Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 170954
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
254 AM MST Sun Feb 17 2019

.SHORT TERM...Today through Tue night. Weak low pressure residing
over the northern intermountain west will allow a moist air mass
to cross through and bring light precipitation to both mountains
and the Snake River plain in the forecast area. Hard to say which
locations outside of the eastern Magic Valley and south central
highlands where it will also snow, but the focus is definitely
south central Idaho. However, snowfall amounts in the Snake River
plain barely reach one inch in the eastern Magic Valley between
now and midnight, with plain areas north of Fort Hall only getting
a skiff to half an inch. The mountains and highlands are only a
little heavier in snow accumulation, with the heaviest at 4 to 8
inches over the Galena Summit during the same timeframe. most
locations will see 0.5 to 2.5 inches. By Mon midday, the upper
level trough has moved to the east, opening the door for air from
interior Canada to move into the eastern Gem State. By Mon night,
the clearer skies will mean some areas of bitter cold, mostly in
the northern third of the forecast area. The outbreak of cold air
is short-lived, as by Tue evening the next coastal storm will be
far enough east to shift the air flow to west and southwest. Some
doubt on just how much precipitation will come with the low in the
first 12 hours, with the GFS heavier than the NAM. No strong
surface features to bring any kind of significant wind; besides
the light snow today and this evening, the only item worth
mentioning are the large temperature swings in the overnight low
from the mild temperatures tonight and Tue night and the
aforementioned chilly lows for Mon night. Messick

.LONG TERM...Wednesday through Sunday. Unsettled pattern redevelops
early in the extended period. Models are consistent with shortwave
digging through the PacNW and reinforcing deep trough over the
western states. Snowfall redevelops across East Idaho through the
day and continues into Wednesday night as upper low drops through
Nevada. Precipitation weakens into Thursday with most of the
moisture consolidated into the base of the trough. Weak dynamics
continue with trough axis extended north across the region allowing
showers to continue into Friday higher elevations. Headed into the
weekend, the ECMWF deepens another low off the coast, allowing a
slight ridge to build across Idaho. This solution, however, is an
outlier with the operational GFS, Canadian, and GEFS all supporting
a more eastward solution with an open trough digging into the region
from BC Canada. This consensus solution allows weak precipitation to
continue into the weekend. Overall temperatures remain fairly
consistent through the extended period, and stayed with a consensus
blend. DMH

&&

.AVIATION...Snow showers will be the rule today, and the convective
nature of the precipitation will mean widely varying conditions.
Outside of the snow showers, look for MVFR to VFR ceilings and
visibility. Within the snow showers, conditions drop to IFR. No
terminal will be exempt through the day today. Moving past the
evening into the overnight hours, precipitation chances drop
somewhat, particulary for the Snake Plain terminals KBYI, KPIH and
KIDA. KSUN may hold on to the threat for snow showers the longest
through the overnight. DMH

&&

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

$$



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