793
FXUS65 KBOU 230611
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1211 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, partcicularly 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 /06Z TAFS through 06Z Thursday/...
Issued at 1205 AM MDT Wed Sep 23 2026

A pretty busy TAF over the next 24-36 hours....Showers and some
gusty winds have come off the foothills over the last 90 minutes.
Some gusts to around 25 kts remain possible at all three sites
through about the next hour. Winds have already turned to drainage
behind this activity and will continue as drainage or a bit more
westerly through this morning. KBJC will remain light and
variable after these showers pass through.

Winds will turn to southeast by the early afternoon with lowering
ceilings as the afternoon progresses and moisture continuing to
increase. The latest CAMs have pushed up the timing for the onset
of showers. Showers are possible as early as 19-21z at all three
sites and then become increasingly likely for much of Wednesday
evening and overnight into Thursday morning. Generally, Wednesday
early evening (~0z to 6z Thursday) appears to be the timing of
the heaviest rainfall through this period at KAPA and KDEN and
have covered this with tempo groups. KBJC has a lower chance for
showers, so have kept a prob30 there.

KAPA will likely see the bulk of the activity and thus could have
even further lowered visibility/ceilings than the other two
sites. BKN/OVC ceilings as low as 4,000 ft AGL at KAPA and 5,000
ft AGL at KDEN and KBJC are in play, particularly after 0z
Thursday along with lowered visiblities at times. Regardless, we
are increasingly confident of at least bkn070 ceilings from
Wednesday evening onwards at all three sites.

Showers will continue across the area (in the vicinity of all
three sites) through the overnight with the latest CAMs hinting
at more steady and widespread rainfall at/near KAPA past 6z
Thursday. The prob30 and tempo groups will continue to be refined
as we approach this period.

&&

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

&&

$$

DISCUSSION...AA
AVIATION...MV

NWS BOU Office Area Forecast Discussion