Mesa, Idaho Weather Forecast Discussion

279
FXUS65 KBOI 020259
AFDBOI
Area Forecast Discussion
National Weather Service Boise ID
859 PM MDT Wed Oct 1 2025
.DISCUSSION...An upper level trough remains off the Pacific NW
coast with isolated showers embedded in the southwest flow
aloft. The upper level trough will transition into northern CA
by Thursday afternoon into Friday. A deformation band will set
up over southwest Idaho and bring widespread precipitation on
Friday morning, with moderate to heavy amounts over the west
central ID and Boise mountains. A flash flood watch remains in
effect for the Wapiti Burn Scar for moderate to heavy
precipitation amounts potentially causing debris flows around
Idaho Highway 21. Current forecast on track with no updates.
&&
.AVIATION...Isolated showers/thunderstorms will become widespread
across E Oregon and SW Idaho by Thursday late afternoon. MVFR/IFR
and localized LIFR in moderate/heavy precip. Mtns obscured. Surface
winds: variable 5-10 kt. Winds aloft at 10kft MSL: SW 15-30 kt.
KBOI...VFR. Brief light rain showers ending this evening. Showers
returning 02/23Z, and will become continuous Thu night. Periods of
MVFR/IFR in moderate/heavy rain Thu night. Surface winds: SE 5-10 kt
becoming variable 3-6 kt after 02/09Z.
&&
.PREV DISCUSSION...
SHORT TERM...Tonight through Friday night...Light rain showers are
occurring over the Owyhee Mountains this afternoon, with
increasing clouds thanks to moist southwest flow over the
region. Temperatures will continue to cool through the rest of
the week, with another push of cold air thanks to a deep upper
level low off the coast of British Columbia. This low will
deepen over the West Coast, sending a cold front through the
Intermountain West tomorrow afternoon. This will bring
widespread rainfall, with a band of particularly heavy
precipitation lingering from the Owyhee Mountains up through the
West Central Mountains. This band looks to persist through
Friday morning as the low deepens to our south. Rainfall totals
by Friday afternoon will range from 0.25 to 0.50 with showers
outside of the band with up to an additional 1.5 inches of rain
inside the heavier band of precipitation. This additional heavy
rainfall will bring a risk of flash flooding to area burn scars
and steep and rocky terrain, so we have issued a flash flood
watch for the Boise Mountain and West Central Mountains.
Instability remains limited over much of the area, but there is
a 10-20% chance of thunderstorms with the initial cold frontal
passage tomorrow afternoon.
Much cooler temperatures along with breezy westerly winds will
continue through the Friday evening, with clearing over southeast
Oregon by Friday afternoon. Southwest Idaho will see lingering
showers over high terrain through early Saturday morning.
LONG TERM...Saturday through Wednesday... Strong northwesterly
winds will follow the trough that brought us the weather in the
short-term. A notable surface pressure gradient combined with low-
level flow roughly oriented with the Snake Plain, so have opted
to blend in a little bit of the NBM 90th percentile winds
Saturday afternoon/evening. This will allow for wind gusts of
25-35 mph throughout the Snake Plain, with isolated gusts of 40
mph. Winds will remain breezy on Sunday, although lower than
Saturday. The evolution of the upper-level flow will feature a
shortwave crossing over our area Late Saturday into Sunday,
before breaking off in a low over California. The initial
passage of the shortwave will allow for a 15-35% chance of
precipitation across the Central Idaho Mountains. With snow
levels to dropping to 6500-7500 ft, this will allow for some
snow/wintery mix on the highest peaks (although little to no
accumulation is expected). Beyond Saturday, our forecast is
looking to be mostly dry as the ensemble consensus shows a Rex
Block sets in with a ridge building north/northwest of the
California Low. While we are not in the favorable location to
receive precipitation from the California low, isolated showers
can`t be ruled out. Multi-run model ensembles continue to hint
at trace amounts of precipitation here and there. For now, how
kept the chance of precipitation 

NWS BOI Office Area Forecast Discussion