National Weather Service Raw Text Product

225 
FXUS65 KBOU 291640
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1040 AM MDT Tue Jul 29 2025

.KEY MESSAGES... 

- Heavy rain and flash flood threat increasing over the Palmer
  Divide area this afternoon and evening. 

- Cooler, wetter and more active pattern today through Friday, 
  particularly east of the Continental Divide.

- Afternoon showers and thunderstorms each afternoon (20-80%
  chance) with main threats lightning, strong/gusty winds, and
  localized flash flooding.

&&

.UPDATE...
Issued at 1039 AM MDT Tue Jul 29 2025

Lower to mid 60s dewpoints continue to be advected in across the
plains. Main frontal push has shifted south of our forecast area,
but will likely stall just to the south this afternoon with
increased daytime heating/mixing in southeast Colorado. We're at
120-140% of normal for precipitable water, and forecast warm cloud
depths increase to 7000-8000 feet - an impressive value. Thus, the
ingredients for storms with locally heavy rain and flash flooding
exist. However, we will be more stable due to stratus, and that
stability is currently observed on ACARS soundings. Therefore, 
stronger storm development will likely be limited to near or just 
south of the crest of the Palmer Divide. Some of those storms may 
attempt to push northeast in the mean flow, but highest threat of 
storms with very heavy rain should stay focused toward the higher 
terrain and more unstable airmass to the south. We coordinated 
with the Pueblo, CO office and opted for a Flood Watch for flash 
flooding for eastern Douglas, Elbert, and Lincoln Counties. Still 
a non- zero threat for locations farther north including Denver 
due to the ingredients, but at this time we think the highest 
threat will stay to the south/southeast and closer to the 
instability axis. Also, a narrow ribbon of MLCAPE of 2000 J/kg and
weak CIN expected, so a couple pulse severe storms possible 
(again mainly southeast of Denver). There is also some chance that
stronger storms/locally heavy rain develop east/northeast into 
the far east/northeast plains of Colorado this evening. Will 
continue to monitor. 

UPDATE Issued at 254 AM MDT Tue Jul 29 2025

A cool front has moved across the area early this morning which has 
led to increasing low level moisture with dewpoints in the 60's. 
This will allow for MLCAPE to rise up to 1500 j/kg over the plains 
this aftn with potential up to 2000 j/kg. Overall, the flow aloft
is rather weak and bulk shear values are low. However, with this 
amount of instability certainly can rule out a few marginal svr 
storms. Meanwhile, PW values will rise up to 1.25" over the 
plains so storms will produce decent rainfall with some localized 
flash flooding possible. Sct storms will develop along the I-25 
Corridor and Palmer Divide by early to mid aftn and then increase 
in coverage as they move across the plains from late aftn thru the
early evening hours. 

&&

.DISCUSSION /Through Monday/...
Issued at 205 PM MDT Mon Jul 28 2025

The ridge at 500mb remains centered over the Central Plains 
tomorrow with a trough off the U.S. West Coast. Tonight a shallow 
cool front will move south across the area, east of the Divide. 
The frontal boundary will shape our weather for much of the week 
as it stalls somewhere along the Oklahoma border for much of the 
week, allowing low-level moisture and not-so-hot air to work 
westward throughout much of the period. Starting tomorrow, 
easterly winds across the plains will advect surface dewpoints in 
the mid 60s (northeast plains) to upper 50s along the I-25 
corridor. Not surprisingly this should result in PW values up to 
an inch east of the Divide, and 1.25" across the northeast corner 
of Colorado. Afternoon thunderstorms will be much more widespread 
than the past several days, and there should be plenty of 
instability around to get storms going, with around 1000 J/kg 
SBCAPE east of the Divide, and up to 1400 J/kg SBCAPE across the 
northeast corner. However, effective bulk shear will be 15-20 kts 
given the position of the ridge; thus lightning, strong/gusty 
winds, and heavy rain will be the main threats throughout the 
afternoon. PoPs will be high but it will still be hit or miss 
given the weak shear and expected strong cold pools. We expect 
storms to form across the mountains around noon and drift east- 
northeast throughout the afternoon, with movement and development 
tied to gustfronts. The best chance for TSRA across the northeast 
corner will be in the late evening when gust fronts finally make 
it eastward. The West Slope unfortunately does not have anywhere 
near as much PW or low-level moisture, so just isolated 
thunderstorms are possible (20-40%) on Tuesday. A final note on 
Tuesday's forecast is on the smoke from wildfires in Utah and 
Arizona. The HRRR smoke brings quite a bit of smoke aloft into our
area Tuesday afternoon and evening. The northern quarter of 
Colorado will see the most smoke tomorrow afternoon/evening, but 
in general the nears-surface smoke levels shouldn't get too high. 
You will definitely notice the hazy skies and orange sunset 
tomorrow. We've including areas of smoke in the wx grids. Highs 
will also be cooler than today with 80s expected across the plains
and mountain valleys, and close to 90 across the northeast 
plains.

