735
FXUS65 KBOU 231737
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1137 AM MDT Wed Sep 23 2026

.KEY MESSAGES...

- 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.

- Cooler weather returns next week.

&&

.DISCUSSION /Through Tuesday/...
Issued at 1210 AM MDT Wed Sep 23 2026

Current radar imagery shows a few sprinkles lingering over the
Denver metro at this time, with patchy low clouds visible on
satellite. This evening was quite active as storms that formed
over the southern Front Range and Palmer Divide became clusters of
heavy rainfall, leading to the issuance of a Flood Advisory and
one Flash Flood Warning. This goes to show that the ingredients
necessary for efficient rainfall production are already present in
our atmosphere, and they will remain present through Thursday
night, hence the high PoPs over the next 48 hours. However, the
tricky part about this forecast will be pinning down when the best
instability or forcing will materialize and therefore, the
heaviest rainfall rates.

Moisture continues to increase Wednesday afternoon and we expect
shower coverage to become more widespread. Convection will likely
begin over the mountains first at around 12PM-1PM, while the Denver
metro and east Colorado plains would start to see a better chance
for downpours by mid afternoon. The best window for heavy rainfall
over the Denver metro looks to be between 4PM and 8PM Wednesday
evening while instability is at its highest (~500 J/kg CAPE). The
east Colorado plains may see the peak of rainfall activity occur
later in the evening as the upper level disturbance and vorticity
maxima push eastwards. Slow storm motion vectors (10-15 mph) and
training may lead to continued rainfall over the same location, and
at least a localized flash flooding threat. Areas that have already
received rainfall from storms the last couple of days (mainly the
Palmer Divide) will be more vulnerable to flooding given increased
soil moisture already in place.

The nature of the showers will become more stratiform-like after
10PM Wednesday night, with scattered showers continuing through most
of the day on Thursday given such anomalous moisture present (1.0-
1.4" PWATS). Thick low level clouds will limit instability and keep
afternoon temperatures at low elevations 10-15 degrees below normal,
with some areas only reaching the mid 60s. Shower chances decrease
Thursday night as flow aloft becomes slightly more zonal and the
disturbance completely moves off into the Great Plains. If high
clouds are able to clear Thursday night, leftover moisture is likely
to lead to the development of some areas of fog, particularly
over the plains. Additional showers will be possible with a
shortwave Friday afternoon, mainly over the high terrain.

Saturday and Sunday look to be dry and warmer, with afternoon
temperatures warming back up to the low 80s for the Denver metro.
Models are trending cooler for next week due to the passage of an
upper level trough sometime between Monday-Tuesday.

&&

.AVIATION /18Z TAFS through 18Z Thursday/...
Issued at 1131 AM MDT Wed Sep 23 2026

Rather low confidence through the TAF period.

Winds are very light at the terminals, but are still expected to
gradually turn towards the southeast this afternoon. Speeds should
remain fairly light through the day. Weak convection is expected
to develop over the next few hours, though given little/no
instability, most of the activity near the metro should be SHRA vs
TSRA.

From this evening and beyond, there`s essentially no obvious model
signal to work with. Some showers may linger a bit beyond the
current PROB30, with another surge of moisture attempting to push
towards APA by 09z. A few models develop steady rain and some MVFR
cigs up to about I-70, while several CAMs are completely dry and
maintain VFR all of Thursday morning. I did not see a reason to
deviate much from the previous TAF with generally a BKN040-060
expected for a few hours in the morning.

There is slightly better agreement that winds will eventually turn
to the north or northeast by late Thursday morning, which would
then continue into the afternoon and evening hours. Though there
is poor agreement in this period, some models develop deep/moist
upslope... leading to another potential period of MVFR cigs/visby
with rain showers late tomorrow afternoon. Have introduced another
PROB30 at DEN to end the TAF period... and will hope for better
model agreement sometime soon.

&&

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

&&

$$

DISCUSSION...AA
AVIATION...Hiris

NWS BOU Office Area Forecast Discussion