632
FXUS65 KBOU 211135
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
435 AM MST Fri Nov 21 2025

.KEY MESSAGES...

- Light snow is expected across the high country with an
  additional 1-2" possible through this evening. Any travel
  impacts are expected to be limited to the higher passes.

- Light rainfall will continue into midday across the plains,
  with the best chance of seeing 0.1-0.25" additional rain coming
  east of a Sterling to Akron line.

- Another precipitation event is possible late Sunday into early
  Monday with snow above 7,000 ft and light rain across the I-25
  corridor and eastern plains.

- Turning colder next week especially Tuesday, with potential for
  one or two light snowfalls Tuesday - Thanksgiving.

&&

.UPDATE...
Issued at 317 AM MST Fri Nov 21 2025

Area radar has consistently shown the westward extent of the
precipitation shield from the weakening short wave trough is
having a hard time holding together. GOES-E has the trough moving
due north across western Kansas. Eventually it will move
northeast, most likely by later this morning into midday. As it
pulls northeast, it will take the QG upward forcing further east
too. But it will take its time so we will keep PoPs highest across
the northeast corner of Colorado into this evening. However, we
reduced PoPs significantly along I-25 and westward across the high
country given observational trends and the latest model trends
which also show any additional rain/snow amounts will be light
throughout today. It will remain rain below about 7,000 ft
elevation, and precip should end by early afternoon for most areas
of the plains other than the aforementioned northeast corner.
However, the latest CAMS redevelop weak convective showers over
the mountains and move them east. Instability is not impressive
and overall there should be subsidence across the western half of
our area as the trough pulls further away. But there is still
enough for 10-40% PoPs this afternoon for light snow above 7,000
ft. We are not expecting travel impacts from any of the snow
showers. It will most likely be too dry just off the deck for
anything to reach the ground across the I-25 corridor this
afternoon. It will be cloudy and cool all day given the the weak
easterly upslope flow. We left the temps alone for the most part,
with temperatures remaining in the mid 40s across the plains and
even in the mountain valleys.

We are still watching the next trough in line which looks to lift
northeast from southern Arizona late Saturday into northeast
Colorado by late Saturday. Ensemble output leads us to have some
confidence in the track going across the southeast part of our
CWA, which would result in a decent swath of precipitation just
north of the track Sunday afternoon into very early Monday. For
now, believe it or not, precipitation will be all rain below 7,000
ft. There isn`t a cold front to work with, and this storm system
was never that cold in its core, plus it will also be weakening as
it lifts northeast. But at least 3-4 days out it looks like some
snow for the central mountains and light rain for the plains and
I-25 corridor. Amounts are definitely uncertain this far out and
highly dependent on the track of the storm as well as how much
weakening occurs throughout the day Sunday. The one thing to
mention that is pretty certain is that once the trough moves into
Nebraska later on Monday, it drags a significant cold front out of
the northwest across our area after all the moisture has moved
out of the area and subsidence has taken over. Tuesday will be dry
but one of the colder days we`ve seen since spring, but if you`ve
been keeping score at home that isn`t saying much this fall. For
now high temps on Tuesday will struggle to hit 40 deg across the
plains (and many areas may stay in the 30s), with 20s to around 30
in the mountain valleys.

&&

.DISCUSSION /Through Thursday/...
Issued at 117 PM MST Thu Nov 20 2025

Water vapor satellite imagery showing an upper level low spinning
over southwest New Mexico at this time. This low quickly lifts
northeast into Kansas by Friday morning. This system taps into
gulf moisture and lifts it northward into eastern Colorado.
Precipitable water values climb above the 99th percentile over
northeast Colorado tonight. So plenty of moisture will be
available for rain/snow. However, there`s no cold air entraining
into this system to help strengthen it (or keep it from weakening)
and keeps precipitation type as rain across the lower elevations.
Model trends continue to lean towards less precipitation for
northeast Colorado. This is due to this system weakening as it
passes east of the area. Earlier models runs were stronger and
farther west with the 700mb low. This produced a longer period of
upslope flow and pushed ample moisture westward. We still expect
some rainfall with snow above 7000-8000 feet. Precipitation
amounts along the urban corridor and westward are expected to
generally be less than a quarter inch. Over the northeast corner
of the state, rainfall amounts still could exceed a half inch, but
likely come in under an inch. Some snow could be mixed in along
the Cheyenne Ridge and Palmer Divide, but no accumulation is
expected.

Precipitation decreases early Friday morning and ends for the most
of the area early to mid afternoon. The exception being, snow
showers lingering in the mountains through the afternoon. Expect a
chilly day with cloudy skies expected for most or perhaps the entire
day.

An upper level ridge will take hold Saturday and Saturday night,
bringing dry conditions and a return to slightly above normal
temperatures.

Ensembles are in good agreement and continue to support the next
upper level low lifting northeast from Baja and reaching the
forecast area late Sunday. While this is a bit of a stretch
lifting from that far south, it has been done before. In similar
fashion to this most recent storm, the upper low weakens lifting
northeast and would support mostly light precipitation. We will
have the highest chances of precipitation south and southeast of
Denver, with lower probabilities farther north toward Fort Collins
and points northwest. Given no cold advection other than the core
of the upper low itself, any precipitation on the plains and I-25
Urban Corridor would stay in the form of rain. A rain/snow mix is
still possible in the foothills/Palmer Divide, with mainly light
snow/minor travel impacts possible in the mountains.

That upper level low gets kicked to the east late Monday and
Monday night by another shortwave, but this one comes in from the
Pacific Northwest. There is good ensemble agreement in this
pattern shift - to a flat ridge axis near the Pacific Coast and a
trough in the eastern United States. However, west/northwest flow
is notorious for difficult to time shortwaves, and some of that
is already notable in individual members within the ensemble. For
example, the latest operational ECMWF has a shortwave moving in
Monday night - Tuesday already, but EC ensembles show a higher
probability of a stronger shortwave toward Thanksgiving!

One thing we are confident in is the general pattern, which means
colder than normal temperatures settling into the area Tuesday
through Thanksgiving, along with a couple opportunities of mainly
light snow. If embedded shortwaves end up stronger, then there is
a chance (20-30%) of a higher impact mountain snow/blowing snow
event the middle of next week. We will continue to monitor that
for potential Thanksgiving travel impacts.

&&

.AVIATION /12Z TAFS through 12Z Saturday/...
Issued at 435 AM MST Fri Nov 21 2025

CIG/VIS continues to be a challenge at DEN this morning.
Reasonably confident that CIG/VIS should stay between 4-6SM and
003-007 for CIGs through much of the morning. There isn`t much
that will be able to scour out those low clouds because of
continued weak winds from the north-northwest. Available high res
model guidance is pretty pessimistic about improvements until the
afternoon. The current TAF is not that pessimistic because there
has been less precipitation than the models predicted. Winds at
all the terminals will be light all day today and out of a
northerly direction between 340-020 deg until after 20 or 21Z when
they should go more east, but again remain between 4-8 kts. Light
rain or drizzle is possible through about midday but should not
have much of an impact on CIG/VIS, in fact at DEN if it rains the
VIS would improve and the CIG come up a few hundred feet. For the
12Z TAFS we have decided to go with a tempo group to handle any
rain/drizzle.

Visuals are expected to return after about 02Z, and that is also
when southerly drainage winds should begin at APA and DEN, but
5-8 kts is as strong we we expect them to be. Southwest winds
around 5 kts are probable at BJC overnight tonight. On Saturday,
visuals all day long and light winds out of the southeast look
likely.

&&

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

&&

$$

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