223
FXUS65 KBOU 201129
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
429 AM MST Thu Nov 20 2025

.KEY MESSAGES...

- Light accumulating snow is likely (65-75%) across the Front
  Range mountains and foothills. Generally 1-6" of snow is
  expected with the highest amounts in the Front Range Mountains.
  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.

- The plains will see widespread rainfall late Thursday through
  early Friday. Amounts up to an inch of rain are possible,
  especially across far eastern/northeastern Colorado.

- Another rain event is possible late Sunday across the plains.
  Light snow is likely in the mountains and foothills.

- Turning cooler around Thanksgiving with the potential for a
  couple very light snowfall events during the latter half of
  Thanksgiving week.

&&

.UPDATE...
Issued at 228 AM MST Thu Nov 20 2025

Silly me for thinking there`d be a model consensus 18 hours before
precipitation is set to arrive.

Water vapor satellite tonight shows the center of our primary
upper level low lifting northward into south-central Arizona, with
the second upper trough dropping into the Pacific Northwest.
Guidance still doesn`t really know what to do with the former of
these two features as it lifts pivots northeastward today, before
it runs into some confluence over the Central Great Plains and
shears out. Whatever happens to the upper low over the next 12
hours or so will have substantial impacts on the strength of the
surface and 700mb lows as they develop over southeastern Colorado,
and subsequently the amount of vapor transport (Gulf moisture)
that reaches the CWA. Several of the popular CAMs were quite
aggressive tonight, deepening a 1008mb or so surface low in the
Oklahoma panhandle, and unsurprisingly threw a lot of
precipitation into the forecast area. On the other hand, the GFS,
along with many of its global deterministic counterparts, has
trended notably weaker with the upper trough and struggle to
produce much precipitation west of I-25 with maximum QPF values
generally less than an inch across the plains.

As a whole, the forecast hasn`t changed much, but there are at
least a few things to note. First, I did both increase PoPs and
decrease QPF, for similar reasons as the day shift yesterday. It
is possible that there is briefly some convective elements early
in the evening as some cross-sections support some CSI over the
metro, but the overall trend in QPF can`t be ignored. Similarly,
that also has resulted in a little less snowfall across the
Foothills and Palmer Divide. Given lighter precipitation rates and
a marginal thermal environment, travel impacts are expected to be
limited to areas above around 6500ft. No plans for an advisory
unless we see a rapid shift towards a stronger/wetter solution
there.

Beyond this current storm system, we`ll have the second cutoff low
meander into the CWA by Sunday... with chances for rain and some
higher elevation snow yet again. Surprisingly there`s actually
better agreement here than in the near term period. Northwesterly
flow aloft is expected to develop sometime next week with a
couple of chances for snow across the forecast area. NBM might be
too cold for the Thanksgiving time period but we`ll worry about
that later.

&&

.DISCUSSION /Through Wednesday/...
Issued at 250 PM MST Wed Nov 19 2025

It`s hard to believe it`s the week before Thanksgiving and we will
be talking about two rain events for the Denver metro. But it`s
been a warm month that`s running 8.5 F above normal in Denver.

A trough that will bring precipitation to our area on Thursday is
currently over the California/Arizona border. There are plenty of
thunderstorms in Arizona which is indicative of the moisture in
the area. This trough will weaken, become more negatively tilted,
and will end up in eastern Colorado by Friday morning. A wave of
precipitation is expected to form over southeast Colorado Thursday
morning and will become more widespread and intense as it moves
northward into our forecast area. A deformation zone on the
northwest side of the trough will help to keep the precipitation
going in northeast Colorado through Thursday night and into
Friday. The difficulty will be determining how much precipitation
will fall and where the heaviest amounts will be. Models like the
NAM and HRRR have consistently been forecasting significant
precipitation for November standards. Each model has a wide swath
of rainfall around 1.5" across the plains. Meanwhile, the ECMWF
has been consistent with showing about a quarter inch of rainfall
in the Denver metro and around a half inch of rain across the
plains. The forecast was trended towards the ECMWF for QPF amounts
and the PoPs were increased across our CWA since the likelihood
of precipitation is increasing. While the QPF was trended towards
the ECMWF, the higher forecast QPF amounts are certainly possible
given the ample moisture arriving in our area with 40+ F dew
points expected.

The other forecast uncertainty in this event will be
precipitation type and snow level. As previously mentioned, dew
points in the low 40s will advect over the eastern plains and this
will mean precipitation will likely (80% chance) fall as all
rain. However, if precipitation amounts are more intense that
expected, areas near the Cheyenne Ridge and Palmer Divide could
receive some light snowfall late Thursday night. Across the
higher terrain, the snow level will be around 7,000-7,500 feet.
The Front Range Mountains and higher Foothills will see 1-6" of
snow. If the higher end precipitation values occur, snowfall
amounts could reach up to 10" especially in Rocky Mountain
National Park.

Brief ridging will move over Colorado late Friday into Saturday.
Friday night through Sunday morning will be dry with slightly
above normal temperatures.

The model trend has been very consistently moving a cut-off trough
over the Desert Southwest farther north on Sunday. The majority of
models take the center of the 500 mb trough into southeast
Colorado. This will bring a chance of precipitation to our
forecast area. The latest NBM doesn`t have this new data in it
so PoPs were increased on Sunday night to include a 30-40% chance
of precipitation across most of our area. This system will be
similar in regard to precipitation type as the first one. Rain is
likely across the plains and light snow is possible in the
mountains.

A period of ridging will move over Colorado on Monday and into
Tuesday with dry weather and normal temperatures expected. A
trough will bring cooler temperatures by Thanksgiving with below
normal temperatures expected. There will be multiple chances of
very light snowfall during the latter half of next week.

&&

.AVIATION /12Z TAFS through 12Z Friday/...
Issued at 426 AM MST Thu Nov 20 2025

VFR conditions likely to prevail most of the day today, with lower
ceilings developing near or after 00z. Guidance is quickly
trending drier for the terminals, which would also delay the
arrival of MVFR/IFR cigs this evening. There`s still a chance of
some SHRA this afternoon but lower chances than previously
expected. Much better chances of IFR conditions after 06z
continuing into the first half of Friday. Winds should transition
to the northeast by the early afternoon and gradually turn towards
the north this evening and tonight.

&&

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

&&

$$

UPDATE...Hiris
DISCUSSION...Danielson
AVIATION...Hiris