205
FXUS65 KBOI 090242
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
842 PM MDT Mon Sep 8 2025

.DISCUSSION...At 8 PM MDT satellite imagery showed an upper low
just off the Calif coast near Crescent City. A lobe of showers
and thunderstorms extended from the low to northeast OR (north
of Baker County), and was pivoting away from our CWA. Our CWA
should remain dry through the night, although clouds will
increase in Harney County as the low center edges inland.
Further eastward progress of the low will be slow, and showers/
thunderstorms in our area Tuesday will be mainly due to
destabilization, while stratiform rain closer to the low center
gradually spreads eastward across Oregon. Hi-res models predict
an area of showers/storms over the central ID mountains late
Tuesday, already in our forecast. We also have a 20-40 percent
chance of showers and thunderstorms in northern Harney and
western Baker Counties late Tuesday. Significant cooling along
with more numerous showers or even steady rain will come in
Wednesday through Friday as the upper low finally reaches Idaho.
No updates.

&&

.AVIATION...VFR. Isolated showers and thunderstorms possible
for areas north of the Snake Plain overnight, otherwise partly
cloudy. SFC winds variable 5-15 kt. Winds aloft at 10kft MSL:
SW 5-15 kt.

KBOI...VFR with some mid level clouds overnight. Winds become
SE less than 10 kt, before turning to the northwest Tuesday
afternoon. VFR to continue Tuesday.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Wednesday night...A slow moving
closed low will increase the chance of precipitation, including
afternoon thunderstorms, as it tracks across Oregon Tuesday and
Wednesday. On Tuesday, the focus of development will be across
higher terrain in the w-central Idaho mtns while a dry slot to
the west minimizes development across SE Oregon. By Wednesday
afternoon the mid-level circulation is expected to reach SE
Oregon. Showers and thunderstorms will continue to precede the
low center, developing across s-central ID and the w-central
ID mtns while an area of precipitation sets up under the low
center across SE Oregon (Harney/Malheur counties). Precipitable
water values reach 0.75-1" by Wednesday, increasing potential
for locally heavy rainfall (as outlined by the Marginal Risk in
WPC`s Excessive Rainfall Outlook). Across portions of SW Idaho
these amounts could come quickly from thunderstorms, while a
period of steady moderate to locally heavy rainfall and embedded
thunderstorms would add up on a longer timescale in SE Oregon
zones. While the thunderstorm environment is looking favorable
across SW Idaho from the west-central Idaho mtns through the
Treasure Valley and western Magic Valley to the ID/NV line it is
highly dependent on the timing/track of the closed low and
accompanying cloud cover so uncertainty remains. Temperatures
are near normal on Tuesday (low 80s in the valleys), dropping to
5-10 degrees below normal on Wednesday.

LONG TERM...Thursday through Monday...The upper low/trough will
be slow to move across the area Thursday and Friday.
Precipitation chances are fairly high (40-70 percent) Thursday,
then decrease on Friday (30-60 percent). Thunderstorm chances
are about 15-20 percent each day. Drier and a little warmer
conditions on Saturday in between systems. Models bring another
trough through the area on Sunday and Monday with slightly
cooler temperatures and a chance (20- 40 percent) of
precipitation. Temperatures will be around 10 degrees below
normal on Thursday and Friday, warming to near normal by
Saturday, then 2-5 degrees below normal Sunday and Monday.

&&

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

&&

$$

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DISCUSSION...LC
AVIATION.....MC
SHORT TERM...DG
LONG TERM....TL