663 
FXUS65 KBOU 221820
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1220 PM MDT Tue Sep 22 2026

.KEY MESSAGES...

- Isolated chances for showers/thunderstorms Tuesday afternoon and
  evening. 

- A disturbance moves through Wednesday and Thursday bringing
  increased chances for showers/storms and cooler temperatures
  Thursday.
 
- Drier and warmer this weekend, but isolated chances for showers
  and thunderstorms in the evening are possible. 

&&

.UPDATE...
Issued at 248 AM MDT Tue Sep 22 2026

With a uniform low stratus deck advecting into our northeast
plains, as well as broken stratus over the Palmer Divide, have
introduced a mention of patchy fog into the forecast for the early
morning hours in these areas. Relatively robust drainage flow 
should pump the breaks on the status expansion in the plains very 
shortly, confining most of the visibility impacts to Logan, 
Sedgwick and Phillips Counties. Any fog should be relatively 
brief, lifting by mid-morning.

&&

.DISCUSSION /Through Monday/...
Issued at 1208 AM MDT Tue Sep 22 2026

Satellite imagery shows a few patchy low clouds over the eastern
Colorado plains and a quiet night ahead. Lows tonight will be in 
the low 50s at low elevations and 30s-40s for the mountains. 
Temperatures Tuesday afternoon warm up slightly but remain right 
at seasonal averages, with highs in the low 80s for the Denver 
metro. A shift to SW flow aloft will result in the return of 
monsoonal moisture for the mountains. As such, a few isolated 
showers and storms may develop over the high terrain late in the 
afternoon. The chance for showers over the Denver metro and east 
Colorado plains will remain very low (<20%). However, high-res 
model soundings do generally show inverted-V profiles which would 
indicate some potential for gusty winds (up to 35 mph) should any 
high-based/virga showers develop.

Deterministic and ensemble global model solutions are in fairly 
good agreement that a mid-level disturbance will track north from 
New Mexico to Colorado on Wednesday. Just to the east, a ridge 
will continue to build over the Great Plains with an anticyclone 
centered over Oklahoma, which will encourage steady S-SE flow at 
the low levels. The bulk of the moisture is expected to be 
stationed over New Mexico and southern Colorado. However, PWs in 
the 1.0-1.3" range will still be advected over the much of our CWA
east of the foothills. Such anomalous moisture this late in the 
season will be something to watch as a slight west or north shift 
in this setup would push the flash flooding threat into our area. 
At this time, it looks like the better chance for localized heavy 
rainfall in our area will remain over the east Colorado plains. 
For the Denver metro and I-25 corridor, Wednesday will likely 
still bring the best chance for scattered showers although the 
timing remains a bit uncertain. If dense cloud cover develops 
early in the day, this will limit instability considerably and 
lead to very isolated shower coverage. Regardless of cloud cover, 
there is a decent chance (55%) for at least a round or two of 
showers in the overnight hours as the right- entrance region of a 
jet streak provides additional forcing. West of the foothills, 
monsoonal moisture will be closer to seasonal values but still 
above normal, allowing for afternoon showers and storms to develop
with daytime destabilization.

Moisture at the low elevations will peak around Thursday morning 
and this is likely to limit instability for the day due to a low 
to mid level cloud deck and temperatures struggling to climb above
the upper 60s. Such limited instability will decrease shower 
coverage Thursday afternoon although scattered showers are still 
likely over the high terrain and eastern Colorado plains.

A weak shortwave will track through Colorado Friday afternoon and 
promote scattered showers and storms, mainly over the high terrain.
Ensemble guidance is in good agreement that Saturday and Sunday 
will be drier days with mostly sunny skies and temperatures 
running a few degrees warmer than normal. Uncertainty enters the 
picture early next week with some global model solutions 
suggesting an upper level trough or cut-off low, and others 
showing a return to ridging. Long-range ensembles do hint at a 
more amplified wave trend for next week.

&&

.AVIATION /18Z TAFS through 18Z Wednesday/...
Issued at 1154 AM MDT Tue Sep 22 2026

VFR conditions are expected to prevail through the TAF period.
Winds are currently light but slowly starting to settle on an
east-southeast direction, which should continue into the afternoon
hours. Most guidance still develops a few showers later this
afternoon, though ACARS soundings are still quite capped between
800-700mb. Didn't see a reason to change the existing PROB30,
though it was extended an hour further into the evening. A few
showers may linger into the early overnight hours along the Palmer
Divide, which should help winds transition back to drainage
directions after 03z.

A little more uncertainty in the forecast tomorrow. Most CAMs
develop a weak lee trough/cyclone across the Denver metro, leading
to a variety of possible wind directions by the late morning
hours. Winds at least look weak during this period with speeds
near or less than 10kt. Guidance again tries to develop additional
showers or storms in the afternoon, but there is considerable
spread across guidance in terms of precipitation potential.

&&

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

&&

$$

UPDATE...BRQ
DISCUSSION...AA
AVIATION...Hiris