978 
FXUS65 KBOU 232355
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
555 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 /00Z TAFS through 00Z Thursday/...
Issued at 555 PM MDT Tue Jun 23 2026

Thunderstorms are still expected across eastern Colorado this
evening, though direct impacts to BJC and APA are a significantly less
likely than earlier today, so we are using PROB30 for their -TSRA
chances. WoFS and the latest CAMS have severe thunderstorms 
developing north of DEN around 03Z. They should move southeast at
20 kts and may not directly impact DEN, but of course they could 
and if they do large hail and wind gusts to 50 kts are in the 
realm of possibility, all between 04Z and 07Z. For sure outflow 
from those storms will impact DEN where anywhere from southeast 
to northeast winds gusting 25-30 kts are expected as the storms 
move east and southeast of DEN. Winds at APA and BJC should not be
as strong after 06Z (under 15 kts) as they will be further 
removed from the severe storms. Cool outflow from the severe 
storms is expected to generate a short-lived stratus deck at the
terminals. Low confidence in the stratus deck but NBM CIG 
forecasts have consistently generated this stratus. Assuming it 
forms, it shouldn't last more than 3-5 hours, scattering out 
before 12Z.

Tomorrow, convection should be well east of our area after 10Z, 
and south winds should return to APA and DEN mid morning. A 
Denver Cyclone looks to form tomorrow morning and move near DEN 
between 15-17Z. It is very hard to predict how it will evolve but 
CAMS have the cyclone remaining west of DEN, which would result in
east or southeast winds at DEN 10-12 kts from midday into the 
early afternoon. APA will be more south to southeast, and BJC will
be north. A warm and uncapped environment tomorrow means 
thunderstorm chances are 50/50 at the terminals starting at 20Z. 
At least one round between 20-23Z is possible with gusty winds 
35kts or more, and even possibly severe sized hail. There are 
indications of a second round of storms, not as strong, after 03Z.
The storms that get going tomorrow afternoon are most likely to
develop west winds behind a gustfront or gust fronts, but there
should be a return to east winds 10-20kt after 00Z/02Z from 
outflow coming back west from severe storms well east of the 
terminals.

&&

.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