East Mountain Way, Idaho Weather Forecast Discussion

794
FXUS65 KBOI 271606
AFDBOI
Area Forecast Discussion
National Weather Service Boise ID
1006 AM MDT Sat Sep 27 2025
.DISCUSSION...Latest models continue to highlight the big
weather change Monday as a strong Pacific cold front comes in,
supported by a deep upper trough in the Gulf of Alaska. After
sunny, warm weather today and Sunday with high temps in the
70s to mid 80s, temperatures will lower about 15 degrees
Monday, with widespread rain moving in with the cold front.
Latest time or arrival of the cold front looks delayed a few
hours from previous forecasts but all the weather will still
be there: Total rainfall Monday through Wednesday around .50
inch in the Snake Basin to 1.00-1.50 inch in the Idaho
mountains, heaviest in the Boise Mountains, and .20 to .50
inch in eastern Oregon. Southwest flow aloft will help increase
rainfall on the Idaho side, with relatively less in Oregon.
Latest models also have a reinforcement of the upper trough in
the Gulf of Alaska on Wednesday which could increase rain in
our CWA Wednesday and last through Friday, while also keeping
temperatures below normal all week. Current forecast covers
these features already. Will include new details to the
afternoon package.
&&
.AVIATION...VFR with clear skies. Surface winds: variable and
E-SE 5- 10 kt. Winds aloft at 10kft MSL: Variable 5-10 kt.
KBOI...VFR with clear skies. Surface winds: SE up to 10 kt
through morning and early afternoon.
Sunday Outlook...VFR. Slight chance of showers/thunderstorms in
S-central Idaho Sunday afternoon and evening. Storms capable of
localized outflows up to 30 kt. Increasing mid/high-level clouds
Sunday. Surface winds: SE-SW 10-20kt through Sunday. Winds aloft
at 10kft MSL: 15-25 kt through Sunday.
&&
.PREV DISCUSSION...
SHORT TERM...Today through Monday night...Warm, dry, and clear
today through Sunday afternoon as we sit in the high pressure
saddle between a closed low over SoCal and an encroaching
Alaskan low. Temps warm to about 10 degrees above normal Sunday.
Sunday evening, the deep Alaskan low brings increased cloud
cover and steadily increasing chances of precipitation. Sunday
evening and night precip chances are 15-25%, with forcing
provided by the SoCal low becoming entrenched in the Alaskan
low`s jet stream. As heights gradually fall, temps fall closer
to what is climatologically normal for this time of year, with
Monday`s high temps being in the low 70s for lower elevations
and low 60s for mountain valleys. Monday afternoon and evening
precip chances increase drastically to 60-80% across the area.
While colder surface temps and cloud cover may inhibit
instability, thunderstorms are possible in orographically
induced convection, with a 20-30% chance of thunder across the
area. The abundant atmospheric moisture is forecast to produce
0.2-0.5 inches of rain in lower elevations, and 0.5-1 inch of
rain in higher elevations through Monday. Strong southwesterly
flow aloft may shadow valley locations, including the Treasure
valley, but the chances of receiving a tenth of an inch of
rainfall there is still 50%. The strong jet will mix down to
ridges and highlands, resulting in some localized 20-30 mph
gusts. Precipitation and cooling temperatures continue into the
long term.
LONG TERM...Tuesday through Saturday...Cooler, unsettled weather
continues into the long term. A deep closed upper-level low,
resembling what would be a late fall/winter system, will slowly
make its way over our area. As this low approaches, embedded
short waves may act to locally enhance the dynamics of this
system and bring addition periods of precipitation. Models are
in generally good agreement on a short wave and surface cold
front pushing through the area on Tuesday. Although with strong
mid-level flow oriented out of the southwest, some shadowing
effects are possible. The highest chances of precipitation
Tuesday afternoon will be found in the Central Idaho Mountains,
ranging from 60-70%. Despite ample cloud cover and cooler
surface temperatures, the cooling temperatures aloft and added
dynamics of the trough will allow for enough instability to
support a slight chance of thunderstorms across southwest Idaho
come Tuesday afternoon. Periods of precipitation are expected
through Friday as our area continues to remain under the
influence of this trough. However, we will begin to dry out by
Saturday as it finally pushes off to the east. Temperatures
will hover 5-10 degrees below normal throughout the long term.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.
&&
$$
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DISCUSSION...LC
AVIATION.....JY
SHORT TERM...JM
LONG TERM....NF

NWS BOI Office Area Forecast Discussion