586
FXUS65 KBOU 221125
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
425 AM MST Sat Nov 22 2025

.KEY MESSAGES...

- Areas of dense fog in valleys through 9 AM, mostly in Weld and
  Morgan Counties. I-25 corridor from north metro Denver to Fort
  Collins will also see patchy fog this morning.

- 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.

&&

.UPDATE...
Issued at 321 AM MST Sat Nov 22 2025

Just a few adjustments to the forecast overnight. First, we
refined the areas of fog based on the latest CAMs and cams (see
what I did there). Webcams, GOES-E, and the HRRR all seem to have
a pretty good handle on the fog so far. For now, visibilities
don`t seem to be dropping down to 1/2 mile anywhere, thus am not
planning on a dense fog advisory but please use caution if you are
driving in Weld or Morgan Counties, and along I-25 from north
metro Denver to Fort Collins, US-85, I-76, or anywhere within 20
miles of Greeley.

A final target of opportunity is for the Sunday into early Monday
system. High res guidance is pretty consistent in the axis of
precipitation remaining east of I-25. A deformation zone/TROWAL
is expected to set up southwest to northeast when the trough
lifts northeast and wraps moisture around its northwest quadrant
late Sunday as it moves across northeast Colorado. Very little
precipitation is expected across the northern Front Range and the
Park/Gore Ranges, and thus reduced PoPs quite a bit for late
Sunday into early Monday. The I-25 corridor from Denver to the
Wyoming border is also looking much drier than previous model runs
were indicating, and that fits with the current storm track and
position of the TROWAL/deformation zone. The NBM hadn`t caught up
yet to this trend, and thus PoPs were trimmed to create a
dry/drier slot of sorts. PoPs were left alone from Douglas County
northeast to Fort Morgan/Sterling/Julesburg and points southeast
of there, where the best forcing will occur. All signs continue
to point to rain as the dominant P-type below 7,000 ft. The
latest thinking for snowfall amounts in the mountains are along
and south of I-70: T-4" are possible with the highest amounts
across the higher passes from Berthoud-EJM Tunnels-Loveland-
Hoosier Passes. Slick roads are possible across the higher passes
and across South Park starting late Sunday evening.

&&

.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 /12Z TAFS through 12Z Sunday/...
Issued at 425 AM MST Sat Nov 22 2025

VFR through at least midday Sunday. As expected, an area of very
low clouds/fog has developed north of DEN across Weld County. The
drainage winds continue to be 10-14 kts out of the south, which
will keep the fog/low clouds to the north as long as they
continue. They will weaken a little after 14Z, allowing the
fog/low clouds to begin sloshing southward towards BJC and DEN.
However, the Latest high resolution models have trended towards
keeping the fog/low clouds in Weld County. The time it gets
closest to DEN or BJC is 14-16Z. At this point it`s probably a
10% chance or less of getting to BJC or DEN. APA has zero chance
of fog this morning. The fog/clouds will dissipate by 16-17Z
regardless of where they are.

ESE winds should pick up after 19Z at 10-15 kts across the
terminals, continue into the early evening hours before they
weaken, and turn to the south with drainage flow after 03Z. The
drainage flow looks pretty robust at DEN and APA, expecting 10-15
kts at DEN, and up to 10 kts at APA. BJC should have light winds
all night.

Later Sunday afternoon rain chances increase, as do the chances
for CIGS to drop into the MVFR category.

&&

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

&&

$$

UPDATE...Schlatter
DISCUSSION...20
AVIATION...Schlatter