429
FXUS65 KBOU 220013
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
613 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 /00Z TAFS through 00Z Saturday/...
Issued at 557 PM MDT Thu May 21 2026

Cold front is making its way through all terminals currently, with
gusts up to 30-35 kts behind it. Expect lighter northerly winds
by 01Z/02Z, however gusts up to 25 kts are still likely. A
secondary frontal push will occur by 04/05Z which will bring
another round of gusty winds up to 30 kts. Showers and
thunderstorms have increased in coverage with the arrival of the
cold front, however most of the convection has remained east of
the airports. Will keep the PROB30 in to account for isolated
showers/thunderstorms through this evening. Most likely chance for
the next round of precipitation will be with the arrival of the
secondary front.

Winds overnight should begin weakening by 08Z-10Z, remaining
generally north/northeast. Expect typical diurnal pattern in the
afternoon, with winds shifting to the southeast briefly before
returning to drainage. Evening showers are possible tomorrow,
however convection should remain south of the airport.

&&

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

&&

$$

DISCUSSION...BRQ
AVIATION...MAI

NWS BOU Office Area Forecast Discussion