535
FXUS65 KBOU 172309
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
409 PM MST Mon Nov 17 2025

.KEY MESSAGES...

- Snow showers in the northern mountains and scattered travel
  impacts linger into this evening.

- Strong, gusty winds along the Front Range diminishing this
  evening.

- Better agreement for the Thursday to Friday storm system, but a
  fair amount of uncertainty still exists regarding details.
  Accumulating snow (mainly light) is likely (60-70%) for the
  Palmer Divide, foothills, and mountains. A few colder model runs
  still have a little snow (20-30% chance) for Denver/portions of
  the plains.

- Temperatures return to below normal Thursday and Friday. Slight
  recovery into the weekend to near/just above normal.

&&

.DISCUSSION /Through Monday/...
Issued at 201 PM MST Mon Nov 17 2025

Water vapor satellite imagery showing the closed low over western
Nebraska. This low will continue to pull away from Colorado the rest
of this afternoon and tonight. Mountain snow showers will decrease
through this evening ending around or a little after midnight. Up to
3 additional inches of snowfall will be possible over the northern
mountains. Gusty west to northwest downslope winds east of the
mountains is drying the airmass. These gusty winds continue through
sunset across the urban corridor and eastern plains. Gusts of 40-50
mph may linger into the evening hours in the foothills. Added a
chance for showers over the northeast plains for this evening where
wrap around showers could clip the far northeast part of the state.

Upper level ridging quickly replaces the low and will be over
Colorado late tonight and Tuesday. Dry conditions return to the
region overnight and continues through Tuesday. Temperatures will
be above normal with highs in the upper 50s to lower 60s across
northeast Colorado.

The upper level ridge will remain over the forecast area through
Wednesday, as the next storm system moves into or just off the
coast of southern California. That means one more mainly dry day
Wednesday, with only a light snow shower or two possible in the
mountains. Temperatures should stay a good 5-8 degrees above
normal.

Regarding our potential storm for Thursday and Friday, there is
more agreement in the models today. It appears any interaction
with the U.S./Canadian border shortwave is essentially off the
table. This means we can mostly focus on the southern stream
energy, and eventual evolution of the SoCal low. The kicker of
this low pressure system will be yet another low that drops south
along the Pacific Coast. As it does, there is now better agreement
that the SoCal low will gradually weaken as it moves east/
northeast across Arizona and then toward the CO/KS/OK border area.
The ECMWF ensemble averages were a bit farther north - leaning
toward southeast Colorado, while the GEFS averaged a bit farther
south toward the OK panhandle. Almost all had some negative tilt,
with only a few showing signs of restrengthening when the storm
system moves into the High Plains. Most solutions had the low
pressure system shearing a bit and weakening, as it does finally
have some interaction with the northern branch of energy. Thus,
while the odds of precipitation are increasing given better
confidence in the eventual track and intensity, the previous small
(10-20%) chances of a more significant storm are decreasing.

The latest ensemble guidance shows us just that. The ECMWF
ensemble is almost unanimous showing modest QPF (0.25-0.60" in the
25-75th percentiles and 0.1-0.8" in the 10th-90th) along the
Front Range. East central CO had somewhat higher amounts (0.4-1.0"
in 25-75th, and ~0.3-1.3" for the 10th-90th percentiles). Amounts
and confidence of measurable precipitation decreased farther west
and northwest. Meanwhile, the GEFS (and GFS) was less confident
about the northward extent of precipitation and overall had about
half the members and half the QPF of all other ensemble systems.
The NBM has done well increasing the chances of precipitation to
reflect the latest ECMWF trends, so PoPs in this forecast package
are the highest we`ve seen for this system as we continue to trend
up with the chances of measurable precipitation. At the same
time, considering just a few colder/stronger runs it`s looking
more like mostly rain for Denver and points northeast, but still
some snow could mix in by late Thursday night and Friday morning.
The odds of any accumulation for Denver are still sitting at
20-30% with a high probability if it did snow for only light
accumulations as temperatures would only hover near freezing for a
few hours. Higher elevations, including the Palmer Divide would
have a 60-70% chance of accumulating snow, with a lower
probability (20-30%) of 6" or more over the Palmer Divide.

There is good agreement that precipitation will wind down Friday
as the trough continues to shear and move east into the Central
Plains. Temperatures will be cooler for this period with the
clouds and precipitation, and highs will stay a few degrees below
climatological norms.

We`ll likely settle into upper level ridging by the weekend, as
there is good agreement that we`ll be stuck in between an upper
low dropping into Baja and any northern stream energy. This
typically brings us dry weather with near normal temperatures, and
that`s where our forecast will reside for now Saturday through
next Monday.

&&

.AVIATION /00Z TAFS through 00Z Wednesday/...
Issued at 406 PM MST Mon Nov 17 2025

Winds were WNW late this aftn with gusts up to 30 mph at BJC.
Winds will slowly decrease by 01z and should become more WSW.
However BJC may still see some gusts up to 30 mph thru 02z.
Overnight winds will become drainage at APA and DIA by 03z
with WNW winds at BJC.  On Tue, winds will become more SE at
all the airports by 19Z.  Otherwise VFR conditions thru the
period.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST this afternoon for COZ031.

&&

$$

DISCUSSION...12/20
AVIATION...RPK