044
FXUS65 KBOI 230410
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
910 PM MST Sat Feb 22 2025

.DISCUSSION...The moist Pacific plume (a.k.a. atmospheric
river) is still on track to arrive later tonight and persist
through Sunday for widespread precipitation. The heaviest totals
are progged in central Idaho and the mountains of SE Oregon.
Snow levels will remain well above valley floors, except
starting out as snow or a rain/snow mix in the north (e.g.
McCall) before changing to rain in the afternoon as snow levels
continue to rise. No changes were made to the forecast this
evening.

&&

.AVIATION...VFR, becoming widespread MVFR/IFR/LIFR with rain and
snow late tonight through Sunday as a storm system moves into
the region. Snow levels rising through Sunday with rain expected
in all terminals, except KMYL which will start off as snow or a
rain/snow mix, changing to all rain in the afternoon. Mountains
obscured. Areas of LLWS, mainly in SE Oregon. Surface winds:
SE-SW 5-15 kt with gusts to 25 kt. Winds aloft at 10kft MSL:
W 15-30 kt increasing to 30-50 kt early Sunday morning.

KBOI...VFR with rain developing by Sun/12Z. There is a chance
30-50% chance of MVFR conditions on Sunday. Surface winds:
SE 8-15 kt.

&&

.HYDROLOGY...Moderate to heavy rain along with low elevation
snowmelt will cause significant rises on rivers, creeks, and
streams in SE Oregon, and portions of SW Idaho (particularly in
the Weiser Basin) beginning Sunday and Monday. Soils are likely
frozen in some of the lower elevations as well which will
enhance runoff. Snow and ice may lead to clogged culverts and
ditches causing ponding of water in poor drainage areas.
Additionally, ice jams could develop on any rivers or streams
with existing ice cover. Rivers in SE Oregon (including the
Malheur River) and the Weiser River will continue to run high
through next week, potentially reaching bankfull or near minor
flood stage. Those with interests along rivers, creeks and
streams should continue to monitor the forecast as there is
uncertainty in how much response the lower elevation rivers,
creeks and streams will see.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Monday night...Rain and snow will
develop tonight as westerly flow pushes a ribbon of deep
moisture into region. This forecast package continued the recent
upward trend in the precipitation amounts expected with the
storm. Overall, widespread 1"+ liquid totals are looking certain
(greater than 80-90%) through Monday across the Upper Weiser
Basin and the mountains of e-central Oregon and w-central Idaho
while greater than a 50% chance of 2"+ amounts exists across
higher peaks of the interior w-central ID and Boise mtns (east
of a line from the Long Valley to Idaho City). The flow aloft
will produce a precipitation shadow across the Snake Plain,
following I-84 from Baker City through Glenns Ferry (areas to
the north and east seeing higher totals). Snow levels will start
out between 3500-4500 feet in Baker County and the w-central ID
and Boise mtns tonight, rising above 5500 feet by midday
Sunday, before peaking between 6500-7500 feet Sunday night.
While mtn valleys could see up to 2 inches, the heaviest snow
totals through Monday will be above 6500kft where 10-16" of wet
snow is expected. Areas to the south, to include the Boise
foothills along the Snake, will see snow levels quickly rise to
around 7kft Sunday morning, and continue upward reaching
7500-8500 feet Sunday night. This will limit snow accumulation
to just the highest peaks. Have kept a slight chance of freezing
rain in sheltered valleys through early Sunday, mostly across
northern Malheur County, southern Baker County and Jerome
County. Expect any freezing rain to be light and shortlived with
minimal impact to road surfaces. There remains a hydrologic
concern with this event especially across lower basins that hold
a snowpack. The current Hydrologic Statement and Hydro section
below cover this threat in more detail.

The heavier precipitation will taper off across SE Oregon and
lower elevations of SW Idaho Sunday night while flow aloft keeps
the rain/snow going in the mountains. Brief upper level ridging
on Monday will slow down the mountain precipitation in the
afternoon and keep valleys dry. This will allow for temperatures
to warm into the mid 50s across the Snake Plain to low 40s in
mtn valleys. Moist southwest flow will start up another round
of mostly mountain rain/snow Monday night as a storm system
moves onto the WA coast. Snow levels will start between
6500-7500 feet Monday evening, falling to between 4000-6000 feet
early Tuesday morning.

LONG TERM...Tuesday through Saturday...Good agreement that the
region will be dominated by upper-level ridging Tuesday Night
through Saturday. Nearly 100% of ensemble guidance along with
deterministic runs support this pattern, making for increased
confidence. Upper level heights are forecast to approach 565 to
570dm making a strong case for above normal temperatures. NBM
guidance is indicating temperatures 5 to 10 degrees above normal
area-wide. By the end of the week there is a 15-20% chance of
temperatures above 60 degrees across eastern Oregon, and a
40-60% chance in the lower valleys of southwest Idaho. The next
precipitation maker is slated for late Saturday.

&&

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

&&

$$

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DISCUSSION...BW
AVIATION.....BW
HYDROLOGY...TL/BW
SHORT TERM...DG
LONG TERM....MC