399
FXUS65 KBOU 111132
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
532 AM MDT Fri Sep 11 2026

.KEY MESSAGES...

- Very warm today with only isolated high based showers/virga
  late this afternoon and evening.

- Slight increase in shower/storm coverage this weekend. Cooler
  Saturday, then warmer Sunday.

- Unsettled pattern next week, with multiple cold fronts expected
  to bring a few more noticeable cooldowns.

&&

.DISCUSSION /Through Thursday/...
Issued at 231 AM MDT Fri Sep 11 2026

Zonal flow aloft will strengthen today, bringing a stronger
downslope component and thus a bit more warming. We expect highs
to reach 90F or more over most of the plains and I-25 Corridor.
To offset that, there is some mid/upper level moisture evident on
satellite and radar now reaching northern Utah. This will continue
to push east today, resulting in enough for scattered virga,
isolated high based showers, and even a lone weak storm. The main
threat of any light precipitation would be over the northern
mountains this afternoon, spreading to the northern plains this
evening, but even there coverage would be sparse. Any high based
showers/virga would support gusty outflow winds to 40 mph given
increasing environmental flow and DCAPE increasing to 800-1200
J/kg.

For tonight, a cold front pushes south across the High Plains and
through northeast Colorado late tonight into early Saturday
morning. This will lead to cooler temperatures (near normal) for
Saturday. While moisture levels increase slightly, considerable
uncertainty exists for afternoon and evening shower/storm coverage
due to thermal profiles. For the most part, we don`t think we`ll
reach convective temps over the plains but still can`t rule out
a few late day showers and storms spilling eastward from the
higher terrain due to mid level instability and moisture.

Sunday will likely feature a return to much above normal
temperatures. MOS guidance suggest highs pushing into the mid 90s
for metro Denver and the I-25 Urban Corridor. That may be a bit
aggressive as there is some guidance (not surprisingly) slowing
the redevelopment of lee troughing and erosion of low level
moisture. The record for Denver on the 13th is 96F set in 2018,
1990, and 1895, but at this point it appears we`ll most likely
stay a couple degrees shy of that. With regard to convection,
isolated showers and storms will be high based and relatively
weak. However, if a storm or two can break the cap over the
northeast plains they could certainly tap into higher MLCAPE and
become severe.

As discussed yesterday, the cooldown for Monday appears to be
tempered as the next cold front/upper trough has been delayed
slightly. However, there is still high confidence in more
significant cooling for Tuesday behind a moderately strong early
(meteorological) autumn cold front. While daily uncertainties
exist about the degree of cooling, there is modest agreement we`ll
settle into highs in the 70s (and 30-40% chance of 60s) for the
plains and I-25 Corridor. A brief warmup is possible for
Wednesday before yet another front arrives Thursday. Ensembles are
in decent agreement holding a plume of mid/upper level moisture
and higher than normal climatological precipitable water over us.
Thus, we should have daily chances of showers and storms most of
the days this upcoming week.

&&

.AVIATION /12Z TAFS through 12Z Saturday/...
Issued at 532 AM MDT Fri Sep 11 2026

Main concern today is threat of gusty outflow winds from high
based virga/sprinkles 22Z-03Z. Given upstream satellite imagery
and radar returns, we believe there is enough moisture to warrant
at least a chance of gusty outflow winds. DCAPE is expected to
grow to 800-1200 J/kg and environmental winds are also increasing
today. There is uncertainty, however, if we fully reach
convective temperature. For now, we added a PROB30 VRB G30kts to
the TAFs to account for this potential with the main risk 23Z-02Z.

Otherwise, VFR conditions will persist. Light S-SW winds will
become Light and variable toward 16Z. There is still some
uncertainty in prevailing wind direction by 20Z, with a battle
between diurnal upslope and stronger westerlies trying to advance
off the foothills. For now, we`ve kept a N-NE component at KDEN
and KAPA, with a more W-NW wind likely at KBJC. Winds will
eventually settle to more SE-S-SW 02Z-06Z. A weak cool front is
then expected to arrive 10Z-12Z Saturday, which should push winds
to the NW-N-NE through early Saturday morning.

&&

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

&&

$$

DISCUSSION...20
AVIATION...20

NWS BOU Office Area Forecast Discussion