Area Forecast Discussion
Issued by NWS Boise, ID

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000
FXUS65 KBOI 260302
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
902 PM MDT Mon Mar 25 2024

.DISCUSSION...Scattered showers will continue overnight as cold
unstable air aloft remains over the region. These showers will
continue into Tuesday afternoon, with a slight chance of
thunderstorms during the afternoon hours during peak heating. A
weak ridge axis will transition over the area on Wednesday
bringing drier and warmer conditions. Then a cold front will
arrive on Thursday bringing widespread precipitation and
lowering snow levels. Forecast on track with no updates.

&&

.AVIATION...Mostly VFR. Scattered snow and rain showers through
Tuesday evening. Snow levels 3500-4500 feet. Mountains obscured in
precipitation and low clouds. Low confidence in patchy mountain
valley fog early Tuesday morning. Surface winds: W-NW 5-10 kt except
W-NW 15-20 kt with gusts to 30 kt in the Magic Valley. Variable
overnight in the W-Central Mtns. Winds aloft at 10kft MSL: NW 15-25
kt.


&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Wednesday night...Scattered light
showers are expected to persist across much of the area until
late tonight. These showers are primarily driven by surface
heating, coupled with the presence of cold air aloft and weak
dynamics associated with the trailing edge of the upper-level
trough. Rain accumulation from these showers this afternoon is
anticipated to be minimal. Although instability remains weak,
there is only a 3% chance of lightning this afternoon. However,
some of the stronger showers may produce graupel or snowfall
below 5000 feet.

High-resolution models indicate the passage of a weak
shortwave, observed near 46 North and 145 West at 2 PM, later
this evening. This will likely intensify shower activity across
southeastern Oregon. As the shortwave progresses southeastward,
it will extend the threat for showers into southwest Idaho by
Tuesday morning. With the snow level around 3500 feet MSL,
precipitation is expected to remain as rain in the valley.
Showers are forecasted to taper off by Tuesday afternoon.

By late Tuesday into Wednesday, an upper-level ridge will build
across the region, resulting in warm and dry conditions. This
ridge is a response to a deepening low-pressure system
approaching the Pacific Northwest Coast. Despite increased cloud
cover, temperatures are expected to rise above normal into the
lower 60s for the lower Valley, aided by increased southeasterly
winds. Southwesterly winds aloft will also elevate snow levels
to near 6000 feet MSL on Wednesday.

Precipitation ahead of the cold front associated with the
approaching low-pressure system will reach southeast Oregon by
Wednesday afternoon and push into southwest Idaho by early
Thursday morning. Precipitation water values approaching the
75th percentile by Thursday morning suggest decent rainfall
amounts. Ensembles indicate the Western Snake River plain has
about a 40% chance of exceeding 0.25” of rain Wednesday night.
Mixed precipitation is possible below 6000 feet in the mountains
Wednesday night, with accumulating wet snow possible on
Thursday.

LONG TERM...Thursday through Monday...A deep upper low will
move inland, putting us under moist southwest flow that will
support moderate mountain snow and valley rain Thursday and
Friday. Widespread precipitation will occur Thursday morning,
before tapering off to scattered coverage Thursday evening
through Friday. Snow levels won`t change much, as the coldest
airmass moves to our southwest, holding steady at 4000-5000 ft
MSL. Mountain valleys can expect 1-4 inches of snow, while
ridges will see 6-12 inches, increasing with elevation. As we`ll
be under a "warmer" portion of the cold airmass, snow ratios
are less than 10 to 1 in mountain valleys when the peak of the
precipitation comes. This leaves lots of room for the snow
accumulation forecast to change, hence the wide ranges. As the
upper low moves to our southwest, we`ll be left under a
deformation zone, which will continue to support scattered
precipitation through the weekend and allow temps to warm
slightly. By monday morning, precipitation chances mostly cease
as a large ridge begins to build over the upper low. The ridge
will support clearer skies and warm temperatures. Model
agreement on the pattern progression is fairly unanimous, with
only slight disagreements on the position of the deformation
zone. We could end up to far west of the zone, which would keep
us slightly drier than forecast over the weekend.

&&

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

&&

$$

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


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