654
FXUS65 KBOU 171132
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
432 AM MST Mon Nov 17 2025

.KEY MESSAGES...

- Fast moving storm system will bring snow to the mountains this
  through the rest of the day today. Continued travel impacts
  likely, highest impacts for Rabbit Ears Pass.

- Strong, gusty winds across the Front Range Mountains/Foothills
  today.

- Still watching potential for a stronger early season storm next
  week, but considerable uncertainty. It will be cooler through
  the week ahead.

&&

.UPDATE...
Issued at 325 AM MST Mon Nov 17 2025

Previous forecast is still largely on track tonight. The center of
the passing closed 500mb low sits over far southwestern Wyoming
this morning, and should continue to drift eastward through the
day. There hasn`t been much of a mountain wave yet, but guidance
still has gradually increasing winds across most of the Front
Range as we go through the afternoon hours today. While the
overnight period has been relatively quiet across the mountains,
orographic snow should pick back up as the upper low pushes east
later this morning.

For later in the week, our forecast confidence remains very low.
There continue to be substantial run to run changes across most of
the medium range guidance, which is unsurprising given the number
of moving pieces in this timeframe. We did nudge up PoPs up a bit
more with a majority 00z ensemble members producing at least some
QPF across the metro. I remain skeptical about the chances of
wintry precipitation for our lower elevations, but the potential
for some meaningful precipitation is a welcome change.

&&

.DISCUSSION /Through Sunday/...
Issued at 238 PM MST Sun Nov 16 2025

The closed upper low moving into western Utah will push northeast
tonight and move across southern Wyoming Monday morning. Moderate
QG lift on the front end of this system will bring what should be
an organized area of precipitation across our mountains starting
mid evening. We see that as the best opportunity for snow
accumulation and travel impacts in the mountains of the I-70
Corridor/Summit County. The main moisture band then continues to
lift northeast with some drying and tapering off of the snow
showers late tonight. However, orographics strengthen from a more
favorable westerly component in the wake of the upper low, and it
still appears moisture profiles will be favorable for additional
accumulations in most of the mountains north of the I-70 Corridor
through at least mid afternoon Monday. We`ll maintain the Winter
Weather Advisory for the mountains from Rabbit Ears Pass northward
where latest guidance supports 4-10" snowfall with locally higher
amounts. We still think most of the northern Front Range will see
3-6". Meanwhile, the I-70 mountain corridor and Summit County
most likely sees 0.5 to 3" amounts due to poor orographic
contribution when the best moisture comes across this evening,
and then residing south of the main mid level moisture plume on
Monday when the better orographics finally arrive.

With regard to winds, the potent upper level trough moving to our
north and east and strengthening gradients/flow aloft will mean
strong, gusty winds developing along the Front Range. There are
still indications we see a mean state critical layer develop by
09Z tonight, and cross sections show cross mountain component
strengthening to 30-35 kts. Typically, if these scenarios unfold
we can double that magnitude, so peak gusts could reach 75 mph in
local spots 09Z-12Z. Otherwise, we`ll have to rely on the brute
force and modest stability at mountain top to generate high winds.
For now, the stable layer appears limited by mountain snowfall and
an elevated stable layer through most of Monday, so the chances
of High Wind Warning criteria being met are likely confined to
localized areas in the Boulder County foothills. We`ll message
that accordingly and not issue a High Wind Warning at this time
since more widespread high winds are not anticipated. We`ll
continue to monitor as the night progresses of course, but latest
models were also trending slightly weaker.

Tuesday will feature drier and calmer conditions as an upper level
ridge bumps up across the forecast area. Temperatures will remain
cooler than what we`ve recently experienced to be sure, but still
a few degrees above normal.

We`re pretty certain Wednesday will still be a relatively dry and
mild day, still caught under some ridging as the next storm system
slides slowly across the SoCal region. That`s where the fun
begins.

A considerable amount of uncertainty exists with how this upper
low is treated, and any interaction with the northern piece of
energy that comes out of the parent trough and ejects eastward
across the U.S./Canadian border. A bundle of solutions exist;
some showing an open trough kicking slightly faster across the
forecast area, some ejecting the low to the E/SE into Texas, a few
still incorporating the northern stream energy into the SoCal
low, and still a few others (the potentially important ones)
kicking the upper low E/NE across northern New Mexico into the OK
Panhandle. The latter solution would favor a more significant
precipitation event, but even some of those would be too far south
to bring significant precipitation into the Front Range. IF, and
that`s a relatively big IF, the stronger slightly northern track
could verify then we would see more impactful weather. The latest
ensemble data shows about 25-35% of the ECMWF and AI members push
out this solution with heavier precipitation and measurable snow
back to Denver, while about 50% have lighter precipitation and
minimal if any snow, while the other 15-25% are relatively dry.
GEFS numbers have significantly lower potential.

Whatever the case, there is a LOT of uncertainty at this point
so we need to stay away from picking/choosing any one particular
run or even cluster of models (which are fairly evenly split at
this time). While it will be difficult to phase the energy
together at any given point, this storm system still bears
watching. Given this unique and relatively unstable synoptic
setup, we may not know much more for a couple days yet - stay
tuned for the latest.

There is still some weak trailing troughing possible into Saturday,
but overall drier and slightly warmer (near normal) weather
should return at some point next weekend.

&&

.AVIATION /12Z TAFS through 12Z Tuesday/...
Issued at 428 AM MST Mon Nov 17 2025

VFR through the TAF period. Main concern will be periods of gusty
winds beginning later this morning and continuing through most of
the afternoon. Guidance develops deeper mixing near 18z, with some
gusts of 30-35kt possible. Best chance of seeing >30kt gusts is at
BJC with slightly lower chances for DEN/APA. There are a few hints
from guidance that we`ll see one or two channels of stronger gusts
develop with lighter, potentially easterly winds in between. Did
think about turning the prevailing gusts at DEN into a TEMPO, but
don`t have enough confidence to change it.

We should see a quick decoupling near sunset/00z with wind gusts
quickly diminishing. Drainage flow should redevelop later in the
evening and continue into Tuesday morning.

&&

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

&&

$$

UPDATE...Hiris
DISCUSSION...20
AVIATION...Hiris