795
FXUS65 KBOU 272025
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
225 PM MDT Wed Aug 27 2025

.KEY MESSAGES...

- Scattered to numerous storms through Thursday with locally heavy
  rainfall. Some potential for burn area flash flooding and
  street/lowland flooding with any of these storms.

- Gradual drying trend through the weekend, but still at least
  scattered storms each afternoon and evening.

- Warmer and drier by early next week.

&&

.DISCUSSION /Through Wednesday/...
Issued at 225 PM MDT Wed Aug 27 2025

Scattered thunderstorms, some with very heavy rain, have developed
early this afternoon and trend should continue through the rest of
the afternoon. We have now warmed sufficiently to greatly weaken
or eliminate the cap, so we are primed for convection in the lower
elevations. Storms will be intense, with high precipitable water
and MLCAPE around 1000 J/kg and sufficient shear to keep updrafts
in tact, heavy rain is becoming more likely. See the Hydrology
portion of this forecast discussion for more details. Storm
coverage should also be greater considering synoptic scale lift
(at least along/north of I-70) in the left exit region of the
upper level jet. Thus, one if not two batches of showers and
thunderstorms can be expected from this afternoon into this
evening, with the storms likely organizing further as they push
E/SE across the plains this evening. A few showers may linger
overnight with brief light rain or sprinkles.

Thursday should feature similar conditions to today, although the
upper level jet shifts northward, and puts us in weak subsidence.
Thus, coverage should decrease and there may be a slightly
stronger cap to overcome. However, storm intensity should remain
with just as much MLCAPE and shear.

Models are consistent with slight drying starting Friday and
lasting into Saturday. This occurs as flow aloft transitions to
more westerly Friday and then northwesterly Saturday. While storm
coverage and intensity should gradually decrease, there is
potential for an embedded disturbance on Saturday which could
bring a brief uptick in coverage again.

Sunday is almost certainly shaping up drier (80% confidence) per
ensemble output, and thus much lower chances of precipitation.
Temperatures will then warm through Monday and Tuesday with highs
averaging around the mid 80s in lower elevations. While it`s
early, there are some models showing a taste of fall reaching the
Central and Northern Plains toward the middle of next week.

&&

.AVIATION /18Z TAFS through 18Z Thursday/...
Issued at 1156 AM MDT Wed Aug 27 2025

First concern is for thunderstorms this afternoon. Morning stratus
has kept the boundary layer cool. However, we are now near full
sunshine and warming, so if we hit upper 70s (which we should do)
the cap would be broken. That`s not a guarantee of course,
depending on how clouds evolve, but there is also synoptic lift so
that should add to coverage. As a result, we`ll use TEMPO TSRA
for the most likely time period 21Z-01Z. Just like yesterday, if a
storm core moves over the airport, then visibility could drop to
<1SM in +TSRA.

Next concern will be for patchy fog and areas of stratus again
overnight given moist boundary layer and expected rainfall. While
there`s some threat as soon as skies clear after midnight, the
main threat would be 11Z-15Z. Winds appear to be slightly less
favorable than last night, but so light that patchy fog could
essentially develop anywhere. And, enough threat of a weak wind
shift to NW late that fog could easily spread back to KDEN so
we`ll go with TEMPO BR and LIFR ceiling.

Any fog/stratus is expected to lift a little quicker Thursday
morning since it will be shallow. Another round of scattered
storms expected Thursday afternoon mainly after 21Z.

&&

.HYDROLOGY...
Issued at 225 PM MDT Wed Aug 27 2025

As discussed above, storm intensity will be higher into this
evening as they move east through the I-25 Corridor and onto the
plains. Precipitable water (PW) is near 150% of normal, and warm
cloud depths are near 5,000 feet (good but not exceptional for
heavy rain). While storms will be strong enough to drop very
heavy/torrential rain (rain rates 1.25-2.0 inches in 30-45
minutes), we think the overall flash flood threat for lower
elevations will remain slightly limited by faster storm motion
today. That would be just enough to preclude a Flash Flood Watch.
That said, street/lowland minor flooding will be likely with the
stronger storms and we`ll cover much of these impacts with
Urban/Small Stream Flood Advisories. One or two Flash Flood
Warnings would still be possible but generally small/isolated
locations due to overall speed of storms - as long as they don`t
train/stall in any given location.

Thursday afternoon and early evening will see about the same
setup as today with regard to storm intensity, although coverage
should be a little lower.

A gradual drying trend will still occur Friday into Saturday with
lower hydrologic impacts from storms.

&&

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

&&

$$

DISCUSSION...Barjenbruch
AVIATION...Barjenbruch
HYDROLOGY...Barjenbruch