471
FXUS65 KBOU 210548
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1148 PM MDT Wed Aug 20 2025

.KEY MESSAGES...

- One more hot day today with near record heat.

- Cooler and wetter weather arrives this weekend, lasting through
  at least the middle of next week.

- A few stronger/severe storms and heavy rain possible Friday,
  Saturday, and Sunday.

- Locally heavy rainfall more likely by Monday.

&&

.DISCUSSION /Through Wednesday/...
Issued at 225 PM MDT Wed Aug 20 2025

Summer heat and dryness will remain in place through Thursday, but
a significant change to a cooler and wetter weather pattern is
still expected for this weekend and at least the first half of
next week.

The upper level high will remain parked across Colorado tonight
and Thursday, keeping summer heat in full force and also preventing
much in the way of shower/storm development. Highs will soar into
the mid to upper 90s across the plains, approaching records for
the date (Denver`s is 99F set in 2023). Only an isolated late day
shower/storm will be possible over the mountains again on
Thursday, although a slight chance (10-15%) that something could
move off the higher terrain by Thursday evening as the cap weakens
late in the day.

Bigger changes are still forecast to start Friday, when a cold
front arrives by early morning. That means temperatures will start
to cool and moisture will increase in the post frontal airmass.
That leads to a higher chance of storms for the afternoon and
evening hours. Depending on temperatures and instability behind
the front, a couple of these storms could be strong or even
severe. MLCAPE looks on the marginal side (<1200 J/kg), but at the
same time bulk shear increases to 30-40 kts in strengthening
west/northwest flow aloft. Precipitable water (PW) values also
increase sharply, so storms will be capable of producing locally
heavy rain as well.

The flow aloft strengthens greatly over the Central and Northern
Plains during the weekend, which would support additional backdoor
cold fronts to move across the plains and back into the Front
Range. As a result, temperatures will remain below normal for
this period, and low level moisture should be reinforced. It was
interesting to see some ensemble members suggest a slight rebound
in temperatures and thus instability on Sunday. All in all, it
will be cooler with at least a chance of showers/storms each day.
Given the pattern, we wouldn`t be surprised to see Saturday`s
higher precipitation coverage to shift to the southwest of Denver,
while Sunday`s coverage may be more scattered but slightly
stronger if we can get enough heating.

What the ensembles were very consistent with and converging on
was the increase in shower/storm coverage and heavy rain threat
for Monday. Another surge is advertised to push south across the
Central Plains, increasing upslope flow. At the same time, weak
QG lift remains in place to support higher coverage of
showers/storms. A look at the ensemble`s PW shows rather
impressive values of 1.2-1.25" on average along the Front Range,
or 150-200% of normal and near climatological maximums. Also,
taking a quick look at soundings shows potential for moist
adiabatic/skinny CAPE profiles and deep warm cloud depths, all
favorable ingredients for heavy rain producing storms. Something
we`ll certainly keep an eye on. At this point, the highest heavier
rain threat should be shifting south/southwest of our forecast
area Tuesday and Wednesday, but still some threat depending on
how progressive the trough/ridge pattern is.

Temperatures will remain below normal through at least the middle
of next week. Finally, if more widespread precipitation/stratus
does occur, it`s not impossible that either Monday or Tuesday
could end up with highs staying near/below 70F on the plains and
I-25 Corridor. We`re almost a lock for 70s (or cooler).

&&

.AVIATION /06Z TAFS through 06Z Friday/...
Issued at 1143 PM MDT Wed Aug 20 2025

VFR through the TAF period. Drainage winds will become much
lighter at DEN and APA between 10-13Z. Winds will shift to the
northeast late this morning and will be persistent throughout the
afternoon. Tonight, a push of southeasterly winds will arrive in
the evening. Then, a cold front will shift winds to the north or
northwest between 06-09Z.

&&

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

&&

$$

DISCUSSION...Barjenbruch
AVIATION...Danielson