419
FXUS65 KBOU 250017
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
617 PM MDT Sun Aug 24 2025

.KEY MESSAGES...

- Scattered to numerous showers and thunderstorms through this
  evening. Up to 1-2 inches of rainfall possible in 30 minutes
  from the stronger storms.

- Showers and thunderstorms each day with locally heavy rain, but
  each day comes with several forecast challenges.

- Low confidence in any particular day`s rainfall chances across
  the metro due to poor model consistency. Stronger signal for
  rain across the Front Range mountains through this evening, and
  again by mid/late week.

&&

.DISCUSSION /Through Sunday/...
Issued at 240 PM MDT Sun Aug 24 2025

Water vapor satellite imagery showing a weak shortwave trough
over Utah with lift and numerous showers and thunderstorms across
western Colorado. Over eastern Colorado ahead of the trough, an
outflow boundary from storms over Nebraska and Kansas brought
northeast upslope winds and low clouds. Precipitable water this
morning was 0.75 to 1.00 (in) across eastern Colorado. As moisture
continues to increase, precipitable water climbs to 1.1 to 1.5 (in),
reaching 140 to 180 percent of normal. Numerous
showers/thunderstorms are expected to form across the central
mountains and into the foothills through the afternoon. As the
shortwave tracks eastward, lift and cooling aloft should be enough
to overcome the cap for numerous showers/thunderstorms this evening
along the Front Range and over the eastern plains. A couple
strong/severe thunderstorms will be possible. Very heavy rainfall
will also be possible with 1-2 inches in 30 minutes possible from
the stronger storms. Storm motion looks to be 15 to 25 mph through
mid evening, so this should keep the flooding threat localized. The
storm threat diminishes late this evening, but the chance for light
rain and drizzle will continue through the night.

Monday begins cloudy and cool with areas of drizzle and light
rainfall. The low clouds linger for most of Monday(perhaps all
day) over the eastern plains and urban corridor. One would expect
a cloudy cool day and a capped airmass, which many of the models
show. However, the HRRR and ECMWF (odd combination) show showers
and storms moving off the higher terrain and across the urban
corridor late Monday afternoon and early evening. Will have the
higher PoPs over the higher terrain where numerous showers and
storms are expected and taper then downward heading eastward. The
airmass will remain very moist with heavy rainfall possible.

Upper level ridge slides east over Colorado for Tuesday. Monsoon
moisture remains trapped under the ridge and southeast low level
flow will help keep moisture in the area as well. Precipitable
water values will be above an inch across the Front Range and
eastern plains and close to an 1.5 (in) over far eastern Colorado.
This puts the readings in the 150-180 percentile. The
climatological max for late August on the SPC Sounding Climo page
is around 1.33 (in), which we will be close too. So we have plenty
of moisture in place for showers and storms, however having an
upper level ridge overhead isn`t great for thunderstorm
development. Best chance at breaking the cap will be over the
higher terrain. A light westerly flow aloft is expected around the
high, and could lead to some of the storms drifting off the
higher terrain. The set up for Wednesday is similar, though the
ridging shifts to the southeast and weakens. This may lead to a
better chance for storms off the higher terrain. Still a great
amount of uncertainty these two days. Widespread moderate to heavy
rain is still a possibility with a very moist airmass in place,
but with the lack of a forcing mechanism, heavier rainfall is
expected to be more localized.

For Thursday and Friday, moisture begins to slowly decrease, but
will stay above normal, especially Thursday. The upper level ridge
will settle over the Southern Rockies and Texas with a westerly
flow over Colorado. Scattered to numerous storms are expected to
develop again over the mountains. With westerly steering winds
overhead, these showers/storms will track eastward across the
Front Range and eastern plains. Again the amount of storms is
highly uncertain with low clouds possible due to the moist
airmass. This could cap convection off the higher terrain
either/both/none of these two days.

For next weekend, upper level ridging is expected to develop
across the western states with northwest flow aloft over Colorado.
This should lead to a decrease in moisture over the region.
However, there should be enough moisture still in place for
isolated/scattered showers and thunderstorms each day.
Temperatures will possibly warm a little with drier air in place,
but are expected to be near to slightly below normal.

&&

.AVIATION /00Z TAFS through 00Z Tuesday/...
Issued at 607 PM MDT Sun Aug 24 2025

Showers and a few thunderstorms will be in the Denver area this
evening, decreasing between 04z and 08z. The main impact will be
areas of MVFR ceilings, but variable winds up to 30 knots are
possible (30% chance). MVFR ceilings will prevail later tonight,
with areas of IFR ceilings and possibly LIFR ceilings (50% chance)
between 08z and 15z. MVFR ceilings are expected to prevail through
the day on Monday, with another round of thunderstorms likely
after 21z.

&&

.HYDROLOGY...
Issued at 240 PM MDT Sun Aug 24 2025

Precipitable water values increase to around 150-180% of normal
by late afternoon. Warm cloud depths increase to near 7,000 feet,
so storms will be more efficient rainers with 1-2" possible from
stronger storms in 30 minutes. This could produce some localized
concerns in lower elevations (underpasses/low lying areas), should
stronger storms be able to sustain themselves. Main concerns for
flooding will be across the burn areas.

Monday continues to trend drier with more stable moving in from
the north, but we could still see locally heavy rainfall over the
higher terrain. The better chances for heavy rain on Monday will
be across the southern Colorado mountains. Tuesday and Wednesday
will have the most hydrologic concerns for the mountain burn scars
given richer moisture/instability profiles there versus the
plains. Thursday and Friday are starting to shape up as more
active days again, but a lot of uncertainty with timing of any
potential shortwaves.

&&

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

&&

$$

DISCUSSION...Meier
AVIATION...Gimmestad
HYDROLOGY...Meier