647
FXUS65 KBOU 181736
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1036 AM MST Tue Nov 18 2025

.KEY MESSAGES...

- Quieter weather today and tomorrow.

- Still sorting out the details of the late week storm system.
  Accumulating snow remains likely (60-70%) across the Front Range
  mountains and foothills, and across the Palmer Divide. Only a
  slight chance (<20%) of snow for the Denver metro and plains.

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

&&

.UPDATE...
Issued at 238 AM MST Tue Nov 18 2025

Fairly quiet weather is expected for the next couple of days as we
sit under a weak ridge, in between two cutoff lows. No significant
changes were needed to the forecast through Wednesday.

Forecast guidance is slowly coming into better agreement for our
late week storm, though there is still considerable uncertainty
for impacts to our CWA. The upper low currently located near the
central California coastline should continue to dive southeastward
over the next day or two, before pivoting back to the northeast
into northern New Mexico by Thursday evening. The ejection of the
lead wave is likely to be heavily influenced by a second, stronger
upper low that is expected to drop into the western CONUS.

Although there was fairly good alignment across the 00z
deterministic guidance, there are still rather large run to run
shifts across individual models with these two features. It is
also intriguing that the GFS Graphcast and ECMWF AIFS end up as
substantially drier solutions here. While our NBM (and our
forecast) PoPs continue to gradually increase in this period, it`s
worth noting that there are solutions where most of our CWA misses
out on meaningful precipitation. Perhaps there will be more
confidence here by Wednesday, but until then any more specifics
will have to wait.

&&

.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 /18Z TAFS through 18Z Wednesday/...
Issued at 1034 AM MST Tue Nov 18 2025

Forecast remains on track. VFR conditions will prevail for all
terminals through the TAF period. Drainage flow will back to a
more southeasterly direction shortly (next 1-2 hrs) before a
return to typical drainage pattern this evening.

&&

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

&&

$$

UPDATE...Hiris
DISCUSSION...12/20
AVIATION...BRQ