960
FXUS65 KPIH 211130
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
530 AM MDT Fri Aug 21 2026

.KEY MESSAGES...

- Heat Advisory has been expanded to include more areas for
  today. Afternoon temperatures start a cooling trend Saturday.

- A overall slight chance risk of thunderstorms today, a chance
  risk for Saturday in many places. Risk decreases slightly for
  Sunday.

- Breezy and gusty afternoon Sunday.

&&

.DISCUSSION...
Issued at 224 AM MDT Fri Aug 21 2026

Today through Sun night...The upper level ridge overhead
reaches its peak strength today, then a Pacific coastal low
slowly shift eastward and starts to break down this very strong
ridge. This brings in lower 500mb heights in eastern Idaho, and
a stronger shift to southerly flow that allows remnants of the
southwest monsoon to move into eastern Idaho. This will trigger
thunderstorms even today, but even greater risk on Sat. The
continued shift of the pattern eastward will mean lowered risk
for thunderstorms in the western portion of the forecast area.

Temperatures continue very hot today, but the declining 500mb
heights, along with increased cloud cover on Sat and Sun, bring
a cooling trend to the high temperatures. The Heat Advisory will
not be needed after today.

The shift in the pattern will also bring gradually stronger wind
as the upper level low attempts to move inland. Expect gusty
wind to develop on Sun afternoon.

Mon through Thu Night...The formerly coastal upper level low
will break down the upper level ridge as it moves into southern
Canada and moves through eastern Idaho longitudes up there. This
will bring up moisture from the southwest monsoon each day, with
declining moisture reducing the threat starting Tue afternoon,
but not ending it. Wind stays light until Thu afternoon, but
even then only breezy conditions expected.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 525 AM MDT Fri Aug 21 2026

Clouds will leave this morning, then come back tonight, bringing
SHRA. Low chance of TS as well but only mentioned in KDIJ where
the probability reaches even close to 30 percent chance. The
clouds this evening could develop CIGs, but should stay above
FL100. No impact to VSBY expected, although FU could be a fly in
the proverbial ointment. Wind outside of TS should be light and
mainly variable, especially during the daylight hours today. A
more southerly component should develop during the overnight
hours.

&&

.FIRE WEATHER...
Issued at 224 AM MDT Fri Aug 21 2026

Despite the very hot temperatures, the movement of moist air
from the southwest monsoon into the Gem State means that there
are only limited areas of low humidity that reaches critical
levels starting Sat afternoon. This is also due to low pressure
moving in from the west that brings cooler air. The trade-off is
greater thunderstorm coverage on Sat afternoon and evening,
likely needing Red Flag Warnings for areas with critical fuels.
Expect breezy conditions in portions of the Snake River plain on
Sun afternoon, but afternoon humidity will be in the 20 percent
range. The thunderstorm pattern shifts to the east on Sun,
leaving mostly slight chance-level of thunderstorm activity in
all but the Eastern Idaho Dispatch area, where it will be close
to critical thunderstorm criteria.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 10 PM MDT this evening for
IDZ051>059-061-062-064-065-067-075.

&&

$$

DISCUSSION...Messick
AVIATION...Messick
FIRE WEATHER...Messick