922
FXUS65 KBOI 031549
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
949 AM MDT Fri May 3 2024

.DISCUSSION...Main ideas continue to be sunny and warmer wx today,
then increasing clouds and southeast/southwest winds and warmer
again on Saturday ahead of an approaching north Pacific cold
front. Moderate to heavy rain late Saturday/Saturday night as
the cold front moves through, then gusty west winds and much
colder wx Sunday with lighter showers of rain and snow. Also, a
20 percent chance of thunderstorms in eastern-most Idaho zones
Saturday afternoon and again Sunday afternoon. We`re considering
a Wind Advisory for the central Snake Basin and southeast Oregon
on Saturday, otherwise current forecast is on track. See "Prev
Discussion" (below) for details.

&&

.AVIATION...VFR. Local valley fog/stratus has mostly cleared, but
IFR conditions may still exist in isolated mountain valleys through
Fri/18Z. Mountains will see scattered to broken cumulus field with
bases 3500-5500ft AGL. Surface winds: variable or NW 5-15 kt, then S
to SE 10-20 kt this afternoon. Winds aloft at 10kft MSL: Variable
<10 kt, becoming S 10-20 kt Fri afternoon.

KBOI...VFR and clearing Friday. Light NW winds, becoming SE 10-15
kt Friday afternoon. Winds are set to increase significantly early
Sat morning to SE 20-25 kt with gusts to 30-40 kt.

Weekend Outlook...Widespread precipitation moves into SE Oregon mid-
morning Saturday, then into SW Idaho Saturday afternoon and will
continue across the region through Sunday. A 20% chance of
thunderstorms Saturday afternoon in s-central Idaho. Snow levels
6000-7000 ft MSL, lowering to 4000-5000 ft Sunday. IFR and
widespread mountain obscuration Saturday night and Sunday. Surface
winds: SE 15-25 kt with gusts 30-40 kt Saturday afternoon, W 5-15
kt with gusts to 20-30 kt Sunday.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Sunday night...Any lingering showers
wrapping around an exiting upper trough will dissipate by mid-
morning. The exiting trough is replaced by an upper ridge this
afternoon, resulting in dry weather and temperatures 5-10
degrees warmer than yesterday.

Upstream, a deep Pacific low will approach the NW coast on
Saturday. This system will be punctuated by heavy precipitation
and gusty winds as it pushes into the region late Sat/Sun. The
winds will increase out of the S-SE on Saturday in advance of
the low. Widespread sustained winds of 20-30 mph with gusts to
40 mph are expected. Locally stronger winds could set up over SE
Oregon Saturday and in portions of the Snake Plain east of
Boise that would require headlines.

A band of heavier precipitation will form ahead of a cold front
that will push into SE Oregon Saturday afternoon, then cross
into SW Idaho by evening. Marginal instability and surface
energy will support a 15% chance of thunderstorms over
s-central Idaho Saturday. Storms that do form will have a
favorable shear profile and could become strong. The front will
bring a wind shift to the NW Saturday night that will be
reinforced by flow aloft on Sunday. Precipitation will continue
on Sunday as it wraps around the low center which is forecast
to track through northern NV. The probability for precipitation
totals of over 0.25" has increased to greater than 80% across
SE Oregon and SW Idaho through Sunday. The axis of heavier
precipitation remains near the OR/ID border where the chance of
exceeding an inch of liquid through Sunday is 15-30%. Snow
levels ahead of the front will rise to 6-9kft Saturday evening,
falling quickly behind the front Sunday morning. This could
bring accumulating snow to SE Oregon as snow levels briefly
drop to around 3000 feet early Sunday. Otherwise much of the
accumulating snow is above 5500 after the frontal passage.
Precipitation continues in the mountains through Sunday night
while valleys trend drier.

LONG TERM...Monday through Friday...Northwest flow continues in
the wake of the exiting trough on Monday. Models show trailing
shortwave energy that will keep a chance of showers over the
region through Tuesday. An upper ridge will build along the
coast Wednesday, gradually folding inland through Friday.
Deterministic and ensemble solutions are in good agreement with
with this pattern change. Afternoon instability will support a
15-30% chance of showers over the mountains while lower
elevations remain dry. Temperatures through Wednesday are 10-15
degrees below normal, warming to near normal Thur/Fri.

&&

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

&&

$$

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DISCUSSION...LC
AVIATION.....JM
SHORT TERM...DG
LONG TERM....DG