598
FXUS65 KBOI 300922
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
322 AM MDT Tue Sep 30 2025

.SHORT TERM...Today through Thursday night...The front and
accompanying precipitation is exiting to the east this morning,
leaving a wide swath of 0.50-1" amounts across SW Idaho, with
lesser amounts (mostly around 0.10 but up to 0.25") across SE
Oregon. For today the focus of precipitation will be over the
mtns of SW Idaho as afternoon instability feeds scattered shower
and thunderstorm development. Southwest flow aloft will direct
showers/storms to the northeast, bringing activity into the
Snake Plain during the afternoon. Slightly more stable
conditions will likely cap development over SE Oregon today
with a 15-25% chance of showers/storms limited to Baker County.
The flow aloft will bring breezy winds to SE Oregon and higher
terrain of SW Idaho with gusts of 25 to 35 mph this afternoon.
The chance of showers continues Wednesday with better dynamic
forcing expanding coverage, especially across SE Oregon.

The main trough and accompanying front push onto the Pac NW
coast on Thursday with showers focused in the mountains.
It`s looking more likely that a band of precipitation will form
along the front late Thursday as it briefly stalls across
northern NV and s-central Idaho Thursday night. Forcing along
the slow moving front coupled with precipitable water amounts
around one inch could lead to moderate precipitation across the
western Magic Valley and higher terrain near the ID/NV border
Thursday night into Friday. Temperatures through Thursday are
near normal or slightly below normal.

.LONG TERM...Friday through Tuesday...An upper low amplifies as
it moves into the Pacific Northwest, providing a very strong
moisture flow in far SW and S-central Idaho Friday morning
through the afternoon. The Magic Valley is still expected to be
directly under the precipitation from the flow, and by the end
of Friday will have 0.25" to 0.5" of rainfall. Given how narrow
the band is, there is a degree of uncertainty in the forecast if
the models shift even slightly. A slight chance of showers
continues through s-central and central Idaho through Friday
evening. Friday night the low moves east and mostly dry
northerly flow streams over the region. Another wave is set to
amplify Sunday night, just clipping central Idaho with enough
moisture for another round of isolated showers. Deterministic
models agree on closing this wave off over central California,
putting us in the dry deformation zone of the pattern. However,
model agreement quickly breaks down after Monday. Temps cool
from Friday to Sunday, with temps Sunday being 10 degrees below
normal. Monday and Tuesday the forecast warms slightly in the
deformation zone.

&&

.AVIATION...The very moist cold front is moving out of area in s-
central ID around Tue/11Z. Thunderstorm chances have diminished this
morning, but widespread showers remain. Isolated storms possible in
the W-central Mtns of ID later this morning, and developing across
the rest of Idaho by Tue/20Z. Light afternoon showers develop in SE
OR at the same time. Low certainty in fog or stratus formation
tonight behind the front, but MVFR-LIFR is possible in the rain
band. Surface winds: SW-SE 5-15 kt, becoming 15-25 kt in highlands
this afternoon. Winds at 10kft MSL: SW 15-25 kt.

KBOI...VFR likely, with low certainty in low stratus development
this morning. Isolated showers and storms develop this afternoon in
the area, capable of producing gusts up to 30kt. Winds remain out
of SE at 5-10 kt this morning, becoming 10-15 kt this afternoon.

&&

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

&&

$$

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SHORT TERM...DG
LONG TERM....JM
AVIATION.....JM