900
FXUS65 KBOU 210601
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1201 AM MDT Thu May 21 2026

.KEY MESSAGES...

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

- 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 1225 PM MDT Wed May 20 2026

Our ongoing pattern of unsettled weather continues marching along.
Additional beneficial precipitation was observed last night and
into this morning aided by upslope flow and jet-induced lift, with
bands focused south of I-70 for the most part, and the higher
elevations of Park County receiving over 6" of new snow. The
responsible shortwave will lift northeast through the remainder of
the day, merging with the broader synoptic flow but maintaining
modest lift over the plains this afternoon. We`re beginning to see
some redevelopment of showers across the high country associated
with the passing shortwave, and these will gradually spread into
the lower elevations through the afternoon. As of this writing
(~12 PM Wed), ACARS soundings from Denver International Airport
still snow a capped environment near the 700mb level, hindering
shower development. However, this should erode in the coming
hours and allow for more expansive coverage across the urban
corridor and plains with a few embedded thunderstorms. Instability
is quite marginal today and generally peaking at under 400 J/Kg
for most locations, so severe thunderstorms are not anticipated.
Activity looks to exit our eastern plains late this evening.

On Thursday, a second shortwave will develop over western Wyoming,
traversing our area overnight. Ahead of it, a moderately moist
airmass will remain as a well-defined Denver cyclone sustains
south and southeast flow over the plains, with some warm advection
in place as well. Low-level lapse rates look to steepen notably,
promoting higher ML CAPE values over 800 J/Kg by mid-afternoon,
mainly east of I-25. Bulk shear locally in excess of 50-60 kts
would support development of a few discrete supercells late
afternoon and into the evening for the plains, with much of the
convective activity likely initiating/intensifying with the
convergence boundary associated with the Denver cyclone mid-
afternoon. Large hail will be the primary threat from any strong
to severe storms, with a lesser but nonzero potential for strong
outflows and a few landspouts. Thunderstorm activity will linger
later into the evening than is typical, fueled by the passage of
the trough axis, and waning more noticeably behind the front after
midnight. In the eastern plains, a few locations may pick up 1-2"
of rain with the heaviest cells, especially given the potential
for successive storms.

Slightly cooler temperatures can be expected for Friday following
the nocturnal front, with highs generally around 10 degrees below
average. This also implies a more stable environment, with limited
opportunity for thunderstorm development. Nonetheless,
northeasterly upslope flow will still allow for some afternoon
showers and perhaps an isolated storm or two primarily over the
southern foothills and Palmer Divide. Precipitation chances will
be much lower elsewhere.

A warming trend returns for the weekend, and we may be scraping
the 80`s for the lower elevations come Sunday. With a third weak
shortwave in the mix on Saturday and some marginal instability in
place, some isolated afternoon showers and weak thunderstorms will
be possible (20-50% chance, highest for the Palmer Divide). Not
so much the case for Sunday, when most if not all areas look to
stay dry. Opportunities for more afternoon convection will return
next week as a troughing pattern becomes more established to our
west.

&&

.AVIATION /06Z TAFS through 06Z Friday/...
Issued at 1147 PM MDT Wed May 20 2026

A few isolated showers remain near KAPA this evening, with rain
continuing on and off for the next hour or so for Centennial.
CIGs are expected to remain VFR overnight, with ceilings
generally staying above 6000ft, dropping to around 4000ft at KBJC
and KAPA in the morning before lifting again for the late morning.
Showers and storms will begin to develop around 20Z. Coverage
will be a bit more sparse around the airports this afternoon, so
we`ve gone for a prob30 rather than a tempo for rain chances.
Coverage of storms will be significantly higher to the east of
the airports, especially as the cold front moves through in the
late evening. Storms along the front could start to approach the
eastern side of DIA, so we`ve gone with another prob30 to account
for that chance. Winds behind the front will be gusty around 22kt
to 25kts from the north.

&&

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

&&

$$

DISCUSSION...BRQ
AVIATION...AP

NWS BOU Office Area Forecast Discussion