Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 222011
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
211 PM MDT Fri Mar 22 2024

.SHORT TERM...Tonight through Sunday night...The afternoon and
evening will see an increase in cloud cover due to a weakening
upper-level ridge. This is in anticipation of an approaching
upper-level low, which is expected to bring precipitation on
Saturday. With the exception of a few showers expected to
develop later this afternoon over south-central Idaho, warm and
mostly dry conditions will persist.


Satellite imagery reveals a well-developed low-pressure system
off the southwestern Oregon coast this afternoon, which will
push a cold front through the forecast area on Saturday morning.
Showers will develop ahead of the cold front after midnight
tonight, with the bulk of the precipitation arriving just ahead
of the front. The cold front is anticipated to reach Burns at
approximately 2 AM MST, Ontario at approximately 6 AM, Boise at
approximately 9 AM, and Twin Falls at approximately 11 AM. The
snow level will initially be around 6,000 feet tonight and
gradually descend to around 5,000 feet by Saturday afternoon.
Wet snow accumulation is expected above 5,500 feet, with up to 2
inches forecast. Below 5,500 feet, there is a 90% probability
of receiving less than half an inch of moisture. The lower
valleys will experience rain, with a 60% probability of
receiving more than 0.10 inches of total rainfall. The upper-
level trough will move over the region on Saturday afternoon,
fostering the development of convective showers. A slight
likelihood of thunderstorms has been added to the forecast, with
afternoon CAPE values reaching 150 J/KG.

As the trough continues east, a cold northerly flow will follow
on Sunday. This will result in temperatures returning to a few
degrees above normal. Throughout the day, showers will persist,
with most of the guidance indicating the passage of an embedded
shortwave on Sunday night. This would increase the likelihood of
precipitation, particularly across southwest Idaho, from Sunday
night into early Monday. Additionally, this would strengthen the
surface pressure gradient across the Western Snake River Plain,
resulting in gusty northwesterly winds Sunday afternoon. The
most recent NBM guidance indicates a 70% probability of gusts
exceeding 41 knots at Twin Falls and Jerome. However, the ECMWF
Extreme Forecast Index (EFI) does not indicate any wind
deviation for Sunday, which is based on reforecasts from
2003-2024. From Saturday night to Sunday night, snow levels will
decrease from 5,500 feet to 4,500 feet. This could result in a
light additional snowfall in the mountains.

.LONG TERM...Monday through Saturday...An unsettled wet and
cool pattern will remain in place through the long term period.
Northwesterly upper level flow will bring seasonable
temperatures and intermittent light precipitation to the region
on Monday and Tuesday. A weak ridge will build in late Tuesday
through Wednesday, bringing a brief period of drier conditions.
A deep low pressure system moves in Wednesday evening, bringing
more precipitation on Thursday. Precipitation lingers through
the rest of the long term as the low comes inland. Snow levels
stay roughly at 3500-5000 ft MSL during precipitation events. In
the lower Snake Plain, there is a <5% chance for mixed wintry
precipitation Monday morning when snow levels are lowest. The
rest of the period temps stay moderated, with little change.
Monday/Tuesday snowfall in the higher elevations is light, 0-2",
increasing during the Thursday/Friday event to 1-4" in mtn
valleys and 6-10" on ridges. In lower valleys where
precipitation will be mostly rain, 0.1-0.3" of rainfall are
expected through the period. Winds increase ahead of the deep
low, with gusts up to 30 kts forecast on Wednesday and Thursday
afternoons.

&&

.AVIATION...Mainly VFR and dry with mid and upper level clouds.
Isolated showers in the Magic Valley tonight. Widespread rain/snow
Saturday morning and obscured mountains as a cold front moves in.
VFR/MVFR in rain showers, and MVFR/IFR in snow showers. Snow levels
6-7 kft MSL. After a brief pause in precip around noon,
afternoon/evening scattered showers and isolated thunderstorms
develop. Surface winds: S-SE 5-15 kt, with gusts 20-30 kt developing
this afternoon across SE OR. Winds aloft at 10kft MSL: S-SW 20-35
kt, up to 50 kts along the cold front.

Sunday Outlook...Showers will continue into Sunday, with snow levels
dropping to 4-5 kft MSL behind the front. Surface winds SW-NW 10-20
kt Saturday into Sunday. Winds generally strongest each afternoon,
with gusts to 30 kt in the higher elevations and across s-central
ID, but widespread on Sunday.

&&

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

&&

$$

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SHORT TERM...JDS
LONG TERM....JM
AVIATION.....JM


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