050
FXUS65 KBOU 041732
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1132 AM MDT Thu Sep 4 2025

.KEY MESSAGES...

- Isolated showers and weak thunderstorms late this afternoon and
  evening.

- Near critical fire weather conditions are expected across the
  plains on Thursday due to warm, dry, and breezy weather.

- Better coverage of storms and above normal temperatures expected
  this weekend, mainly over the higher terrain.

&&

.DISCUSSION /Through Wednesday/...
Issued at 142 PM MDT Wed Sep 3 2025

Current surface observations show widespread wind gusts up to 35
mph across the plains as a dry cold front moved through the area
earlier this afternoon. Satellite imagery has a cumulus field
building over the higher terrain, but most of the forecast area
should remain dry this afternoon/evening as we are under
subsident flow. The only exception would be the foothills, where
upslope flow and steep lapse rates of ~9 dg C/Km would allow weak
high- based showers/storms to develop this afternoon. With a
strong temperature inversion this morning inhibiting instability
building over the area, and SPC mesoanalysis having less than 500
J/kg of SBCAPE across the high terrain and plains for the rest of
the day, the severe threat is low (<10% chance). However, modeled
Skew-T soundings show DCAPE values ~1200 J/kg, which would support
gusty outflow winds up to 40 mph.

On Thursday, a strong upper level shortwave trough will move
across the Dakotas. With the incoming trough, flow aloft in
Colorado will initially turn westerly/northwesterly, which will
aid in adiabatic warming from downsloping winds. Temperatures will
be in the high 80s across the plains, with some places reaching
the low 90s. With wind gusts up to 30 mph and relative humidity
values around 15-20%, localized elevated fire weather conditions
are possible in the afternoon, particularly the northern plains. By
the late afternoon/evening, a cold front is progged to push
across our forecast area. Some hi- res models indicate wildfire
smoke being advected into our region behind the front,
particularly in the northern plains. However, scattered showers
associated with the cold front could help clear out the smoke.
With steep lapse rates and DCAPE values expected to be >1000 J/kg,
the main threat will be wind gusts up to 45 mph with the
strongest storms.

Friday will be the coolest day of the forecast period as
temperatures are expected to be in the low 70s. An upper level
ridge will build over the western United States. However, we will
enter an active pattern through the weekend due to multiple
embedded shortwaves within the ridge. Along with the forcing,
moisture will be advected into the region due to a tropical system
in the Pacific. There are inconsistencies in the track of the low,
with the ECMWF indicating a more southerly track while the GFS has
been trending towards a more northerly track. For this reason, the
exact coverage of showers/storms is still uncertain. Most likely,
we will have daily afternoon convection across the higher terrain
that could spill onto the adjacent plains.

Looking forward into next week, ensemble models are in agreement
of slightly above normal temperatures across the forecast area,
with some model runs indicating the possibility of highs in the
low 90s.

&&

.AVIATION /12Z TAFS through 12Z Friday/...
Issued at 1132 AM MDT Thu Sep 4 2025

North to northeast winds will continue through this afternoon and
evening. A cold front will increase northeast winds with gusts to
30 knots 01-02Z. VFR through tonight, though increasing smoke may
create slant visibility issues. A significant smoke layer aloft
is expected to accompany the cold front over northeast Colorado
and produce slant visibility issues and possibly reduce surface
visibility to 5SM. Isolated showers and thunderstorms are also
expected this late this afternoon and evening, after 21Z. Main
impact with the showers and storms will be outflow winds, which
may bring a wind shift or two to the Denver airports.

&&

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

&&

$$

DISCUSSION...Ideker
AVIATION...Meier