898
FXUS65 KBOU 231906
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
106 PM MDT Tue Jun 23 2026

.KEY MESSAGES...

- Widespread severe thunderstorm risk for all of the lower
  elevations starting mid-afternoon today and into the overnight
  period. 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 Wednesday. Fire danger increases considerably this weekend,
  as much hotter, drier and winder weather arrives.

&&

.DISCUSSION /Through Tuesday/...
Issued at 1255 PM MDT Tue Jun 23 2026

The busy week of severe weather rolls on for our area with today
likely bringing the highest risk of the week for the urban corridor.
This is a complex forecast given the risk each day will depend on
earlier convection. Thus, the risk for this evening will depend on
how the afternoon evolves, but multiple rounds of strong to severe
thunderstorms are possible today. Following this morning`s cold
front, winds are northeast and eventually are expected to turn to
the east behind an outflow boundary from storms in Kansas and
Nebraska by later this afternoon. This will further advect moisture
into our area. A subtle shortwave trough should move across northern
Colorado this evening providing better lift to the area.

The ingredients look to be in place for a potentially lengthy severe
weather threat today, but a strong cap is currently in place that
will need to be overcome this afternoon/evening. Unusually high
dewpoints for our area (> 55 degrees) are possible for much of the
day into the evening. MLCAPE values could exceed 1500-2000 J/kg for
much of the afternoon and evening across the entire plains. 0 to 6
km bulk shear will be around 50 to 70 kts, possibly even reaching 90
kts. 0 to 3 km storm relative helicity values could be around or
even slightly exceed 100 to 200 m2/s2. CAMs are showing a wide
variety of solutions, especially once we reach this evening, likely
due to the aforementioned potential for a cap to be in place as well
as the strength/timing of the shortwave. With the incoming
shortwave, we believe the cap should be able to be overcome, leading
to widespread showers and thunderstorms tonight and overnight.

The Storm Prediction Center has included nearly the entire I-25
corridor and plains in an enhanced (3/5) risk for today. The
greatest threats today will be large hail (2 inches or greater in
diameter followed by damaging wind gusts (> 70 mph). There is also
the threat for a tornado or two and/or landspouts.

Isolated to scattered storms are expected to initiate along the
Cheyenne Ridge and Palmer Divide around 1pm to 4pm this afternoon.
By this evening, as the better lift arrives, convection should
increase in coverage along the I-25 corridor and move through our
area from NW to SE. The highest threat window for the Denver metro
would be between about 9pm and 3am tonight with the threat
continuing possibly through as late as sunrise for our far
southeastern plains. We want to emphasize that this is a somewhat
unusual nocturnal threat for our area.  Large hail looks to be the
main impact from evening and overnight convection.

The flooding threat will increase as the week goes on given the
amount of rainfall that has fallen, especially on the eastern
plains, where 0.25-0.50" has already fallen in the last few days.
Even tonight, some areas on the eastern plains could see a quick
inch of rainfall. Between Wednesday and Thursday, some areas could
pick up an additional 1 to 1.5 inches of rainfall.

A Red Flag Warning remains in effect for today for the mountains due
to the threat of locally critical fire weather conditions. This
threat will continue tomorrow. See the Fire Weather Discussion for
more details. Wildfires in Utah will continue to produce smoke and
the flow aloft will carry it into Colorado for at least the next few
days. While the near surface smoke density looks quite minimal, the
smoke will be thicker at mid and high levels and will keep some hazy
conditions around the area particularly each night and early morning.

Wednesday and Thursday will continue to bring a risk for severe
weather as shortwaves continue to rotate around the high pressure
centered in Texas. Thus, much of the plains is already highlighted
in a slight (2/5) risk from the Storm Prediction Center for
Wednesday and Thursday. The threat each day will evolve based on how
previous convection plays out. We currently expect dewpoints in the
50s and low 60s to continue as well as MLCAPE values between 1000
and 2000 J/kg particularly on Wednesday with only slightly lower
dewpoints and MLCAPE on Thursday expected as of now.

Friday through the weekend should bring less showers and
thunderstorms, but there will still be a chance especially for the
eastern plains, given only zonal flow aloft. The heat will return
for the weekend into next week with temperatures well into the 90s
forecast as the ridge builds to our east. Fire weather concerns will
also increase for the mountains and mountain valleys on Saturday and
Sunday, looking increasingly concerning due to some stronger wind
gusts.

&&

.AVIATION /18Z TAFS through 18Z Wednesday/...
Issued at 1209 PM MDT Tue Jun 23 2026

Very complicated convective forecast for this afternoon and
overnight. First, the winds. Behind the front this afternoon winds
will gradually go from NE to E by 00Z. Winds could increase late
this afternoon to the 10-15 kt range with gusts as high as 25 kt
at DEN and APA. CAMs are all over the place with convective
initiation which isn`t surprising given the stable airmass post
frontal, time it takes to warm up post-frontal, and various
moisture surges coming from the east. Only a few models break out
convection before 00Z, and a majority have robust convection
across the plains of Colorado after 02Z. In fact, a recent run of
the HRRR places a supercell just north of DEN at midnight.
Needless to say, extremely low confidence in the timing of any
convection near the terminals. BJC seems to have the least chance
given no CAMS break out convection over the foothills this
afternoon into overnight hours. The Palmer Divide looks like a
good place for initiation which is why we have a TEMPO group for
TSRA this evening at APA. Any storms that fire near the terminals
this evening through midnight have the potential for gusty winds,
large hail, and plenty of lightning. Any convective activity
should be east of the terminals by 07Z, but even that is not for
certain. There could be another east surge after midnight that
fires another round of thunderstorms but for now the chances are
too low to include in the TAFs.

Models indicate a brief period of stratus with one of those
easterly surges. Best bet on timing is after 07/08Z. For now the
stratus doesn`t look to hang around more than 3-6 hours, and
should be scattered out by 12Z but also there is low confidence in
that.

On Wednesday a Denver Cyclone will form southwest of Denver and
move over or near DEN late morning. As a result winds will go
from south to east by midday, then maybe north by early
afternoon. APA will be in the north winds much sooner than KDEN
given the expected movement of the cyclone. We also expect
thunderstorms to form during the afternoon hours near or over all
three terminals after 20Z, this time with a threat of wind gusts
to at least 35 kts.

&&

.FIRE WEATHER...
Issued at 1255 PM MDT Tue Jun 23 2026

Widespread elevated to critical fire weather conditions are
possible each of the next two days in the mountains and mountain
valleys. Humidity will drop to around 10% in the valleys today,
with only a slight improvement Wednesday. Wind gusts up to 35 mph
are possible today with only slightly lower wind speeds on
Wednesday.

Fire weather concerns will be very low on Thursday and Friday as
moisture increases and thunderstorms return. These will be most
widespread Thursday with localized wetting rains.

Warmer, drier, and windier weather remain increasingly likely for
Saturday, Sunday, and early next week. 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 until 8 PM MDT this evening for COZ212>214-217.

Fire Weather Watch from Wednesday morning through Wednesday
afternoon for COZ212-213.

Red Flag Warning from 11 AM to 6 PM MDT Wednesday for COZ214.

&&

$$

DISCUSSION...MV
AVIATION...Schlatter
FIRE WEATHER...MV

NWS BOU Office Area Forecast Discussion