580
FXUS65 KBOU 231137
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
537 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 /12Z TAFS through 12Z Thursday/...
Issued at 535 AM MDT Wed Sep 23 2026

Winds have been drainage, but elevated through much of the
overnight. Over the last hour, winds have started to become rather
light. Winds will turn to southeast by the early afternoon with
lowering ceilings as the afternoon progresses and moisture
continuing to increase.

Rain chances are fairly uncertain this evening and overnight with
changes possible in upcoming TAFs. The latest CAMs have
significantly backed off on rainfall chances tonight, especially
for KDEN. Nevertheless, showers are possible as early as 20z at
all three sites. Nearly every short-term model keeps only low
(~20%) rain chances this evening, except for at KBJC. Another push
of monsoonal moisture is now expected early Thursday morning
(9z-12z). KAPA will likely see the bulk of the activity and thus
could have lowered visibility/ceilings. KDEN has a lower chance
for showers, so have kept a prob30 there. BKN/OVC ceilings as low
as 4,000 ft AGL at KAPA and 5,000 ft AGL at KDEN are in play,
particularly after 9z Thursday, along with lowered visiblities at
times.

Regardless, we are confident of at least bkn070 ceilings from
Wednesday evening onwards at all three sites. The prob30 and tempo
groups will continue to be refined as we close in on this period.

&&

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

&&

$$

DISCUSSION...AA
AVIATION...MV

NWS BOU Office Area Forecast Discussion