553
FXUS65 KBOI 181743
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
1143 AM MDT Fri Sep 18 2026

.UPDATE...Updated aviation discussion.

&&

.KEY MESSAGES...
- Showers, scattered thunderstorms, and cooler temperatures
  today.

- Strongest thunderstorms in central Idaho with gusty outflow
  winds, hail, and brief heavy rain.

- Gradual warming and drying trend beginning Saturday and
  continuing through early next week.

&&

.SHORT TERM /Through Sunday Night/...
Issued 258 AM MDT FRI SEP 18 2026
The center of the low pressure system bringing storms and
showers to Southern Idaho moves overhead today. This will again
support convection this morning through Friday night with
showers across the area and scattered thunderstorms this
afternoon and evening. Thunderstorms will be capable of
producing gusty winds up to 50 mph, small hail, and brief heavy
rain. Abundant lightning is also likely, and fast storm motion
will keep rainfall amounts low. Inside the center of the low,
temperatures cool down 5-10 degrees from Thursday. While
thunderstorm activity wanes Friday night, showers continue
through Saturday morning as moisture wraps around the eastward
low pressure center. A chance of precipitation remains in the
higher terrain of Central Idaho through Saturday evening. Behind
the low, high pressure returns as a ridge axis moves over the
region, leading to warming conditions late Saturday and through
Sunday. Temperatures warm up to about 5 degrees above normal by
Sunday.

&&

.LONG TERM /Monday through Friday/...
Issued 258 AM MDT FRI SEP 18 2026
With models slightly out of phase later in the long term, and
the only chance of precipitation associated with a weak low over
Southern California, the bulk of the long term forecast is
focused on temperature trends as the synoptic pattern shifts.
Monday afternoon through Tuesday evening, the weak Californian
low moves across the Southwestern US. During this time, we
occupy a slightly moistened northeastern quadrant between the
low and zonal flow to our north. Dynamics will favor development
of showers in Central and Eastern Idaho Monday and Tuesday
afternoons. The chance of precipitation each afternoon is only
10%. Otherwise, that zonal flow to the north moderates
temperatures, holding them steady at 5 degrees above normal for
most of the long term. Slight warming on Thursday is expected as
high pressure builds ahead of a strong Alaskan low pressure
system. This low pressure system moves through British Columbia
late next week, with model variation on the exact track keeping
our forecast low confidence that far out.

&&

.AVIATION /18Z Friday through Saturday/...
Issued 1138 AM MDT FRI SEP 18 2026
VFR in eastern Oregon. Mainly VFR in southwest Idaho with
occasional MVFR through early Sat/AM amidst scattered to
widespread showers and isolated thunderstorms. Storms this
afternoon could produce outflows gusts up to 35 kt. Surface
winds outside of storms: W-NW 5-15 kt with gusts to 20-25 kt
Fri/PM. Winds aloft at 10kft MSL: NW-N 5-15 kt.

KBOI...Mainly VFR. Showers developing N and E of KBOI this
afternoon. Highest chances for showers over terminal will be
late Fri evening, with brief MVFR possible. 10% chance of
lightning at the terminal. Clearing early Sat morning with SCT
clouds and light winds. Surface winds: NW 5-15 kt.

Weekend Outlook...Brief MVFR and mountain obscuration in lingering
showers near KTWF-KJER on Saturday, with showers tapering off by
midday. Expect VFR conditions otherwise through Sunday with variable
winds less than 10 kt overnight and in high terrain and NW 5-15 kt
in valleys during the afternoon.
&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Flash Flood Watch through this evening for IDZ013-028.
OR...None.

&&

$$

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AVIATION.....JR
SHORT TERM...JM
LONG TERM....JM