465
FXUS65 KBOI 171120
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
520 AM MDT Mon Aug 17 2026

.UPDATE...Updated aviation discussion.

&&

.KEY MESSAGES...
- Isolated showers and thunderstorms this afternoon favoring
  higher terrain, with outflows up to 35 mph and brief
  downpours.

- Temperatures near or slightly above normal through mid-week,
  then heat amplifying for Thursday and Friday.

- Return of monsoon moisture Friday into the weekend will
  increase shower and thunderstorm chances once again.

&&

.SHORT TERM /Through Wednesday Night/...
Issued 235 AM MDT MON AUG 17 2026
A desert-southwest ridge will remain amplified over the region
today as a Pacific trough sits offshore, placing E Oregon and
SW Idaho under southwest flow aloft. Pacific moisture is also
streaming across the area in this southwest flow, creating
mostly cloudy skies with warmer morning temperatures. A weak
shortwave disturbance will arrive today and combine with the
Pacific moisture/daytime instability to generate isolated
showers and thunderstorms this afternoon. The shower activity is
mainly expected across northeast Oregon, and central/south-
central Idaho, throughout the afternoon to late evening. Storm
outflows to around 30-35 mph will be possible.

An upper trough will move along the Canadian border on Tuesday,
briefly flattening the ridge and shifting mid/upper flow to
westerly. This will introduce drier air from the west, nudging
shower/thunderstorm activity east of the area on Tuesday. The
exception will be across central Idaho where lingering moisture
will support a slight chance of afternoon storm development. The
ridge will quickly rebound by Wednesday, with dry conditions
continuing. Max temperatures will be within a few degrees of
normal through Wednesday.

&&

.LONG TERM /Thursday through Monday/...
Issued 235 AM MDT MON AUG 17 2026
The aforementioned upper ridge will further amplify on Thursday
and Friday as the Pacific trough approaches the west coast and
enhances southerly flow. This pattern will bring back summertime
heat risk, with temperatures climbing to near 100 degrees for
lower elevations. The trough will begin to track northeast into
the PacNW on Friday and Saturday, pulling monsoonal moisture
back into the region from the established southerly flow aloft.
Shower and thunderstorm chances will be re-introduced Fri/Sat
afternoons with winds becoming breezier. The proximity of the
trough will help to lower temperatures back to near-normal
Saturday, and into Sunday. The trough will continue northeast
into Canada on Sunday, pulling in drier conditions for the
northwest/west zones while monsoon moisture remains over
portions of central Idaho through at least Monday.

&&

.AVIATION /12Z Monday through Tuesday/...
Issued 515 AM MDT MON AUG 17 2026

Generally VFR. Weak, isolated showers and thunderstorms this
afternoon/eve across NE Oregon and s-central/central Idaho,
including KTWF-KJER. Erratic outflows to around 30 kt possible.
Patchy surface smoke near KBKE/KBNO. Surface winds: variable up
to 10 kt, becoming SW-NW 5-15 kt this afternoon. Winds aloft at
10kft MSL: SW 5-15 kt.

KBOI...VFR. Weak, isolated showers and thunderstorms in SW
Idaho this PM, with a 10% chance of hitting KBOI. Possible storm
outflows around 20-30 kt in Treasure Valley. Surface winds:
variable or SE around 6 kt, shifting to NW-N 5-10 kt in the
afternoon.

&&

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

OR...None.

&&

$$

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AVIATION.....SH
SHORT TERM...SH
LONG TERM....SH