167
FXUS65 KBOU 151136
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
536 AM MDT Sat Aug 15 2026

.KEY MESSAGES...

- Another round of showers and thunderstorms this afternoon and
  evening. A few thunderstorms could become severe, with strong
  winds, hail, and heavy rainfall leading to flash flooding as the
  main threats.

- Monsoon moisture lasts through the weekend, bringing scattered
  showers and thunderstorms again tomorrow.

- Warming and drying trend still set to begin Monday.

- Another active day possible middle of next week.

&&

.DISCUSSION /Through Friday/...
Issued at 126 AM MDT Sat Aug 15 2026

The upper level pattern will remain relatively unchanged today,
with the upper level high off to our southeast and broad troughing
off the West Coast. A weak disturbance will move through the flow
aloft over the area this afternoon. In addition to this, the
upper level jet will be moving off to the northeast, which could
put us in the right entrance region for a brief time this
afternoon. Both of these things will provide upper level support
for shower and thunderstorm development. At the surface, easterly
winds in the afternoon will allow for upslope flow and a continued
inflow of surface moisture. All of these means we`re looking at
another day of scattered to numerous showers and thunderstorms.
The main threat again today will be heavy rainfall leading to
flash flooding (which is discussed further in the hydrology
section of this AFD), but we also have the potential for severe
weather. 0-6km shear will increase for this afternoon, with values
around 30 to 45kts. Instability will be decent, with steep low to
mid level lapse rates and MLCAPEs exceeding 1000 J/kg. Both large
hail and strong winds will be possible with the stronger storms
this afternoon. Shower and thunderstorm activity should start to
weaken and exit our eastern plains around 10PM.

The upper level high will start to push more west on Sunday, turning
winds aloft more zonal rather than southwest. This will bring some
drier air aloft and our PWs will drop a bit closer to normal, but
still remain elevated. Easterly surface winds will allow for some
upslope. Instability and shear will be similar to this afternoon,
if the morning low clouds scatter out fast enough for surface
heating. However, if the low clouds stick around longer than
currently forecast, we could struggle to tap into the higher
instability. Storm coverage looks a bit lower on Sunday compared
to today and yesterday, but we could still see some scattered
activity with a few storms going strong to severe. Heavy rain,
strong winds, and hail will all be threats with this activity.

Drier and warmer conditions are expected for Monday and Tuesday
as that upper high moves closer to the area. Highs on Monday will
be near normal, with highs on Tuesday reaching back into the low
90s or much of the plains. Models are hinting at a weak cold front
and shortwave on Wednesday, which could bring temperatures down a
few degrees and bring back our rain chances. The upper level high
will start to build more north to the west of our area, putting
us in northwest flow aloft. This pattern will favor near to
slightly above normal temperatures and potentially some isolated
storms in the afternoons through the end of the work week.

&&

.AVIATION /12Z TAFS through 12Z Sunday/...
Issued at 504 AM MDT Sat Aug 15 2026

Winds today will generally be light and variable with the
exception of stronger wind gusts from nearby thunderstorms.
Thunderstorms are expected at and around the TAF sites between 20Z
and 01Z this afternoon, before the storms move east. Behind the
storms, winds will return to light and variable. There is
potential for a low stratus deck to develop tomorrow morning, but
right now it looks like it should stay FEW to SCT around 500ft to
1500ft.

&&

.HYDROLOGY...
Issued at 126 AM MDT Sat Aug 15 2026

We`re looking at another potential flash flood day today.
Models are showing slightly lower precipitable water values for
today, but they will still be around 125% to 150% of normal. Warm
cloud depths will be around 4000ft to 6000ft this afternoon.
The stronger storms will be very efficient rainfall producers
again today. Rainfall rates approaching 2" in 30 minutes is not
out of the question. Looking at PMM and various CAM models, a few
localized areas could see storm totals of around 3 inches today.
And to add to all of these ingredients, heavy rainfall over the
past 3 days have increased soil saturation, lowering flash flood
guidance and making many areas more prone to flooding. A Flood
Watch will be in effect from 2PM to 10PM today for the Southern
Foothills, Palmer Divide, and all of our eastern plains counties.
I do want to make sure to emphasis that it is unlikely that
everywhere in the Flood Watch will see heavy rain today. It is
extremely difficult to forecast exactly where the heaviest rain
will fall, but with the rain the past 3 days and the moisture we
still have available, anywhere in the Watch could see Flash
Flooding today if one of the stronger storms moves over that area.

The threat for heavy rainfall and flash flooding will continue
for Sunday afternoon and evening. However, PWs will continue to
trend downward and the coverage of showers and storms looks to
decrease for Sunday compared to today and yesterday, so flooding
concerns will be lower.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 2 PM MDT this afternoon through this evening
for COZ036-038>051.

&&

$$

DISCUSSION...AP
AVIATION...AP
HYDROLOGY...AP

NWS BOU Office Area Forecast Discussion