638
FXUS65 KBOU 111136
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
536 AM MDT Tue Aug 11 2026

.KEY MESSAGES...

- Hot temperatures to continue this afternoon, then start to cool
  tomorrow and fall below normal Thursday.

- Another round of high-based virga showers this afternoon. Wind
  gusts of30-40 mph are possible from the showers.

- Monsoon moisture becomes plentiful beginning Wednesday afternoon
  bringing daily rounds of showers and thunderstorms through the
  rest week and weekend. Locally heavy rainfall and flash flooding
  may occur.

&&

.DISCUSSION /Through Monday/...
Issued at 417 AM MDT Tue Aug 11 2026

The upper-level high previously centered over the Four Corners has
begun to dissolve, and as such, flow aloft will remain zonal and
weak today, continuing to allow a bit of monsoonal moisture to seep
into the Desert Southwest and parts of Colorado. The better
afternoon shower coverage will reside over the high terrain.
However, with model soundings over the Denver metro and eastern CO
plains showing inverted-V soundings and DCAPE values ~1200 J/kg,
virga showers will still be able to produce strong outflow winds
up to 40 mph even with little precipitation reaching the surface.
We expect afternoon highs to reach the mid 90s over the Denver
metro, with a few 100s possible over the eastern Colorado plains.
If increasing moisture over the region Tuesday evening is able to
keep clouds around through most of the night, morning lows on
Wednesday may only reach the mid 60s across the low elevations.

Monsoonal moisture transport ramps up on Wednesday as the upper
level ridge redevelops to our east with the accompanying high
centered over the southern U.S. plains. This pattern change will
moderate afternoon highs to near-normal on Wednesday, and much
cooler than normal Thursday through Saturday (low 80s across the low
elevations). Additionally, an upper level trough will begin to take
shape just off the coast of California. From a synoptic standpoint,
the combination of the trough off the Pacific coast and the ridge
over the south-central Plains will help channel Pacific moisture
into the Four Corners and provide a classic monsoonal setup.
Shower coverage will become widespread on Wednesday starting over
western Colorado in the late morning and spreading over the Front
Range, foothills, and eventually the Denver metro and eastern
Colorado as the day progresses. Locally heavy rainfall may also
occur with the strongest showers and storms. Precipitable water
(PW) values on Wednesday will rise to around the 90th percentile
of climatology (0.97"). However, shallow warm cloud layers and
storm motion vectors ~20KT will limit flash flooding potential.

Moisture is projected to peak on Thursday afternoon as mid level
Pacific moisture and low level Gulf moisture give way to PW values
that are 150%-200% of the climatological average (~1.4"). From a
flash flood mesoanalysis perspective, a relatively deep warm
cloud layer (~5,000 ft), slower storm motions (LCL-EL mean wind
~15KT), and a long-skinny CAPE profile will lead to conditions
that are favorable the production of efficient rainfall. If this
forecast trend continues, flood watches for flash flooding
concerns may need to be issued in the next 48 hours, once the
footprint of the heaviest precipitation becomes more clear.
Additionally, if the rainfall on Wednesday overperforms, areas
with increased soil moisture may be more prone to flash flooding
on Thursday.

For Friday, PW values will still greatly exceed the 90th percentile
of climatology and a shortwave trough may provide additional forcing
for showers and storms. Faster storm motions will limit flash
flooding potential unless heavy rainfall occurs over areas with near-
saturated soils from the previous day`s rain. Long-range model
ensemble members suggest a slight decrease in moisture for the
weekend, although most solutions still show PWs in the 1.0-1.2"
range due to continued southwest flow aloft.

We are fairly confident that there will be daily chances for
precipitation each afternoon through at least early next week.
Ensemble spread does suggest uncertainty entering the picture
halfway through next week, although near-average monsoonal
moisture still favors afternoon showers over the high terrain on
most days. A warming temperature trend will begin on Monday, with
90-degree afternoon highs over the Denver metro becoming likely
late next week.

&&

.AVIATION /06Z TAFS through 06Z Wednesday/...
Issued at 536 AM MDT Tue Aug 11 2026

VFR to continue through tonight. Smoke could still be an issue,
though the hi-res modelshint at continued improvements. Typical
diurnal wind pattern is expected through mid afternoon (prior to
convection). South-southwest winds will weaken and turn
clockwise, 14-16Z and then become a northerly direction 17-18Z.
Anotherround of afternoon and early evening scattered showers and
isolated thunderstorms will occur. The best time frameat the
Denver airports looks to be 20-24Z. Wind gusts up to 35 knots are
possible, and one or two wind shifts will likely occur. The
threat for showers and thunderstorms decreases 00-03Z, and winds
are expected to return to the south to southwest for the night.

&&

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

&&

$$

DISCUSSION...AA
AVIATION...BM

NWS BOU Office Area Forecast Discussion