613
FXUS65 KBOU 232101
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
301 PM MDT Wed Sep 23 2026

.KEY MESSAGES...

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

- Friday another disturbance is likely to move through bringing
  more chances for showers/storms.

- Drier and warmer this weekend before an upper level trough
  brings cooler temperatures and potentially our next chances for
  showers/storms early next week.

&&

.DISCUSSION /Through Wednesday/...
Issued at 253 PM MDT Wed Sep 23 2026

Current analysis shows the moist airmass from AZ/NM has infiltrated
our area. PWATs sit at 0.8-0.9 in the foothills and Denver metro.
Towards the eastern plains they increase to 1.0-1.3. Current radar
depicts showers developing in the plains where some peaks of
sunshine still remain. The next 36 hours or so of the forecast
remain highly uncertain in regards to placement and development of
convective activity.

Model guidance displays a wide range of solutions, and combined with
the cloud shield across the forecast area we are concerned this will
limit instability significantly thus lowering the chances for
shower development. Current ACARS DEN sounding also indicates we
are capped, but with abundant moisture aloft. Furthermore, the
shortwave that was advertised to move through has shifted to far
Southeastern Colorado towards the Kansas border limiting
widespread chances for our forecast area. Even with the lack of
true lift, the amount of moisture present should be enough to
produce showers for most of the area. Here is a breakdown of the
chances. The eastern and southern plains will see the greatest
rainfall from this system ~60-70% through around Thursday
afternoon, and the urban corridor and Denver metro will see about
a 40-60% chance. South Parks chances will increase to ~60-80%
through Thursday evening. Some model guidance depicts drier air
filtering in from the northwest so the Northern Mountains could
see more limited activity, especially tonight.

Thursday morning model guidance has convection shifting off to the
south and east of our area, but as the afternoon approaches we
should see another increase in shower activity in the higher terrain
around noon (~60%), and urban corridor/Denver Metro later in the
afternoon (~40-50%). Some CAMs depict a round of scattered to
widespread storms moving pushing through the urban corridor to
eastern plains in the evening while short term guidance like the
NAMNEST and HRRR isn`t exactly on board with this. It is also
worth it to note storm motion for today and Thursday is between
5-15kts and the 12,18Z runs of the HRRR indicate a storm that
trains over the Cameron Peak burn scar area for a few hours. This
is only one solution, but the potential for slow moving storms
with localized flash flooding will be possible through Thursday
evening. If enough cloud cover clears Thursday night we could see
the potential for patchy fog to develop mostly in the plains and
mountain valleys.

Friday most model guidance depicts a shortwave move into our
forecast area bringing shower/storm potential. PWATs are still
expected to be 170-190% above normal and forecast soundings indicate
CAPE will increase with limited CIN. The GFS is an outlier currently
and has the precipitation occurring further south of our area.
Temperatures will warm back up to mid/upper 70s.

Saturday and Sunday still trends drier and warmer up to the low/mid
80s in the urban corridor with 60s in the higher terrain. Monday and
Tuesday temperatures cool down due to the passage of an upper
level trough potentially bringing our next best chance for
precipitation.

&&

.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...Schnell
AVIATION...Hiris

NWS BOU Office Area Forecast Discussion