691
FXUS65 KBOI 210627
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
1227 AM MDT Fri Aug 21 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 Sunday 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 /Monday through Friday/...
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 /06Z Friday through Saturday/...
Issued 1226 AM MDT FRI AUG 21 2026
VFR, with increasing mid-high clouds from the west. Patchy wildfire
smoke over east-central OR and west-central ID mountains overnight
through morning. Isolated showers/thunderstorms Friday evening
through Saturday morning. Storms capable of gusty outflows 30-40 kt.
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 overnight through morning. Isolated
showers/thunderstorms Friday evening, with a 15-20% chance over
terminal after Sat/00Z. Surface winds: light and diurnal under 7 kt
through Friday morning, becoming SW 6-11 kt in the
afternoon/evening.

Weekend Outlook...Scattered showers and thunderstorms continuing
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 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.....JY
SHORT TERM...LC
LONG TERM....JM