479
FXUS65 KPIH 041131
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
531 AM MDT Fri Sep 4 2026

.KEY MESSAGES...

- Mountain Showers and Lower-Elevation Warmth (TodaySaturday):
  Broad cyclonic flow around a Washington low will keep showers
  and thunderstorms active over the Central Mountains for the
  next 36 hours. Elsewhere, dry conditions will prevail as
  valley highs climb into the 80s.

- Breezy Sunday Ahead of Main System: Southerly winds will
  increase on Sunday, pushing temperatures into the 80s under
  increasing clouds, with widespread rain holding off until late
  Sunday evening.

- Widespread Labor Day Rain and Brief Cooldown (Late
  SundayMonday): As the upper low shifts east, widespread rain
  (0.25" to 0.50" average QPF) will overspread eastern Idaho
  late Sunday into Monday, dropping high temperatures into the
  60s and lower 70s.

- Quick Mid-Week Warming Trend: Precipitation wanes late Monday
  as the system exits into Alberta, paving the way for a rapid
  warm-up back into the 80s by Wednesday as high pressure
  rebuilds over the Southwest.

&&

.DISCUSSION...
Issued at 319 AM MDT Fri Sep 4 2026

Eastern Idaho remains positioned along the eastern periphery of
a broad, persistent upper-level low centered over western
Washington. Southwest-to-westerly cyclonic flow around this
system will continue streaming waves of shortwave energy over
the Central Mountains, maintaining shower and thunderstorm
chances over the next 36 hours. Outside of the central mountain
terrain, dry conditions and variable mid-to-high level cloud
cover will prevail. Daytime maximum temperatures will climb back
to near 80 degrees across the lower Snake Plain and areas
toward the Utah border today, expanding into widespread 80s
across the Snake Plain and Magic Valley on Saturday. Mountain
precipitation will briefly wane Saturday afternoon as the parent
low begins a slow eastward translation across the Pacific
Northwest.

Temperatures will continue their upward trend on Sunday as
southerly flow strengthens ahead of the approaching trough,
boosting valley highs into the 80s amidst breezy afternoon
winds. Increased cloud shading and widespread precipitation will
hold off through most of the day, preserving favorable outdoor
conditions until late Sunday evening. Moisture and dynamic lift
increase sharply Sunday night through Labor Day Monday as the
trough axis crosses Idaho. Operational models and ensemble
guidance display ongoing spread regarding QPF totals: the ECMWF
maintains a wetter solution compared to the drier GFS. A middle-
of-the-road consensus blend remains in place, forecasting
roughly 0.25" to 0.50" of wetting rain across much of eastern
Idaho, though these totals remain subject to adjustment as
guidance converges. Extensive cloud cover and rain will cap
Monday highs in the 60s to lower 70s. As the core low lifts into
Alberta late Monday afternoon, precipitation will diminish from
west to east alongside clearing skies.

Conditions dry out rapidly on Tuesday as temperatures begin a
fast recovery under rising 500 mb heights. Global ensembles show
high-pressure ridging attempting to rebuild across the
Southwestern U.S. mid-to-late week, positioning eastern Idaho
along the northern margin of the ridge axis. Model guidance
displays noticeable spread regarding how aggressively the ridge
amplifies, but lower elevations are forecast to return to the
lower 80s as early as Wednesday, with potential to trend even
warmer if the ridge axis shifts further north. Southwest flow
aloft along the ridge periphery will keep low-end, daily
precipitation chances in the forecast for higher terrain zones
through late week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 525 AM MDT Fri Sep 4 2026

A brief period of gusty continues this morning. Those winds
should weaken later this morning and become around 10 kts for
the rest of the period. Some showers may approach SUN at times
today but should be of little impact. VFR expected to prevail at
all terminals.


&&

.FIRE WEATHER...
Issued at 319 AM MDT Fri Sep 4 2026

Convective activity over the next 36 hours will remain largely
restricted to the Central Mountains, while lower elevation zones
experience warm, dry conditions with highs in the 80s.
Increasing southerly winds on Sunday will precede a strong
atmospheric moisture surge Sunday night into Labor Day Monday,
delivering widespread wetting rains (0.25"0.50" QPF) and
excellent relative humidity recoveries across all dispatch
zones. Drier, significantly warmer conditions return mid-week.

&&

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

&&

$$

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