547
FXUS65 KBOU 230039
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
639 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 /00Z TAFS through 00Z Thursday/...
Issued at 638 PM MDT Tue Sep 22 2026

Scattered storms and showers have been popping up off the Palmer
Divide and lingering in the vicinity of KAPA, producing heavy rain
and lowering cloud ceilings as low as 5000ft. Given the lack of
instability in the latest ACARS soundings and current radar
observations show storms weakening as they move northward, we expect
these storms to weaken as they approach KDEN; however, they could
still drop cigs to ~6000ft and reduce visibility over the airfield
as they pass. Additionally, storms approaching now are producing
gusts up to 35kts. After storms pass, winds are expected to be
variable and mainly outflow-driven until showers clear the area,
which is expected to be around 03Z.

Winds should then turn south overnight and become light and variable
in the early morning, around 12Z. Clouds are expected to linger
overnight, but ceilings should remain high enough for VFR to
prevail. Tomorrow afternoon/evening brings with it another chance
for scattered showers/storms. Current model guidance suggests most
precipitation will occur after 00Z, though we could see some showers
pop up starting around 22Z. There`s still some uncertainty on this
timing and we`ll be updating the current PROB30 and TEMPO groups
accordingly once we get a better idea of what tomorrow`s instability
and moisture will be. Outside of any variability from storms, winds
should be predominantly easterly throughout the afternoon and
evening.


&&

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

&&

$$

DISCUSSION...Schnell/20
AVIATION...AGS