474
FXUS65 KBOI 202356
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
556 PM MDT Thu Aug 20 2026

.UPDATE...Updated aviation discussion.

&&

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

- Increased chance of afternoon and evening showers and
  thunderstorms over higher terrain Friday through Sunday.

- Above normal temperatures next week with a chance of afternoon
  thunderstorms over southwest Idaho Monday and Tuesday.

&&

.SHORT TERM /Through Saturday Night/...
Issued 213 PM MDT THU AUG 20 2026
The Heat Advisory for the Treasure Valley, western Magic Valley,
and Upper Weiser River Valley will continue through Friday as a
high-amplitude upper ridge holds strong over the Four Corners
region. Models bring monsoon moisture northward through NV
Friday leading to a 15-25 percent chance of high-based
thunderstorms on the Idaho side late Friday through Saturday.
These storms would bring gusty winds but little rain. Meanwhile,
satellite shows high clouds streaming into our CWA from the
Pacific subtropics guided by an upper trough off the west coast.
These clouds won`t bring rain but they should lower Friday
afternoon`s temperatures a few degrees. Without the clouds the
lower valleys would get close to 105 degrees, and a couple of
models actually show that. On Saturday, deeper monsoon moisture
from the south will allow thunderstorms to be more effective
rain-producers, while continuing cloudiness and the approach of
a weak surface cold front and the coastal upper trough should
lower temps 5 to 10 degrees from Friday`s highs.

&&

.LONG TERM /Sunday through Thursday/...
Issued 213 PM MDT THU AUG 20 2026
Sunday will be a bit cooler than Saturday, but still warm or hot
across the region, with relative humidities still very low in the
drier airmass. Frontal winds on Sunday move into central Idaho,
bringing 20 to 30 mph wind gusts to higher terrain in the afternoon.
Winds return to normal strength through the rest of next week.
As the upper ridge builds back in following the front and trough,
temperatures slowly climb into next week, but hold steady around
normal to a few degrees above normal for this time of year. The
building ridge also allows for monsoonal moisture to continue
to stream into the region, leading to a daily slight chance of
showers and storms in s-central Idaho and central Idaho.

&&

.AVIATION /00Z Friday through Saturday/...
Issued 548 PM MDT THU AUG 20 2026
VFR, with increasing mid-high clouds from the west. Patchy
wildfire smoke over east-central OR and west-central ID
mountains this evening through overnight. High density altitude
from heat through sunset. Surface winds:
SW-NW 5-15 kt until 21/02Z then generally variable and diurnal
less than 8 kt tonight through Friday morning. Winds aloft at
10kft MSL: SW 15-25 kt.

KBOI...VFR, with SCT-BKN high clouds. Patchy wildfire smoke may
slightly obscure foothills tonight. Surface winds: NW 5-10 kt
this evening, becoming light and diurnal under 7 kt late
tonight through Friday morning.

Weekend Outlook...Scattered showers and thunderstorms late
Friday through Saturday. Gusty outflow winds 30-45 kt and
locally heavy rain from storms. Drier Sunday. Local reductions
in visibility due to wildfire smoke through the weekend. Gusty
SW winds Saturday across SE Oregon. Breezy W-NW winds all areas
on Sunday.

&&

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

$$

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AVIATION.....JY
SHORT TERM...LC
LONG TERM....JM