899
FXUS65 KBOI 051539
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
939 AM MDT Fri Sep 5 2025

.DISCUSSION...
The upper level ridge is still weakening, but today will be hot
and with persistent smoke through the area. AQI was 100-150 this
morning which indicates unhealthy conditions for sensitive
groups. This evening showers and storms are expected in Harney
and Malheur counties, with enough coverage to support a Red Flag
Warning for Burns BLM in Harney County for lightning and
outflows. Outflows could be as high as 50 mph, with considerable
areal coverage of outflows. A few models even carry outflows
into the Treasure Valley, though gusts will have weakened to a
maximum of 25 mph by the time they reach the valley around
9-11PM. The upper level trough supporting these storms is still
on track to swing through the area this weekend, continuing
storm chances through the weekend. We are continuing to watch
the progression of the low that`s carrying the trough through,
as when it moves inland next week it will drop max temperatures
to the 70s in lower elevations.

&&

.AVIATION...VFR and local MVFR with smoke layers. Scattered
showers and isolated thunderstorms in eastern OR this afternoon.
Outflow gusts could be as high as 45 kt. Surface winds:
variable 5-10kt, with gusts up to 20 kts in the Snake Plain this
afternoon. Winds aloft at 10kft MSL: variable 5-15kt.

KBOI...VFR with minor visibility reductions due to smoke
layers. Surface winds SE 5-15kt, shifting to NW 5-10kt late
afternoon through the evening.

Weekend Outlook...Scattered showers and thunderstorms on
Saturday afternoon. Gusty outflow winds up to 45kt possible.
Drier conditions on Sunday in eastern OR with lingering showers
and storms over ID mountains. Breezy southwest winds Sunday
afternoon, especially eastern OR and southwest ID highlands.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Sunday night...Upper level ridge
continues to weaken over the short term with a gradual cooling
trend. Isolated showers and thunderstorms this afternoon, mainly
across eastern OR. Showers and storms are capable of producing
outflow winds up to 40 mph this afternoon. An upper level
trough will approach the region from the west. The through will
remain off the northern CA coast on Saturday as a shortwave
moves inland. Precipitable water values reach the 80-85th
percentile on Saturday, or around 0.75 inch. The dynamics of
this trough will interact with the mid level moisture already in
place, with a 20-40 percent chance of thunderstorms across
eastern OR, and a 40-60 percent chance across southwest ID
highlands, and a 10-20 percent chance of thunderstorms north
and east of the Snake Plain. The upper level trough remains off
the northern CA coast. Strong southwest flow aloft arrives with
a dry slot developing over the area, with breezy west-
southwest winds during Sunday afternoon. Temperatures have
trended warmer on Saturday and Sunday as the upper level trough
remains offshore.

LONG TERM...Monday through Friday...The upper level trough
remains off the morthern CA coast on Monday, with southwest flow
aloft continuing and breezy conditions during the afternoon. The
trough is now forecast to move inland on Tuesdsay with cooler
conditions and a 20-30 percent chance of precipitation. Forecast
confidence beyond Wednesday is low with the handling of the
trough moving inland. Nonetheless, cooler conditions and a 20-40
percent chance of precipitation Wednesday and Thursday as the
trough moves inland. Temperatures lower around 10 degrees below
normal Wednesday through Friday.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...Red Flag Warning from 1 PM this afternoon to 9 PM PDT this
     evening ORZ670.

&&

$$

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DISCUSSION...JM
AVIATION.....JM
SHORT TERM...KA
LONG TERM....KA