412
FXUS65 KPIH 212118
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
218 PM MST Thu Nov 21 2024

.SHORT TERM...Today through Friday. An atmospheric river event
is continuing for the western Central mountains and the Sawtooth
mountains today. Pacific moisture has been moving into this area
due to an upper level low just off the Washington coast. A winter
storm warning is still in effect currently for moderate to heavy
snow through this evening for the western Central mountains and
the Sawtooth mountains. We will see very little snow on Friday
before the next system arrives on Saturday.

Models show this atmospheric river moisture to continue to stream
into the northern and western Central mountains and Sawtooth
mountains through today. Looking for snow amounts in the Wood
River valley up to around 1 inch or lower as snow levels have
risen to about 6500 feet and look to rise slightly higher. Look
for 4 to 6 inches of snow for Galena Summit and up to 16 inches,
possible higher, for extreme western slopes for Central mountains
and Sawtooth Mountains through this evening. Models consistently
show snow levels rising to around 6500 to 7000 feet by Friday.
Some models suggest snow levels could go as high as 7500 to 7800
feet in the northern Central mountains and Sawtooth mountains by
Friday. These rising snow levels will make it hard to know exactly
how much snow will happen in lower levels through the period,
especially for cities like Stanley, Ketchum, and Hailey. There is
a 20 to 30 percent chance for Hailey to get 1 inch of additional
snow through Friday morning. There is a 35 to 45 percent chance of
Ketchum to get 1 additional inch of snow. And there is a 70 to 80
percent chance for Stanley to get 1 inch of additional snow
through Friday morning. The NBM model shows a 45 to 55 percent
chance for Galena Summit getting 5 inches or more of additional
snow through Friday morning.

Outside of the Central mountains and the Sawtooth mountains, not
much rain and snow is expected for other areas until the weekend.
Only the Big Lost and Montana Divide will get light precipitation
mainly today, and to an lesser extent, Friday. Snow levels rise
to around 7000 feet for the Big Lost range and around 6000 feet
for the Montana Divide by Friday morning.

Expect very mild temperatures for today and tomorrow. Temperatures
in the valleys will reach the lower to mid 50s by Friday
afternoon.

More rain and snow is expected Saturday with cooler air moving
back into the area. Please see long term discussion for more
details.
Wyatt

.LONG TERM...Saturday through Thanksgiving Day. Next round of
precipitation arrives for Saturday, spreading east across most of
the forecast area. Timing of the best chances for precipitation
Saturday appear to be Friday night into early Saturday for the
Central Mtns, roughly mid-day for most of the Snake Plain, and
afternoon for the Eastern and Southeast Highlands. Daytime
temperatures above freezing will limit snowfall potential in lower
elevations, so most of the accumulation is expected to remain above
valley floors at this time. Given the predominant southwest flow,
the leading edges of the Central Mountains (Stanley-Hailey/Ketchum)
will continue to get the brunt of the precipitation, and a Winter
Storm Watch is now in effect for these regions. Higher elevations
surrounding Island Park also have the potential for occasionally
heavier snowfall during this period. Cold frontal boundary pushes
through on Saturday, with breezy afternoon winds.

Look for a relative break in the pattern Sunday as ensemble clusters
favor keeping main trough off shore. Next shortwave feature rotates
out of trough across Idaho Monday, bringing another round of snow to
the region. Moisture fetch not as well defined as current system, so
current probabilistic spreads favor less snow, though slightly
colder temps could induce better chances for snow at valley floors.
Ensembles slowly shift main trough inland and across East Idaho
through Thanksgiving Day. Additional snowfall through the holiday
travel period may be of concern to some.
DMH

&&

.AVIATION...Atmospheric river event ongoing for portions of East
Idaho, mainly impacting KSUN with periods of snow through tonight.
CIGS associated with this feature generally MVFR but expected to
drop to IFR during periods of heavier precipitation. The next best
chance of light precipitation shifts toward KBYI tonight, but
confidence is VERY low as the surface remains very dry and most of
the available moisture is expected to not reach the ground. There is
a low confidence threat of -SN for KIDA/KDIJ roughly 04z-10z
tonight otherwise most areas remain dry. A break in this pattern is
expected by mid-morning Fri morning, with dry VFR conditions all
terminals by Fri afternoon.
DMH

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 11 PM MST this evening for IDZ072>074.

Winter Storm Watch from Friday evening through Saturday evening
for IDZ072>074.

&&

$$