166
FXUS65 KBOU 210009
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
609 PM MDT Thu Aug 20 2026

.KEY MESSAGES...

- Isolated showers and storms in the mountains mainly south of
  I-70 ending this evening.

- Hot Friday with high temperatures pushing 100F over portions of
  the plains and I-25 Corridor. High based late afternoon and
  evening showers/storm/virga producing gusty microburst winds.

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

&&

.DISCUSSION /Through Thursday/...
Issued at 133 PM MDT Thu Aug 20 2026

A warmer and drier airmass is taking hold today as the ridge
starts to amplify over the Four Corners into the Great Basin. We
still have enough moisture per current satellite imagery for a few
showers and weaker storms in the mountains, mainly south of I-70.
Those will end early this evening as the airmass stabilizes,
while the plains will remain too dry and stable for any convective
activity. Overnight lows will be several degrees above normal.

On Friday, we`ll be back to the frying pan as the thermal ridge
shifts eastward and centers itself across Colorado. 700 mb
temperatures warm a couple more degrees C, which supports highs in
the mid to upper 90s across the plains and I-25 Corridor, with a
few spots nearing 100F from downtown Denver to Greeley and Fort
Collins. The record for tomorrow in Denver is 99F set in 2023,
and we should be very close to that at the official reporting
station. Those readings also bring us very close to Heat Advisory
criteria, but most locales should stay just below 100F. There will
be some heat relief in the form of high based convective clouds
late in the day as mid/upper level moisture starts to spread into
the region. Given large DCAPE of 1500-1700 J/kg and deep
inverted-v profiles, strong microburst winds to 50+ mph will be
possible from any high based showers.

For the weekend, ensembles are still showing the upper level ridge
axis to shift slowly eastward or flatten, with the flow aloft
trending more westerly. This will allow for an uptick in monsoonal
moisture across the forecast area, leading to scattered thunderstorms
each afternoon. In these moisture and flow patterns, the most
numerous storms are expected over the mountains and eastern
plains. Meanwhile, the majority of the storms along the I-25
Corridor will be higher based as the airmass is still quite warm
and low level moisture is expected to be lacking. But given the
uptick in precipitable water to near 150% of normal, that still
doesn`t mean we can`t see locally heavy rainfall.

There may be some change in this pattern as flow turns slightly
more west-northwesterly toward Tuesday or Wednesday. That could
allow for a weak backdoor front or two with increasing low level
moisture, but plenty of uncertainty exists here with respect to
timing and intensity of any surge(s). In any case, it appears
temperatures will settle a little closer to (still above) normal
for this weekend through much of next week. And enough moisture
will be around to keep a chance of storms in the forecast most
days.

&&

.AVIATION /00Z TAFS through 00Z Saturday/...
Issued at 605 PM MDT Thu Aug 20 2026

Current observations show winds are easterly across the area with a
few lingering gusts up to 20KT driven by diurnal heating. Winds will
continue to turn clockwise, becoming southeasterly by around 01-02Z
before drainage S/SSW winds take over in the late overnight hours.
There is a small chance that an outflow tracking over eastern
Nebraska could survive for long enough to make it to the CO plains
in the early morning hours (07Z-10Z). If the boundary makes it to
the Denver area, it would reinforce (10-15KT) the southerly
drainage winds already in place at that time.

For tomorrow, winds will start out SW and become more north to
northeast by the late morning. The biggest concern will be dry
microbursts and strong erratic outflow winds, up to 45KT. High-
based showers will start developing over the foothills at around
19Z, likely becoming scattered over the Denver metro by 22Z. No
precipitation is expected to reach the surface.

&&

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

&&

$$

DISCUSSION...20
AVIATION...AA

NWS BOU Office Area Forecast Discussion