964
FXUS65 KBOI 212011
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
211 PM MDT Tue Jul 21 2026

.KEY MESSAGES...
- Isolated to scattered showers and thunderstorms today, mainly
  over the higher terrain of the ID/NV border and west-central
  ID mountains.

- Shower/thunderstorm coverage and chances increase Wednesday
  with heavy rainfall possible, especially over the central
  Idaho mountains.

- Hot temperatures and areas of smoke through the week.

&&

.SHORT TERM /Through Thursday Night/...
Light rain / virga showers have been ongoing through the
morning into early afternoon, with some areas picking up a
couple hundreths. Southerly flow aloft will be maintained today
as the upper-level ridge remains in the south-central CONUS and
a low pressure system moves north along the Pacific NW coast.
Monsoonal moisture will continue to increase over the entire
area today, and even more on Wednesday. Precipitable water will
climb well over 1 inch, rising above the 95th percentile today
and closer to the 99th percentile on Wednesday, indicating a
very moist airmass. Instability this afternoon and evening will
be limited and focused over the higher terrain, where there is a
20-40% chance of showers and thunderstorms developing.
Thunderstorms may produce brief heavy rain and gusts 40-50 mph.
Showers and isolated thunderstorms will continue tonight near
the Nevada border as an impulse lifts north. The increasing
moisture and cloud cover will bring a few degrees of cooling
today in most areas compared to yesterday, but it will still be
hot. Similar to yesterday, smoke should decrease in the
afternoon as daytime heating mixes out smoke near the surface.
Outside of storms, winds will be locally breezy with gusts 15-25
mph. Northwest surface winds will transport smoke from
wildfires in Oregon back across the area tonight.

Southerly flow aloft will continue Wednesday, with a shortwave
trough expected to aid convection in the afternoon and evening
across the central Idaho mountains, where the chance of showers
and thunderstorms will rise to 40-90%. Deep moisture and
expected slow storm motion will result in the potential for
heavy rain and flash flooding, especially over burn scars and
steep terrain, including the Wapiti burn area. QPF totals near
the Wapiti have bullseyes of near 0.5" in 3 hours, and near
0.2" in 1 hour. A Flash Flood watch has been issued for the
Wapiti burn area from 12 pm MDT to 9 pm MDT Wednesday to match
the confidence for this threat. Models also indicate the
potential for gusty outflow winds as cold pools from
thunderstorms descend over the mountains, with wind gusts from
40-50 mph possible. Elsewhere, a 20-40% chance of showers and
thunderstorms will develop across the higher terrain with a less
than 20% chance in the lower elevations. Increased
clouds/showers will cool most areas slightly.

The upper-level low moving up the Pacific NW coast Tuesday and
Wednesday will begin to makes its way onshore Thursday, shifting the
flow aloft to southwesterly. This will begin to push monsoonal
moisture to the east, but there will still be enough moisture
and instability for a 10-20% chance of showers and
thunderstorms. Decreasing moisture will allow temperatures to
rise with lower valley highs once again near 100 degrees. Breezy
conditions will develop across southeast Oregon in response to
the southwest flow. Smoke may continue to impact the area
Wednesday and Thursday with improvement each afternoon.

&&

.LONG TERM /Friday through Tuesday/...
Friday looks very hot as the upper high over the Great Basin
builds to maximum amplitude while an upper trough stays off the
northwest coast.  High temps will reach 102 to 106 degrees in the
Treasure Valley and southern Malheur County, with 90s in the
mountains as high as 5000 feet.  By then most of the monsoon
moisture will be east of our CWA but eastern Owyhee County and
Twin Falls County will still be in it with a slight chance of
thunderstorms.  On Saturday, upper winds will become more westerly
as part of the offshore trough comes inland.  This means slightly
cooler temps although still hot, but also drier.  Hot, dry weather
will continue through Tuesday.

&&

.AVIATION /18Z Tuesday through Wednesday/...
Issued 1132 AM MDT TUE JUL 21 2026
Generally VFR. Areas MVFR- IFR visibility due to wildfire
smoke, gradually improving this afternoon and evening.
Broken clouds AOA 15 kft MSL. Scattered showers and isolated
thunderstorms near the NV border and in the central ID mountains.
High density altitude during afternoon heat. Broken clouds AOA
12 kft MSL increasing from the south after 22/00Z.  After 22/06Z
scattered showers and thunderstorms near the NV/ID border with
brief heavy rain and outflow winds to 40 kt. Surface winds:
W-NW 5-15 kt with local gusts around 25 kt. Winds aloft at 10kft
MSL: NW around 10 kt.

KBOI...VFR. Broken clouds AOA 15 kft MSL until 20Z then decreasing
to scattered. High density altitude during afternoon heat.
Surface winds: NW 5-10kt until 21Z, then NW 10-15 kt with gusts
20-25 kt until 22/01Z. Broken-overcast clouds AOA 15 kft spreading
in from the south after 22/05Z.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Air Quality Alert until 3 PM MDT Wednesday for IDZ011-012-014-
     033.
     Flash Flood Watch from Wednesday afternoon through Wednesday
     evening for IDZ013.
OR...Air Quality Alert until 1 PM MDT /noon PDT/ Wednesday for
     ORZ061>064.
&&

$$

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SHORT TERM...CH
LONG TERM....LC
AVIATION.....LC