415
FXUS65 KBOI 301211
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
611 AM MDT Sun Aug 30 2026

.UPDATE...Updated aviation discussion.

&&

.KEY MESSAGES...
- Cool and dry Sunday then warmer early next week.

- A deeper low pressure system expected later next week for
  cooler, windier, and wetter conditions.

&&

.SHORT TERM /Through Tuesday Night/...
Issued 302 AM MDT SUN AUG 30 2026
An upper level trough and surface cold front exiting to the
east today for cooler and drier air across southeast Oregon and
southwest Idaho. High temperatures today will run around 5 to 10
degrees below normal, with afternoon maximums remaining in the
upper 70s to lower 80s across the Snake River Plain. Calm winds
and clear skies overnight will allow for efficient radiational
cooling, leading to patchy frost in the higher elevation valleys
of southeast Oregon early Monday morning.

A brief upper level ridge builds over the region on Monday,
initiating a rapid warming trend. Highs will climb back near
normal on Monday and rise about 5 degrees above seasonal
averages by Tuesday as thermal ridging shifts east. A large
upper level low pressure system will reach the Pacific Northwest
coast on Monday and begin to advect moisture from the
southwestern U.S. into south-central Idaho. The pressure
gradient between this feature and high pressure to the southeast
will tighten late Tuesday, creating warm and breezy conditions.
Expect southerly to southwesterly wind gusts up to 30 mph across
open terrain and exposed ridges Tuesday afternoon and evening.
Shower chances increase across the western mountain zones
Tuesday as more moisture overspreads the area ahead of the
trough.

&&

.LONG TERM /Wednesday through Sunday/...
Issued 302 AM MDT SUN AUG 30 2026
Model guidance continues to show solid consensus for a long-
wave trough and closed low pressure system to stall near the
Oregon and Washington coastline through the extended period.
This setup keeps the forecast area under persistent, cool
southwesterly flow aloft.

As shortwave energy rotates around the parent low, shower and
thunderstorm chances will increase Wednesday into Thursday,
particularly over southeast Oregon and the West-Central Idaho
Mountains. SW Idaho valley locations may see less widespread
precipitation due to dry slotting between the main circulation
and monsoonal moisture to the east, but cooler temperatures will
be felt region-wide.

Temperatures drop significantly starting Thursday, falling back
to 5 to 10 degrees below normal with valley highs held in the
70s through the weekend. Afternoon gusty winds will remain a
primary feature through late week, particularly across higher
terrain and open valleys of southeast Oregon. Uncertainty
remains regarding exact shower timing into Friday and Saturday
as minor individual impulses traverse the flow, but overall
confidence is high for a cooler and more unsettled pattern
heading into next weekend.

&&

.AVIATION /12Z Sunday through Monday/...
Issued 609 AM MDT SUN AUG 30 2026
VFR. Mostly clear skies today. Light and variable winds. Winds
aloft at 10kft MSL: W 10-30 kt.

KBOI...VFR. Clearing skies. Surface winds: Light and variable
today.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.

OR...None.

&&

$$

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AVIATION.....JDS
SHORT TERM...JDS
LONG TERM....JDS