357
FXUS65 KPIH 271905
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
105 PM MDT Sun Sep 27 2026

.KEY MESSAGES...

- Nighttime Showers East of I-15: An approaching upper-level
  trough will increase clouds tonight, bringing a brief round of
  showers and isolated thunderstorms primarily along and east
  of the I-15 corridor, focusing over the Eastern Highlands.

- Noticeably Cooler Monday: Showers exit rapidly Monday with
  clearing skies. Post-frontal air will drop valley daytime
  highs into the 60sroughly 10 degrees cooler than today`s
  readings.

- Early October Warming Trend: High pressure builds over the
  Intermountain West starting Wednesday, keeping the remainder
  of the 7-day forecast completely dry while pushing lower-
  elevation highs into the mid-to-upper 70s by late week.

&&

.DISCUSSION...
Issued at 101 PM MDT Sun Sep 27 2026

Afternoon satellite imagery shows increasing cloud cover across
eastern Idaho as southwesterly flow strengthens ahead of an
approaching upper-level trough. Temperatures have climbed into
the 60s across lower elevations and will reach the 70s before
peak diurnal heating concludes. As the trough axis approaches
tonight, cloud cover will thicken, bringing a brief return of
showers and potential isolated thunderstorms to the eastern half
of the forecast area. The highest precipitation probabilities
will align along and east of the I-15 corridor, with the Eastern
Highlands serving as the primary focus area. This feature will
move through quickly, with clearing conditions spreading across
the region throughout the daytime hours on Monday. The system
will usher in a cooler air mass, dropping valley highs back into
the 60s on Mondayapproximately 10 degrees below today`s
maximums.

Upper-level flow transitions to predominantly zonal Tuesday
into Wednesday as high pressure begins to organize over the
Southwestern U.S.. Temperatures will hover near seasonal
climatological norms for the first part of the workweek,
accompanied by dry conditions and light surface winds. Upper-
level ridging will build directly over the Intermountain West
starting Wednesday and remain established through next weekend.
This will drive a warming trend that will push afternoon
temperatures above seasonal averages. Highs in lower-elevation
valleys will reach the mid-to-upper 70s by Thursday and hold
there through the weekend. With atmospheric moisture shunted
well away from the region, the forecast remains completely void
of precipitation chances beyond Monday, ensuring a dry,
pleasant start to October.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1134 AM MDT Sun Sep 27 2026

VFR conditions will continue at all sites through the forecast
period. Moisture spreading into the region will allow for SHRA
to develop across the region this evening. The best chances for
predominate SHRA will be at DIJ overnight but will carry VCSH at
all sites. Cannot completely rule out ISO TSRA, but confidence
is low. Precipitation shifts east of the region during the
morning Monday.

&&

.FIRE WEATHER...
Issued at 101 PM MDT Sun Sep 27 2026

Moisture streaming into East Idaho will allow for showers and
isolated thunderstorms overnight. Slightly cooler temperatures
arrive Monday behind the departing system. A shallow ridge of
high pressure builds back into East Idaho for much of the week,
with a gradual warming trend and dry conditions. Models have
backed off on a system for the weekend and are now just swinging
a weak system past to the north, so precipitation chances have
lessened.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...McKaughan
AVIATION...DMH
FIRE WEATHER...DMH