Area Forecast Discussion
Issued by NWS Pocatello, ID

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439
FXUS65 KPIH 182007
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
207 PM MDT Mon Sep 18 2017

.SHORT TERM...Tonight through Tuesday night. Upper low continues
to shift into PacNW with center located off Vancouver BC coast.
Shortwave sliding through OR/WA this afternoon already producing
precipitation across the central mountains this afternoon. Some
weakly enhanced activity but little to no lightning thus far.
Could see a few lightning strikes still as stronger convective
activity approaches from OR but little confidence in anything past
00Z. Winds strongest across the Upper Snake region including the
Arco Desert, but remaining below headline levels. Thin clearing
band shifting toward the region so could still yet see a nudge
upward in winds, so will cautiously leave the Lake Wind Advisory
in place. Otherwise, expect moisture band currently over central
mountains to sag SE across the rest of the region overnight. Have
pushed PoP higher across the area especially for higher elevations
tonight, as that should coincide with heaviest precipitation.
Snow levels do drop, but not significantly, and accumulations
should remain above 6500 ft in the central mtns and 7500 ft in the
eastern highlands. Higher elevations remain very unsettled into
Tuesday with fast zonal flow aloft. Surface gradient also remains
strong so expect windy conditions to continue. Break in the
precipitation begins late Tuesday and continues into Tuesday night
with flat ridge ahead of next shortwave associated with PacNW
trough. DMH

.LONG TERM...Wednesday through Monday. Upper trough amplifies into
western states early Wednesday, with next shortwave pushing
precipitation into the central mtns by the afternoon. Cold front
slides across the region during the day, reinforcing cooler air
mass already in place, and dropping snow levels down to 5500 ft by
Thursday morning. Heaviest precipitation remains associated with
the front, so little snow fall expected to reach valley floors.
Made no changes to going forecast beyond this point. Upper low
significantly deepens over the northern Rockies. Will likely see
showers continue mainly over higher elevations until low opens and
trough axis shifts east late Saturday. Guidance continues to show
cold overnight lows Thurs through the remainder of the period.
Frost warnings are a very strong possibility, and portions of the
Snake Plain may need a Hard Freeze warning if the trend continues.
DMH


&&

.AVIATION...Rain associated with approaching upper low has begun
across the Central Mountains, and should reach KSUN early this
afternoon. Other locations should see showers begin early this
evening. BUFKIT forecast soundings show potential for lowered
ceilings during the rainfall. Expecting MVFR or IFR ceilings
tonight. Another concern will be winds. An approaching cold front
will keep winds elevated, and we will see gusts up to 30 kts this
afternoon and evening. Hinsberger


&&

.FIRE WEATHER...Cool, wet, and windy conditions will continue most
of the coming week as we remain under the influence of a deep upper
low and attendant trough. Winds 30 to 35 mph will be possible
tomorrow afternoon across the Snake Plain, though humidity will of
course limit the threat of extreme fire behavior. A second push of
cooler air will occur Wednesday afternoon as a cold front blasts
through the area. Cool weather with high humidity will continue
through the rest of the week as we remain under the influence of a
high-amplitude upper trough. Hinsberger


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Lake Wind Advisory until 8 PM MDT this evening for IDZ021.

&&

$$



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