852
FXUS65 KBOU 201902
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
102 PM MDT Wed May 20 2026

.KEY MESSAGES...

- Unsettled through Thursday, with 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 /18Z TAFS through 18Z Thursday/...
Issued at 1210 PM MDT Wed May 20 2026

Current observations show a Denver cyclone set up just to the
west of KDEN. This cyclone is expected to shift southward over the
next few hours leading to N/NNE winds by early this afternoon at
all three sites. Current radar shows showers ongoing to the west
of KBJC in the mountains. There is still strong agreement that
showers and storms should move in from west to east affecting all
three terminals this afternoon starting as early as 19z and
lasting into the early evening. Visibility could lower to MVFR or
IFR at times as this rainfall moves through.

Otherwise, winds will shift around to drainage by this evening at
all three TAF sites. Low clouds are expected to continue
overnight given the presence of deep low- to mid-level moisture.

For tomorrow, a Denver cyclone is forecast to setup near/over
KDEN once again. The evolution of this feature will in turn affect
the SHRA/TSRA chances. For now, we expect showers and storms in
the vicinity of the terminals by around 19z to 21z. These showers
and storms should last well into the evening. We have left out any
mention of -TSRA for now, but there is a chance (15-20%) given
the decent instability expected. Visibility could once again lower
to MVFR or IFR at times as this rainfall moves through. There is
also the possibility of some breaks in the clouds, especially in
the afternoon tomorrow at KDEN, so have raised ceilings to around
12,000 ft AGL for now. Finally, gusty winds are possible tomorrow
afternoon with any storms that do move near the three sites.

&&

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

&&

$$

DISCUSSION...BRQ
AVIATION...MV

NWS BOU Office Area Forecast Discussion