 12-15Z. 10-15%
chance the fog gets to DEN and BJC during those hours, not enough
to include in the TAFs just yet. The good news is that we will be
able to use GOES-E to detect the fog bank early Saturday morning.
APA will avoid any fog tonight into the morning hours.

During the early afternoon (19-20Z), expect ESE winds at the
terminals, around 10 kt at BJC and APA and 12-15 kts at DEN. Winds
will do their diurnal business going SE at 03Z, then drainage
(south to SSW) after 06Z at 6-10 kts at DEN and APA. BJC will go
to light and WSW.

&&

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

&&

$$

DISCUSSION...20
AVIATION...Schlatter