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