Wednesday will be more of the same with continued high PW values of 
an inch or more east of the Divide.  There is a much better upslope 
component out of the east Wednesday afternoon which will no doubt 
increase thunderstorm coverage starting in the mountains midday then 
migrating east.  Surface dewpoints should be in the upper 50s across 
the plains.  Flow aloft is still weak so lightning, strong winds, 
and heavy rain will be the main threats. Given these ingredients, 
WPC has put our area in a slight risk of excessive rainfall.  Warm 
cloud depths still look pretty shallow, otherwise we'd be much more 
concerned about a widespread flooding threat.  As it stands, a few 
localized areas could exceed an inch and see some flash flooding, 
but in general widespread precipitation amounts should be much less 
than that. Precipitation amounts will be light across the West Slope 
once again given much less moisture.  High temperatures should 
remain in the low to mid 80s with extensive cloud cover and rain-
cooled outflows. The mountain valleys should see upper 70s to low
80s.

Thursday and Friday look to be much of the same.  Ample moisture 
around for afternoon thunderstorms both days.  The heavy rain threat 
looks a little less both afternoons with more southeast flow across 
the plains and the likely development of a Denver Cyclone, which 
will tend to focus storms and heavy rain across the east side of 
metro Denver and Greeley, and points east.  Interestingly on Friday 
significantly more shear will be in place because a weak trough 
moves across Wyoming earlier on Friday, with stronger northwest 
winds on the backside of that weak trough. With 1000-1600 J/kg 
SBCAPE possible on Friday afternoon there could be some borderline
severe weather if the shear increases by the afternoon hours. 
Both days will have ample cloud cover in the afternoon and with 
700 mb temps remaining "cool" for late July around +12 to +14, 
high temperatures should continue to be below normal with highs in
the 80s across the plains and I-25 urban corridor, and 70s to low
80s for the mountain valleys.

This weekend looks drier and warmer than the workweek, with the 
ridge centered over Colorado.  Still a chance of weak afternoon 
showers/thunderstorms but it looks more likely that 90s will return 
to the plains and I-25 urban corridor, with the NBM showing 50-70% 
chance of 90 degF+ on Saturday and 70-85% on Sunday for elevations 
below 6,000 ft.

&&

.AVIATION /12Z TAFS through 12Z Wednesday/...
Issued at 514 AM MDT Tue Jul 29 2025

There is stratus lurking around but mid and high level clouds are 
preventing me from seeing exactly where it's at on satellite. For
now have kept in a tempo group thru 16z in case it does move in 
from the north. Later today will see sct tstms develop by 20z or 
21z but best chc may stay south and east of DIA. Current timing 
suggests activity would move east of the area by 00z. Winds will 
be light north this morning and then become more NE by midday. 
Naturally outflow boundaries will lead to gusty winds and erratic
directions at times thru 00Z. Winds by mid evening should trend 
to more southerly. 

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 9 PM MDT this evening for COZ041-046-047.

&&

$$

UPDATE...Barjenbruch
DISCUSSION...Schlatter
AVIATION...RPK