668
FXUS65 KBOU 200613
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1213 AM MDT Thu Aug 20 2026

.KEY MESSAGES...

- Summer heat and drier Thursday into Friday, although isolated
  showers/storms in the mountains.

- Monsoon moisture returns this weekend and holds into early next
  week, with increasing chance of storms.

&&

.DISCUSSION /Through Wednesday/...
Issued at 1242 PM MDT Wed Aug 19 2026

Main concern in the short term is development and strength of
convection this afternoon into early evening. We are seeing drying
in the mid and upper levels spread southward across the forecast
area, but low level moisture is hanging on across the plains. Best
MLCAPE is developing pretty much as expected over the Palmer
Divide through Lincoln County, where MLCAPE has grown to 1000-1500
J/kg. Farther north, the drying will limit overall MLCAPE to just
a few hundred J/kg. Thus, the main threat of any severe weather
would be from the crest of the Palmer Divide through central/
southern Lincoln County through early evening. Farther north,
mainly isolated and less intense storms are expected as there is
still some weak support/instability along and south of the upper
level jet axis.

Convection is expected to end latest over the far southern portion
of our forecast area by mid to late evening, with clearing skies
and temperatures a few degrees above normal overnight.

Thursday and Friday will feature very warm and mostly dry weather
as the upper level ridge starts to amplify and a drier northwest
flow aloft holds over the forecast area. The amplification of the
ridge will support a return of full summer heat, with highs
pushing into the lower to mid 90s across all of the plains and
I-25 Corridor on Thursday. Friday will see even further warming,
with mid to upper 90s well agreed upon by guidance.

Looking into this weekend, ensembles were still in good agreement
that monsoonal moisture arrives as the upper level ridge migrates
ever so slowly eastward. That would put the forecast area in
southwest flow aloft and increased moisture advection. Precipitable
water (PW) values climb to around 150% of normal on average. That
will support scattered to numerous storm coverage in the
mountains each day, at least once the ridge axis shifts slightly
eastward - which should be by Sunday at the latest. That`s when a
shortwave moves over the northern U.S./Canada border area,
leading to a little more westerly component aloft. That component
would also aid an increase in showers/storms drifting eastward
onto the plains.

That same relative weather pattern holds through early next week,
which supports daily chances of showers and storms along with
slightly cooler (but still above normal) temperatures. A couple
weak backdoor fronts are possible during this period, which means
a day or two should see highs settle back into the mid to upper
80s across the plains and I-25 Corridor.

&&

.AVIATION /06Z TAFS through 06Z Friday/...
Issued at 1139 PM MDT Wed Aug 19 2026

VFR to persist through the TAF period. Winds are in the process of
settling into drainage at KDEN/KAPA, with a more northwesterly
flow in place at KBJC. These conditions are expected to persist
for the next few hours before a slightly more SW flow develops by
10Z/11Z at KDEN/KAPA. Winds are expected to begin a clockwise turn
by 15Z before settling into a northeasterly flow by around 18Z,
where they should remain through the afternoon. Prevailing wind
speeds should remain below 10 kts, with a few gusts between 12-15
kts possible in the afternoon. Winds will continue their
clockwise turning again around 0Z, with drainage winds expected
again for the overnight hours. Any afternoon showers or storms
that develop are expected to remain over the higher elevations to
the southwest of the TAF sites.

&&

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

&&

$$

DISCUSSION...20
AVIATION...9

NWS BOU Office Area Forecast Discussion