748
FXUS65 KBOU 270011
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
611 PM MDT Mon Oct 26 2026

.KEY MESSAGES...

- Areas of fog, some dense, across the plains and I-25 Corridor
  tonight into Tuesday morning.

- Warmer and mostly dry much of this week.

- Unsettled weather potentially returning late in the weekend and
  early next week, with a 20-30% chance of season`s first snow in
  lower elevations toward Tuesday.

&&

.DISCUSSION /Through Monday/...
Issued at 123 PM MDT Mon Oct 26 2026

The upper level trough that brought the overnight/early morning
rain and mountain snow is pushing well to our northeast, with
drier and more subsident airmass building in behind it. However,
abundant low level moisture remained in place east of the Front
Range, with the stratus deck only slowly burning off. While we do
expect more clearing through the late afternoon hours, areas of
low clouds and fog will redevelop tonight in the moist boundary
layer. This will be a hybrid radiational/advection fog event,
with contributions from a developing weak Denver Cyclone. The
expected location of the cyclone developing near/south of metro
Denver and pushing slowly northeast overnight into early Tuesday
morning favors fog over the eastern and northern plains, but then
also wrapping around the back side of the cyclone down the I-25
Corridor into at least the northern suburbs by/shortly after
midnight. There`s a 50-60% chance it moves as far south as the
southern Denver suburbs before daybreak. Given the hybrid event
and relatively narrow T/Td spreads, we think some areas will
experience dense fog. It`s quite difficult to narrow the exact
locations of thickest fog development, but something to watch for
the overnight and early morning hours with potential for a Dense
Fog Advisory. We`ll continue to monitor through the evening and
overnight.

On Tuesday, we`re not sure that we`ll see the magnitude of
warming we earlier anticipated. That`s because of the morning
stratus and fog, and lack of lee troughing. We`ve generally cut
temperatures a few degrees across the lower elevations but still
mostly lower to mid 60s for highs (but a 30-40% chance we only
hit the mid to upper 50s over the eastern plains). What we are
more certain about is that tomorrow will start a 3-4 day stretch
of dry weather.

That dry weather will be courtesy of drier and brisk west to
southwest flow aloft. There will be warm advection and flat
ridging by Thursday, which should support highs pushing to near
70F across the plains and I-25 Corridor.

Ensembles are still showing a subtropical push or partial remnants
(or at least water vapor transport) of Tropical Storm Vance in
the eastern tropical Pacific getting drawn up as early as Friday.
However, the main impacts of this would very likely (>80%) chance
stay to the east of our forecast area. We`ll only have a slight
chance of showers reaching the far eastern plains by late Friday.

A larger trough along with a possible subtropical moisture
connection/jet off the central and eastern Pacific reaches the
far southwest U.S. by late Saturday and Sunday. While that is
fairly well agreed upon by ensemble systems, models diverge
significantly by the time we reach Sunday into early next week.
Yes, there is general troughiness and storminess expected, but
some models move the trough through as an open or even shearing
wave, while others develop a deep closed low somewhere between the
Midwest and Colorado. It was interesting to note the EPS showed a
rather marked increase in precipitation and even snow potential
as we head toward Tuesday of next week, while the GEFS showed no
discernible trend. The EPS had close to 30% of the members
showing snow for Denver and the plains, while GEFS supported much
lower odds (10-20%). Some of these runs, of course, were much
colder than the vast majority of the ensembles, as evidenced in
the large temperature variations (25th-75th percentiles from highs
in the mid 40s to mid 60s for Monday and Tuesday, but full range
of outcomes from highs in the upper 20s to lower 70s). Stay tuned
for the latest trends and what could maybe, just maybe, be our
first snowfall in the lower elevations should the deeper/slower
solutions verify.

&&

.AVIATION /00Z TAFS through 00Z Wednesday/...
Issued at 547 PM MDT Mon Oct 26 2026

Current observations shows the Denver cyclone slightly stronger
than previously anticipated, with easterly winds of 9-12 kts over
DEN and slightly stronger at APA. For this reason, have increased
winds accordingly at both airports, with speeds gradually
weakening this evening and tonight as the cyclone moves
northeast. For BJC, generally light east/northeast winds remain
on track before transitioning more northerly/northwesterly
tonight.

Fog is still likely for DEN and BJC this evening, although
guidance has been hinting at an earlier onset timing this
afternoon. Have bumped up impacts to visibility beginning 03Z with
patchy fog, although we could start seeing it as early as 02Z.
Visibilities will then drop drastically by 06/07Z (down to as low
as 1/4SM at DEN) with only small improvements by 09/10Z. As
daytime heating occurs, fog will clear out by 16/17Z Tuesday
morning. There is still some uncertainty with fog at APA this
evening and tonight, as the airport could be just north of
stronger southerly winds with weaker westerly winds. Have opted
in to keep west winds in tonight, with fog as early as 07Z through
early morning. However, if the stronger southerly winds stick
around tonight, APA would likely not see fog.

Generally light and VRB winds expected for all terminals on
Tuesday morning with clearing skies by the afternoon. Short-range
guidance does favor a cyclone forming again, with increasing
easterly winds (8-11 kts) by 20/21Z. Some uncertainty with the
winds at APA in the afternoon, and will depend on where exactly
the cyclone forms (light southwest winds vs light easterly winds).


&&

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

&&

$$

DISCUSSION...20
AVIATION...MAI

NWS BOU Office Area Forecast Discussion