058
FXUS65 KBOU 222046
AFDBOU

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

.KEY MESSAGES...

- Isolated to scattered showers/thunderstorms this afternoon and
  evening.

- A disturbance moves through Wednesday and Thursday bringing
  increased chances for showers/storms (40-70%) and cooler
  temperatures Thursday.

- Drier and warmer this weekend, but isolated showers and
  thunderstorms each afternoon and evening can`t be ruled out.

&&

.DISCUSSION /Through Tuesday/...
Issued at 242 PM MDT Tue Sep 22 2026

Water vapor imagery shows moisture starting to advect into
Southwestern Colorado associated with the disturbance in New
Mexico/Southeast AZ. Showers and storms are currently developing in
the higher terrain. With the influx of moisture in the southwest
flow aloft, more showers/thunderstorms are expected this afternoon
in the higher terrain. Isolated high-based showers/storms could
drift off the foothills and track eastward into the I-25 corridor
and Denver Metro (15-20% coverage), but scattered (25-35%) coverage
on the Palmer Divide. The eastern plains may also have a
shower/storm linger into the late evening. Models this afternoon
indicate DCAPE values in the 1000-1100 range, so gusty winds up to
~25-35 mph are possible with any showers/storms today. Forecast
soundings indicate the urban corridor remains limited in
instability, but MLCAPE is forecasted for 500-900 and MLCIN to be
quite minimal in the eastern plains so an isolated strong storm is
possible but quite low. High temperatures today will favor upper 70s
and lower 80s.

Deterministic and ensemble model guidance are in good agreement for
precipitable waters to increase Wednesday afternoon/late evening
bringing our highest moisture for the week. Additionally, models
indicate a shortwave moving through around Wednesday evening into
Thursday morning before transitioning out of our area rather quickly
by Thursday evening. The right entrance region of a jet streak
moving through in the afternoon should also provide some additional
lift. PWATs are expected across the forecast area in the 1.0-1.3
range with the highest values in the eastern and southern plains.
More southerly flow in the eastern plains is modeled Wednesday
afternoon advecting greater moisture into the area increasing
dewpoints near 60F while the Denver metro should be in the upper
50s. We still think the greatest chance for localized heavy rainfall
will remain over the east Colorado plains. This will increase rain
chances Wednesday afternoon (~30%) for the urban corridor before
increasing further towards the evening near 50-60% for most of the
night. We decided to increase chances for rain mostly for the
eastern plains into Wednesday night and Thursday morning since model
guidance favors the area. However, we are still concerned about
abundant cloud cover limiting instability leading to much less storm
coverage.

By Thursday morning low-level moisture will peak and cloud cover
will dominate much of the forecast area. Nonetheless a round of
showers/storms is modeled to move through Thursday morning in the
eastern plains (70-80%). Isolated storms could produce localized
heavy rainfall as warm cloud depths increase to 4,000-6,000 feet.
The urban corridor`s chances remain slightly below the eastern
plains while the higher terrain should see shower development.
Temperatures will only reach the upper 60s with the aforementioned
cloud cover. We will likely see a slight decrease in shower coverage
in the afternoon, given the expected earlier passage of the
shortwave and less remaining instability for the eastern plains.

On Friday, another weak shortwave will move through Colorado
promoting isolated to scattered showers/storms over the higher
terrain. A few showers/storms could develop in the plains, but with
the lack of moisture aloft and instability only isolated activity is
expected at this time. Temperatures across most of the area will
return to the upper 70s. Saturday and Sunday deterministic and
ensemble guidance depicts much drier weather with temperatures in
the lower 80s slightly above normal for this time of year. Monday
and Tuesday deterministic models depict a upper level trough
potentially cooling us back down Tuesday near 70, along with another
chance of showers and storms.


&&

.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.

&&

$$

DISCUSSION...Schnell/20
AVIATION...Hiris

NWS BOU Office Area Forecast Discussion