272
FXUS65 KBOI 010327
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
927 PM MDT Tue Apr 30 2024

.DISCUSSION...An upper level shortwave is moving over
southcentral WA into NE Oregon toward the Blue Mountains
tonight. The system will track southeastward overnight and into
the central ID mountains by Monday morning. This system will
bring snow showers as it passes through. Current forecast and
ensembles not resolving mesoscale features of this system, so
have adjusted the forecast to add a mention of rain and snow
showers (15 percent chance) overnight into midday Wednesday.
Some of these showers have the potential to produce snow
accumulations 1 to 2 inches as they pass through. Forecast has
been updated to add mention of showers in the Treasure Valley.
Cold air aloft, with
-33C at 500mb on Wednesday morning through afternoon will fuel
showers during the afternoon. Have added mention of showers on
Wednesday afternoon across much of the area, with the exception
of southcentral OR, where warmer air aloft will keep conditions
stable.

&&

.AVIATION...Mainly VFR. Isolated to scattered rain/snow showers
north of KBNO-KBOI-KSUN line. Snow showers obscuring mountains and
producing brief MVFR conditions. Snow levels around 3000-4000 ft
MSL, lowering about 500 ft overnight. Surface winds: W-NW 5-15 kt,
with gusts to 20-25 kt through Wed/05z near KTWF/KJER. Winds aloft
at 10kft MSL: W to NW 15-25 kt.

KBOI...VFR with scattered/broken clouds 6000-9000 ft AGL. Isolated
showers will pass north of terminal overnight, with a 15%
chance of showers entering the 10 mile vicinity. Snow levels as
low as 3000- 3500 ft MSL this evening, lowering to 2700-3300 ft
MSL by Wed morning. Generally NW 5-15 kt with gusts to around 20
kt through 04Z.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Thursday night...Showers have
begun ahead of the approaching shortwave, primarily in Baker
County and the West Central Mountains of Idaho. Snow has been
spotted as low as 2600 feet near Cambridge, Idaho, but
significant accumulation is only expected above 4500 feet.

High-resolution models predict showers to stay north of a line
stretching from Burns to Ontario to Stanley throughout this
afternoon and evening. There`s a possibility of weaker showers
in the Lower Treasure Valley near Caldwell and Nampa, but any
precipitation is unlikely to reach the ground. The upper-level
jet over our southern forecast area will bring breezy winds
overnight, along with the chance for stronger showers producing
lightning strikes and graupel. While there`s a potential for
mixed precipitation down to 2500 feet, surface temperatures
should stay above freezing, limiting significant accumulation to
elevations above 4500 feet.

Early Wednesday, a weak cold front will pass through,
maintaining increased winds in the area, especially affecting
the Western Snake River Plain into the afternoon. This could
help keep min temperatures just above freezing especially in
the Lower Treasure and western parts of The Upper Treasure
Valley tonight. Gusty winds may reach advisory levels in the
Western Magic Valley and Camas Prairie, although the likelihood
is currently estimated at about 30%, lower than earlier
forecasts.

Thursday will offer a brief respite from these
systems, with dry conditions but below-normal temperatures
persisting. Northwesterly flow will keep winds elevated in the
valley.

LONG TERM...Friday through Tuesday...A weak ridge will bring
brief dry conditions Friday. Upper level winds will quickly turn
southwesterly as the next low pressure system approaches the
PacNW Friday/Saturday. Temperatures will rise to near normal
both Friday and Saturday from the brief high pressure and
southerly influence. However, models become out of alignment on
the path of this incoming low this weekend and create
uncertainty in the forecast. Approximately 50% of latest
ensemble members carry the low farther south into California,
keeping temperatures over E Oregon and SW Idaho slightly warmer
while slowing down the arrive of showers/thunderstorms over the
area. Meanwhile, the rest of the ensemble solutions track the
low right overhead, supporting notably cooler temperatures and
an earlier arrival of showers/thunderstorms. As a result, the
current forecast for the weekend has an influence of cooler
temperatures overall, along with 40-60% chance of precipitation
with high uncertainty in snow levels. Thereafter, models keep a
cool and showery northwest flow over the forecast area early
next week with slightly below normal temperatures anticipated.

&&

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

&&

$$

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