915
FXUS65 KBOU 230743
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
143 AM MDT Tue Jun 23 2026

.KEY MESSAGES...

- Widespread severe thunderstorm risk for all of the lower
  elevations starting mid-afternoon today, lasting well into the
  evening. Very large hail exceeding 2-3" in diameter will be
  possible with the strongest storms.

- Additional rounds of severe storms expected Wed and Thu for the
  lower elevations, with increasing flash flooding risk.

- Locally critical fire weather conditions in the mountains today
  and Wed. Fire danger increases considerably this weekend, as
  much hotter, drier and winder weather arrives.

&&

.DISCUSSION /Through Monday/...
Issued at 121 AM MDT Tue Jun 23 2026

Ingredients continue coming together for a significant severe
weather threat later today lasting well into the evening, so let`s
dive in...

Strengthening lee cyclogenesis is evident in the surface
wind/dewpoint fields early this morning, with an axis of robust
S/SE winds across our central and southern plains. This
intensification of the surface low east of the southern Rockies
will persist through the day, sustaining 50 to 60 degree dewpoints
east of the I-25 corridor and promoting a moderately to highly
unstable environment for the lower elevations, with MLCAPE values
locally in excess of 2,000-3,000 J/Kg, coincident with the passage
of several subtle shortwaves at mid-levels which should drive
multiple rounds of convection across the region. Activity will be
slower to develop today in the wake of a morning cold front, but
convection looks to initiate by mid-afternoon as surface flow
veers towards an increasingly upslope direction and daytime mixing
gets going.

The more potent shortwave is progged to traverse NE Colorado this
evening, in tandem with an enhanced surge of moist advection which
may push dewpoints above 60F even into the Denver metro/urban
corridor. Although isolated strong to severe storms will be
possible starting mid-afternoon (30% chance), ingredients look
most aligned during the evening period as bulk shear climbs to
50-60 kts, well depicted by elongated hodographs. This environment
would be favorable for development of intense and (at least
initially) discrete supercells capable of producing very large
hail (over 2-3" in diameter). Similar to yesterday, these will
also carry a damaging wind threat and even potential for a few
isolated landspouts. In contrast to yesterday, the severe threat
will encompass the entirety of the urban corridor, with a
particular focus on areas southeast of and including the Denver
metro. With all of this in mind, an upgrade to an Enhanced (level
3/5) Risk was coordinated with SPC. Activity doesn`t look to
dwindle under after midnight for areas roughly along and south of
I-70. Finally, we`ll see locally critical fire weather conditions
in the high country this afternoon, returning again Wednesday.
More details on that in the Fire Weather Discussion below. We`d
also be remiss not to mention the incursion of smoke from
significant ongoing wildfires in Utah, which is expected to
sustain hazy/smoky sky conditions through the next few days.

A quite similar setup is in store for Wednesday, with an
additional weak shortwave approaching our area and a re-emergence
of a lee cyclone east of the Front Range mountains, feeding
continued unstable conditions and another threat of severe weather
for the lower elevations in the afternoon and evening. Given the
widespread convection expected today into tonight, there`s an
inherent conditional aspect to Wednesday`s setup, but guidance
remains bullish in the convective potential, and deep, abundant
moisture will be present. At first glance, the northeast plains
appear best positioned for a more pronounced severe weather
threat, given presumably lesser thunderstorm coverage today
relative to other areas, as well as the impressive moisture
availability (PW values exceeding 1.25" indicated in most
guidance). Until we are past today`s convection however, it seems
appropriate to continue to message a broad risk of severe weather
for all of our lower elevations Wednesday. Moreover, successive
days of efficient rainmakers will increase the threat of localized
flash flooding from any convection Wednesday, and this will carry
into Thursday when thunderstorms are poised to make a return to
most areas, including our mountains (which will generally stay dry
through tomorrow).

Weaker zonal flow begins to emerge by Friday, and starts to
gradually erode our low-level moisture and severe weather
potential (emphasis on "starts to" - afternoon convection is
still favored, albeit more isolated in nature). Following several
days of cooler conditions, warmer temperatures will return to the
lower elevations. This trend accelerates over the weekend, when
hot and dry conditions will prevail for all areas. Attention will
quickly shift to our mountains, where strong southwest flow ahead
of an amplifying trough will bring widespread critical fire
weather conditions.

&&

.AVIATION /06Z TAFS through 06Z Wednesday/...
Issued at 121 AM MDT Tue Jun 23 2026

A bank of low stratus with bases 005-012 is present over the
Palmer Divide and plains. It has shown some NW-ward expansion over
the past few hours, aligning with the axis of enhanced southerly
winds. There`s around a 30% chance of brief impacts to KDEN if
this southerly flow can hold together long enough before sunrise,
although expected slight veering in the winds over the next few
hours to a more SSW direction is still favored to keep the bulk of
this stratus at bay, just barely. KAPA will see greater potential
for CIG development during this period.

Between 13-14Z, a cold front will reach the terminals bringing a
shift to breezy N winds with gusts 20-25 kts expected. SCT and
perhaps locally BKN clouds with bases 030-050 are anticipated to
spread south following the FROPA, although confidence in any
prolonged CIGS at either of the terminals remains low (~20-30%
chance), thus the TAF favors SCT coverage for now. The threat of
CIGS should diminish by late morning. Expect winds to turn NE then
E through the afternoon/evening, with the caveat of TSRA-driven
outflows becoming increasingly dominant as the afternoon and
evening progresses.

Isolated to scattered -TSRA will develop mid-afternoon (near 21Z)
in the vicinity of the I-25 corridor. Convection in the afternoon
looks rather sporadic and uncertain, hence the PROB30 groups. The
greater potential for widespread and significant convection
(+TSRA, supercells) will begin after 01Z, lasting through ~06-07Z
and being most pronounced for KDEN/KAPA. Temporary vis reductions
wouldn`t be out of the question with the strongest storms.

Lastly, expect increased smoke aloft compared to previous days.
This will likely impact slantwise visibility at times through the
TAF period.

&&

.FIRE WEATHER...
Issued at 121 AM MDT Tue Jun 23 2026

The high valleys and mountains along/west of the Continental
Divide will see two consecutive days of widespread elevated to
locally near-critical fire weather conditions as warm, dry and
breezy conditions persist. The driest conditions are expected
today with humidity lowering to around 10% in the valleys, with
only a slight improvement Wednesday. Wind gusts 25 to 30 mph can
can be expected today, rising to up to 35 mph Wednesday.

Fire weather concerns will be buffered Thursday and Friday as
moisture increases and thunderstorms return. These will be most
widespread Thursday, when they`ll bring localized wetting rains.

Significantly warmer, drier and windier weather will arrive
Saturday and continue into at least Sunday. Wind gusts in the
mountains, including both valleys and higher elevations, are
likely to exceed 40-50 mph (80% chance), sustaining highly
critical fire weather conditions both days.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 8 PM MDT this evening for
COZ212>214-217.

Fire Weather Watch from Wednesday morning through Wednesday
afternoon for COZ212>214.

&&

$$

DISCUSSION...Rodriguez
AVIATION...Rodriguez
FIRE WEATHER...Rodriguez

NWS BOU Office Area Forecast Discussion