328
FXUS65 KBOU 202017
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
117 PM MST Thu Nov 20 2025

.KEY MESSAGES...

- Snowfall up to 4 inches for the mountains with the highest
  amounts in the Front Range Mountains through Friday.

- Widespread rainfall for the plains through early Friday with
  only a slight chance (15%) of snow for the Denver metro and
  plains. The northern plains and Palmer Divide have a 30-40%
  chance of seeing snow with minimal snow amounts expected.

- Another precipitation event is possible late Sunday.

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

&&

.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 /18Z TAFS through 18Z Friday/...
Issued at 1032 AM MST Thu Nov 20 2025

An incoming storm system will bring lowering clouds and rain showers
late this afternoon through Friday morning. Ceilings are expected to
fall below 6000 feet 23-02Z with rain showers developing.
Ceilings continue to fall overnight dropping below 1000 feet with
visibility lowering to 2-5sm as well with light rainfall. These
IFR conditions continue into Friday morning. Can`t rule out fog
with visibility a quarter mile or less, but chances are less than
20 percent. Low clouds slowly lift Friday, but don`t scatter out
until the afternoon, 21-23Z.

&&

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

&&

$$

DISCUSSION...20
AVIATION...12