827
FXUS65 KBOU 211135
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
535 AM MDT Thu May 21 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms this afternoon, turning
  more numerous in the evening for our eastern counties. A few
  strong to severe storms expected in the plains today.

- Lingering showers into Friday, mainly south of I-70. Remaining
  cool.

- Warmer and drier this weekend, with isolated showers possible
  Saturday afternoon.

- Remaining mild next week but with a return of potential
  afternoon showers and thunderstorms.

&&

.DISCUSSION /Through Wednesday/...
Issued at 212 AM MDT Thu May 21 2026

The upper level trough will move eastward towards our area this
afternoon and evening. Ahead of this trough we`ll see strong
upper level support for showers and storms. At the surface, a
Denver cyclone is forecast to develop near the urban corridor.
Breezy southeast surface winds will bring increased moisture into
our eastern counties this afternoon. Showers and storms are
expected to develop near the foothills and I-25 corridor in the
early to mid afternoon, progressing eastward into the early
evening. Coverage will start out spotty, with increasing coverage
and intensity as the activity moves into the eastern plains. Mid
level lapse rates around 8 C/km and 0-6 km shear values around 40
to 60kts will lead to the potential for supercells today. With
those two parameters in place, the main question for today is
instability. The westward progression of those higher dewpoints
and moisture as well as the splotchy cloud cover this morning will
have a large impact on instability for our area. Right now, it
looks like the highest chance for severe weather will be along and
east of the boundary between moist and drier air masses, which is
still relatively uncertain, but will probably set up just to the
east of the urban corridor. The environment today will support
the development of large hail along with strong gusts. And with
models showing pockets of 0-1km SRH above 100 to 200 m2/s2 we
can`t rules out an isolated tornado as well.

A cold front is forecast to enter our northern counties around 6PM
(give or take an hour), then progress southeast through our forecast
area. Strong surface convergence along the front will act as a
trigger for convection, leading to a mainly filled in line of storms
moving across our eastern counties in the evening. This will be the
best chance for more widespread rainfall. The severe threat
during this time will be lower due to decreased instability in the
evening, but the shear and lapse rates will remain, so we can`t
rule out some strong activity with this line in the evening as
well.

On Friday, temperatures will be cooler for most of the area behind
the front. A shortwave in the flow aloft along with upslope flow
will allow for some showers Friday afternoon. The airmass behind
the front will be more stable limiting the intensity of any storms
on Friday. This highest chance for rain on Friday, will be south
of I-70.

Upper level ridging will start to build over the area this weekend,
leading to a warming trend and decrease in rain chances. There is
still a chance for some isolated showers on Saturday, thanks to
some weak upslope, but coverage should remain low. The ridge will
start to push off to the east Monday into Tuesday as an upper
level trough digs into the western United States. This trough will
bring back rain chances for the early to middle part of next
week.

&&

.AVIATION /12Z TAFS through 12Z Friday/...
Issued at 419 AM MDT Thu May 21 2026

Our TAF sites this morning are VFR. There is an IFR/LIFR stratus
deck to the south and east of our terminals, but the low clouds
should stay out of the TAF sites. Winds through the morning will
be out of the south around 11kts or light and variable. Precip
chances and winds speeds will start to increase around 20Z. Rain
chances don`t look super great, with most of the models keeping
the rain to the east of our TAF sites. But, there is still a
chance for some rain this afternoon, so we left in the prob30.
Along with the rain, we could also see variable gusty winds with
any activity that develops this afternoon. This activity should
move out by 02Z. KDEN will have a second chance of rain this
evening as a cold front moves through the area, triggering
showers and thunderstorms. Right now, models keep the storms just
to the east of KDEN, but there is still a low chance that storms
could develop further west near DIA. Winds will be gusty along and
behind the front, with gusts around 25kt to 30kts from the north.
Winds will decrease around 07Z to 08Z, leaving N/NE winds around
11kts. Ceilings will start to drop again tonight. We currently
have CIGs remaining above MVFR thresholds, but there is a low
chance (~30%) that ceilings could drop closer to 2000ft for a
couple of hours overnight at the TAF sites.

&&

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

&&

$$

DISCUSSION...AP
AVIATION...AP

NWS BOU Office Area Forecast Discussion