412
FXUS65 KBOI 182342
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
542 PM MDT Sat Jul 18 2026

.UPDATE...Updated aviation discussion.

&&

.KEY MESSAGES...
- Showers/thunderstorms across south-central Idaho and the
  central Idaho mountains this afternoon.

- Areas of smoke in southeast Oregon, drifting into southwest
  Idaho through the week.

- Hot temperatures through this week, hottest on Monday.

- Showers/thunderstorms increase next week with heavy rainfall
  possible Tuesday through Friday.

&&

.SHORT TERM /Through Monday Night/...
Issued 216 PM MDT SAT JUL 18 2026
A trough in British Columbia will flatten the prevailing ridge
over the region today, creating a favorable atmosphere for
thunderstorms and showers in central, south-central, and
southeastern Idaho. Isolated to scattered shower and storm
development in our area will be confined to the eastern portions
of the Boise and West Central Mountains, and especially near the
Magic Valley and ID-NV border region. Thunderstorms will be
capable of 30-50 mph outflow gusts, small hail, and heavy rain.
As the BC trough moves north of the region overnight, the
moisture stream momentarily moves east out of the area for
Sunday. Temperatures today and Sunday remain hot with valley
highs in the upper 90s to around 100 degrees.

Monday as the high pressure moves further west, we again begin
to move into a monsoonal pattern. Before the moisture arrives,
the strong southerly flow warms temperatures up even more.
Monday is currently forecast to be the hottest day in the
forecast, with lower elevations seeing highs 100 to 105 degrees.
That afternoon and evening, storms in Utah and Nevada creep
just up to the ID-NV border. They may stray as far north as the
Magic Valley that evening. Outside of storms, mild breezes are
expected each day with gusts 15-30 mph. Westerly and
northwesterly surface winds will continue to transport smoke
from Oregon fires into southeast Oregon and across southwest
Idaho into early next week.

&&

.LONG TERM /Tuesday through Saturday/...
Issued 216 PM MDT SAT JUL 18 2026
The upper-level ridge centered over the south-central U.S. will
remain through the extended. On Tuesday and Wednesday, continued
southerly flow aloft will transport monsoonal moisture into the
area. Ensemble-mean precipitable water values increase to around
1.25 inches, or above the 95th percentile. Shower / afternoon
thunderstorm chances increase to 20-50% across the higher terrain on
Tuesday, then across all areas Wednesday and Thursday as
deterministic models hint at shortwave impulses aiding development.
The deep moisture and potential for slower storm motion will result
in heavy rain and flooding concerns through much of the week. Flow
aloft will be affected by an upper-level trough moving onshore into
the Pacific NW during the end of the work week into the weekend.
This will shift flow aloft to more southwesterly than southerly,
which will begin to push the moisture to the east, with
precipitation chances gradually decreasing in our western zones. The
ridge will keep temperatures hot through the period, averaging a few
degrees above normal. Afternoon wind gusts Friday onwards will
increase with the upper-level trough increasing the pressure
gradient. Smoke will likely continue to impact much of the area
through the week, especially across southeast Oregon.

&&

.AVIATION /00Z Sunday through Monday/...
Issued 542 PM MDT SAT JUL 18 2026

Mainly VFR. Wildfire smoke reducing visibility in SE Oregon,
expanding into SW Idaho tonight. Greatest visibility reductions
in Oregon with MVFR/IFR conditions. Visibility will increase
Sun/PM. Isolated showers and thunderstorms over Central and
S-Central Idaho this evening capable of gusty outflows.
Afternoon high density altitude due to heat through the weekend.
Surface winds: SW-NW 5-12 kt. Localized gusts 15-25 kt late
this afternoon/evening. Then generally variable up to 8 kt
overnight. Winds aloft at 10kft MSL: W-SW 5-15 kt.

KBOI...VFR with some haze due to wildfire smoke. Afternoon high
density altitude through the weekend. Surface winds: NW 8-14 kt
with gusts up to 24 kt this evening, then light and variable
overnight.

&&

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

OR...Air Quality Alert until noon PDT Monday for ORZ061-062.
&&

$$

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AVIATION.....NF
SHORT TERM...JM
LONG TERM....CH