896
FXUS65 KBOU 261923
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
123 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 /18Z TAFS through 18Z Tuesday/...
Issued at 1215 PM MDT Mon Oct 26 2026

Current GOES-19 satellite imagery shows the stratus deck that
affected the sites this morning breaking up with the south metro
(KAPA) seeing the most improvements so far. Still, with the
saturated ground from the overnight rainfall/mist and low-level
moisture, clouds will have a difficult time fully scattering out
this afternoon. Therefore, we expect a sct deck around 1500 ft AGL
to 3000 ft AGL through mid-afternoon, but some improvements look
possible as we get to late in the afternoon. KAPA should have
fewer clouds than the other two sites. Winds this afternoon will
turn to the east and should remain under 12 kts.

Another night of fog is looking increasingly likely (>70%) at
KDEN and KBJC with 50/50 odds at KAPA. BUFKIT and model soundings
continue to point to saturated low levels with dewpoint
depressions at or under 1 degree. A Denver Cyclone is progged to
develop to the north of the three sites this evening and move off
to the northeast. This would cause a westerly component to the
wind at all three sites with light and vrb winds as we get into
Tuesday morning. In turn, short-term guidance is in very strong
agreement that fog could rapidly develop this evening as early as
6-8z from north to south on the north/west side of the cyclone.
The period of highest confidence at KDEN for visibility around 1/2
SM and IFR/LIFR restrictions is from 9z through about 14z. There
is a ~30% chance that visibility could even drop as low as 1/4 SM
with vv001 causing further restrictions. Generally, the same
timing is expected for KBJC with only slightly higher
visibility/ceilings than KDEN. At KAPA, winds could be a little
more southerly (downslope), which would lower overall chances for
impactful fog directly at the terminal. Otherwise, if winds do
keep more of a westerly component, fog/low ceilings/lowered
visibility are in play there as well.

The fog and low ceilings should start to lift by about 15z Tuesday,
but sct clouds around 1000 to 2000 ft AGL look to stick around
for a few more hours. VFR conditions appear possible by 18-20z
Tuesday afternoon as skies clear. Winds turn to the east for
Tuesday afternoon before becoming vrb by the evening.

&&

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

&&

$$

DISCUSSION...20
AVIATION...MV

NWS BOU Office Area Forecast Discussion