903
FXUS65 KBOU 211903
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
103 PM MDT Thu May 21 2026

.KEY MESSAGES...

- Strong to locally severe thunderstorms expected late this
  afternoon through this evening in the plains, mainly east of
  I-25.

- Elsewhere, weaker isolated to scattered showers/t-storms can be
  expected with and behind an early evening cold front.

- 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 Thursday/...
Issued at 1218 PM MDT Thu May 21 2026

Ingredients are coming together as anticipated to provide for an
active afternoon and evening for our plains in particular. Cloud
cover has reduced considerably across the urban corridor and will
continue to thin over the plains in the coming hours, helping to
destabilize the environment. Surface moisture remains a potential
limiting factor for portions of the I-25 corridor with dewpoints
falling below 40F this afternoon, capping MLCAPE below ~400 J/Kg
at most.

Thunderstorms remain on track to develop mid-afternoon, mainly
after 3-4pm, favoring initiation east of I-25 and off the Palmer
Divide, where a DCVZ will become increasingly pronounced as the
afternoon progresses. These will spread into a much more unstable
environment in the eastern plains where an axis of more favorable
low-level moisture (dewpoints exceeding 50F) is present, roughly
to the east of the north/south line from Fort Morgan to Agate.
Ample bulk shear of 45-60 kts should support sustained growth of a
few supercells into Lincoln/Washington/Logan Counties late
afternoon into early evening, capable of producing large hail to
~2" in diameter with the strongest storms, as well as isolated
strong wind gusts and/or a weak tornado.

For the urban corridor, the highest chances for showers and
thunderstorms will arrive in the evening as a cold front descends
south between 5-8pm, although any convection should be sub-severe.
However, the front will provide an opportunity for redevelopment
of strong thunderstorms into the plains, reinforced by a secondary
frontal surge mid/late evening associated with the upper level
trough axis. With time, convection should become less discrete in
nature, favoring some upscale growth into a broader area of
thunderstorms across the northeast plains, exiting into KS/NE
roughly after midnight. Post-frontal winds will remain robust
overnight across our plains with gusts 25-40 mph.

This evening`s front will usher in cooler temperatures for Friday,
along with a more stable airmass that will significantly reduce
precipitation potential for most areas. Nonetheless, some pockets
of marginal instability could remain south of I-70, and upslope
flow combined with the passage of another (weaker) shortwave aloft
will promote some showers and potentially a few weak thunderstorms
in the late afternoon and evening, focused across the Palmer
Divide.

We`ll trend noticeably warmer Saturday into Sunday, with the
latter seeing highs climb into the lower 80`s for the plains and
urban corridor. Some lingering mid-level moisture and yet another
weak shortwave may support isolated and weak high-based convection
on Saturday, although most will stay dry, and that will certainly
be the case on Sunday as higher pressure settles in. A more
unsettled pattern looks to return as early as Monday with renewed
potential for diurnal showers and thunderstorms through much of
the week.

&&

.AVIATION /18Z TAFS through 18Z Friday/...
Issued at 1151 AM MDT Thu May 21 2026

VFR conditions expected through the TAF period. Winds are
currently light and VRB at all TAF sites and will continue for the
next hour or two. By 20Z, winds should become more easterly
(easterly to southeasterly and DEN) around 10-15 kts.
Precipitation chances increases at this time, however convection
should be isolated-to-scattered through 00Z and may not impact the
airports besides gusty outflows. For this reason, have decided to
keep the PROB30 for all terminals. Between 00Z and 05Z convection
should increase with the arrival of the cold front, however
the bulk of the precipitation looks to stay east of the airports.
Have decided to keep the PROB30 in the TAF instead of TEMPO due to
this uncertainty. However, gusty VRB outflow winds are still
possible.

With the arrival of the cold front (around 01Z/02Z), expect
northerly winds gusting up to 30 kts, before gradually weakening
and turning more easterly by 05Z and through the morning. There is
a low chance (

NWS BOU Office Area Forecast Discussion