657
FXUS65 KBOI 311009
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
309 AM MST Fri Jan 31 2025

.SHORT TERM...Today through Sunday night...The moist conveyor
belt off the Pacific (known as the atmospheric river) made it
onshore as precipitation was spreading into the Pacific
Northwest. The eastern edge of the precip shield will reach SE
Oregon and far SW Idaho this morning, then into the remainder of
SW Idaho this afternoon. A strong mid-level flow will enhance
the precip rates across the higher elevations, especially in
central Idaho. Initially, snow levels will start off near valley
floors, then rise to 4-5000 feet this afternoon. The exception
will be north of Ontario where snow levels are expected to
remain below 4000 feet as the snow continues down to valley
floors. Southeast winds have already developed across the Snake
Plain east of Boise with gusts to around 30 mph from Mountain
Home to Jerome. The southeast winds will limit snowfall amounts
in the Upper Treasure Valley due to downslope drying effects.
However, the Lower Treasure Valley around Ontario has a better
chance of seeing accumulation snow of around an inch with
locally up to 2 inches. Several inches of snowfall are expected
across the higher elevations in the north, mainly central Idaho.
There may also be pockets of light freezing rain in the wind-
sheltered lower valleys, but the probability is less than 20
percent. A Winter Weather Advisory is in effect for Baker
County, the Lower Treasure Valley in Oregon, and the Upper
Weiser Basin today as the snow is expected to diminish this
evening. Some of those stronger mid-level winds will mix down to
the surface across southern areas near the Nevada border today
with gusts of 40 to 50 mph, mainly along the ridges.

The precip will diminish further on Saturday as the moist plume
shifts further south. However, strong mid-level flow will
continue to enhance the snowfall in central Idaho. A Winter
Weather Advisory is in effect for central Idaho later this
morning through Saturday. The moist plume shifts northward on
Sunday with precipitation spreading from south to north. Snow
levels will be near valley floors, except rising to around 5000
feet near the Nevada border. Light snowfall accumulations are
possible in the valleys along with several more inches in the
mountains.

.LONG TERM...Monday through Friday...A cool and active pattern
will persist through the long term period, bringing intermittent
precipitation and generally below normal temperatures.

Cool and moist zonal flow will bring periods of valley rain and
mountain snow to the region on Monday and Tuesday, as an
atmospheric river continues to pummel California through the
midweek. Model agreement remains high through Tuesday, with
excellent forecast confidence in above normal precipitation
amounts. There is a sharp gradient between the incoming low
pressure center over Vancouver Island and southwest flow across
the southwest, which will result in a large spread of snow
levels across our region through Wednesday. Baker County and the
West Central Mountains will generally see snow levels at valley
floors (<3000 ft) while regions near the Nevada border will see
snow levels closer to 4500-5000 feet. This will impact snow
totals across the region, with much heavier accumulations in the
mountains (anywhere from 8-12 inches near McCall and 20-30
inches over Banner Summit by Wednesday morning) and valley
rainfall totals around 0.25-0.50 inches by Wednesday morning.

Model agreement decreases by Wednesday with the evolution of
the long wave trough and cold Canadian air mass. The trough will
become negatively tilted and dig deeply over the northwest,
bringing cold temperatures and high elevation snow showers on
Thursday and Friday. The forecast uncertainty comes from the
extent of the tilt of the trough along with the persistence of
the fetch of moisture from the Pacific Ocean. Forecast
uncertainty therefore remains high for Thursday and Friday.
Despite the uncertainty, there is some reasonable confidence in
mountain snow showers and below normal temperatures for the
region through the end of the work week.

&&

.AVIATION...Rain/snow arriving from the west this morning,
creating areas of MVFR/local IFR. Pockets of freezing rain near
KGNG-KJER and KONO. Snow levels at/near valley floors, rising to
3k-5k feet MSL Fri afternoon. Mountains becoming obscured.
Surface winds: E-S 5-15 kt. Becoming SW-SE 10-20 kt by Fri/17Z,
with gusts to 25-35 kt. Gusts up to 40-50 kt near NV border and
over high terrain. Areas of low level wind shear tonight. Winds
aloft at 10kft MSL: SW-W 20-30 kt, increasing to 35-50 kt this
afternoon.

KBOI...VFR tonight. Mix of rain/snow arrives from west between
Fri/16Z-18Z. Transition to all rain between Fri/19Z-21Z. Precip
will create low VFR/MVFR ceilings. Winds: SE 5-15 kt, gusts to
20-25 kt by late Fri morning.

Weekend Outlook...Periods of precipitation with MVFR and local
IFR conditions through the weekend. Snow levels: near valley
floors for northeast OR and w-central ID, higher around 4k-5k
feet MSL closer to NV border. Mountains obscured. Surface winds:
SE-SW 5-15 kt with gusts to 25 kt through Saturday morning,
shifting to the W-NW 5-15 kt with gusts 20-25 kt Sat afternoon
through Sun.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Air Stagnation Advisory until 5 AM MST early this morning
     IDZ011>016-029-030-033.
     Winter Weather Advisory from 8 AM this morning to 5 PM MST
     Saturday IDZ011-013-028.
     Winter Weather Advisory from 8 AM this morning to 5 PM MST
     this afternoon IDZ033.
OR...Air Stagnation Advisory until 5 AM MST /4 AM PST/ early this
     morning ORZ061>064.
     Winter Weather Advisory from 8 AM MST /7 AM PST/ this morning
     to 5 PM MST /4 PM PST/ this afternoon ORZ062-064.

&&

$$

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SHORT TERM...BW
LONG TERM....SA
AVIATION.....SA