Area Forecast Discussion
Issued by NWS Pocatello, ID

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624
FXUS65 KPIH 230953
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
253 AM MST Fri Feb 23 2018

.SHORT TERM...Today and Tonight...Snow showers are falling in
three distinct bands this morning from Monida Pass and across the
Continental Divide region, from near Rexburg through Ririe to
Shelley, and yet another band from the Palisades across Lava Hot
Springs, Preston, Malad Summit to Holbrook Summit. Anticipate
these early morning showers to bring light snow accumulations of
less than an inch, but this will continue to leave already
icy/slushy roadways in that state. The Bear Lake region is
expected to pick up more accumulated snowfall through the
afternoon hours. Expect an additional inch or so of snowfall on
mountain passes this afternoon, especially Emigration and
Georgetown Summits. Snow will taper off along the Divide by the
early afternoon. Meanwhile, increasing west and southwest winds
across the Snake River Plain remains in the forecast for the
afternoon and early evening with sustained speeds of 15 to 20 mph
forecast and no additional snow showers expected for the day.

Saturday and Sunday...The next weather system barrels in early
Saturday with impacts starting in the Central Mountains and in the
Island Park/Continental Divide region. As the day advances, a
rather potent burst of energy tracks through SE Idaho and brings
widespread snow. At this time, impacts are expected to be most
significant during the middle of the day across the Snake River
Plain and for areas south and east of the Interstate Corridor.
Snow will begin to taper off in the Central Mountains by the
overnight hours. Widespread snow amounts of 1 to 3 inches at
valley floors are anticipated for Saturday alone with over a foot
forecast over 8000 ft. Confidence is building in this particular
event and will rate it at moderate to high though snowfall amounts
are on the lower spectrum of confidence. There will be a break in
between weather systems early Sunday morning for most places;
though there will be some exceptions (locations along the Wyoming
border). Winter does not loosen its grip though and more snow
fills right in during the day Sunday more or less in the same
places it will on Saturday. A few locations may miss out on
Sundays storm, namely the Magic Valley and places further south.
NP/Huston

.LONG TERM...Monday through next Friday. The GFS, ECMWF, and GFS
ensembles appear to be in good agreement through about Wednesday and
then both the operational GFS and ECMWF fall to the extremes of the
general GFS ensemble idea of keeping some sort of broad trough over
the west Thursday and Friday likely owing to the struggles that the
models have been having modeling the short-waves breaking over the
ERN Pacific ridge into North America. Have generally tried to
accentuate the details in the first half of the period where the
models are in better agreement which would be a higher precipitation
potential Monday with the passing trough then drier Tuesday behind
the exiting system and before the next incoming system Wednesday.
Beyond Wednesday, the general idea was to try and blend where
possible while maintaining some mention of precipitation given the
ensemble support for a broad trough over the region. Have strayed
little from the below normal statistical guidance. Huston

&&

.AVIATION...Early morning satellite imagery was showing an upper
trough gradually shifting into SRN Idaho with the brunt of the lower
CIGS and snow shifting east into the Wyoming border region with the
leading edge of the trough. Numerical models generally favor the
idea of improving conditions today followed by an influx of moisture
and lower CIGS (predominantly MVFR) into the region late tonight as
the next upstream disturbance hits the Washington coast. Huston

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$



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