819
FXUS65 KBOI 211230
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
630 AM MDT Fri Aug 21 2026

.UPDATE...Updated aviation discussion.

&&

.KEY MESSAGES...
- Heat Advisory through this evening in the Treasure Valley,
  western Magic Valley, and Upper Weiser River Valley.

- Monsoon moisture will bring a chance of showers and
  thunderstorms Friday through Tuesday.

- A cold front will bring strong thunderstorms to the area on
  Saturday afternoon and evening.

- Thunderstorms capable of producing gusty outflow winds up to
  50 mph with areas of blowing dust.

&&

.SHORT TERM /Through Sunday Night/...
Issued 420 AM MDT FRI AUG 21 2026
A ridge will remain over the area with continued hot conditions.
A trough remains off the OR coast, bringing southerly flow to
the area over the next few days. Winds each afternoon will be
breezy south-southwest ahead of a cold front that arrives late
Saturday. Monsoon moisture will increase today to the 85 to
90th percentile through Saturday, with a 15-25 percent chance of
showers and thunderstorms. Increasing clouds late this
afternoon, which may lower temperatures a few degrees from the
forecast. Quite a bit of range in temperatures today with the
cloud cover uncertainty, with a few models showing up to 105
across the Snake Plain this afternoon under full sun. A cold
front will enhance shear aloft for the possibility of strong
organized thunderstorms on Saturday afternoon and evening. The
front will bring drier air to the area on Sunday with breezy
westerly winds. Temperatures will be around 10-15 degrees above
normal Friday, lowering to near normal by Sunday.

&&

.LONG TERM /Monday through Friday/...
Issued 420 AM MDT FRI AUG 21 2026
Southwest flow continues in the long term with monsoon moisture
keeping a threat of showers and storms over southwest ID. Models
show a potent shortwave moving over the area on Monday
afternoon with a 15 to 25 percent chance of showers and storms
over southwest ID. Forecast may need to be adjusted higher in
eastern OR for this shortwave. A trough off the Pac NW coast
pushes the monsoon moisture east on Tuesday with drier air,
breezy conditions and slightly cooler temperatures Tuesday
through Friday. Temperatures will around 2-5 degrees above
normal through the period.

&&

.AVIATION /12Z Friday through Saturday/...
Issued 624 AM MDT FRI AUG 21 2026
VFR. High density altitude this afternoon from heat. Areas of
wildfire smoke. Increasing clouds with isolated
showers/thunderstorms Friday evening through Saturday morning.
Surface winds: variable 5-10kt, showers and storms capable of
gusty erratic outflows up to 50 kt this evening. Winds aloft at
10kft MSL: SW-SE 15-25 kt.

KBOI...VFR. 10-20% chance of showers and thunderstorms over
terminal after Sat/00Z. Surface winds: variable 5-10kt, gusty
outflow winds 30-50kt possible this evening from the southwest-
southeast.

Weekend Outlook...Scattered showers and thunderstorms continuing
Saturday. Gusty outflow winds 30-45 kt and locally heavy rain from
storms. Drier Sunday. Areas of wildfire smoke. Gusty SW winds
Saturday afternoon. Breezy W-NW winds all areas on Sunday.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Heat Advisory until 9 PM MDT this evening for IDZ012-014-016-
     033.
OR...Heat Advisory until 9 PM MDT /8 PM PDT/ this evening for
     ORZ064.
     Fire Weather Watch from Saturday afternoon through Saturday
     evening for ORZ670>672.
&&

$$

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AVIATION.....KA
SHORT TERM...KA
LONG TERM....KA