Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 212017
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
217 PM MDT Thu Sep 21 2017

.DISCUSSION...Deep upper trough in place over Western US. Main
circulation on water vapor sat imagery has dropped all the way
into Central California this morning. East Idaho remains ahead of
main trough in line with deepest moisture field. Band of continual
light precipitation remains parked over the region, though showers
now starting to appear across western Idaho and portions of the
central mountains. Wrap around moisture works back across the
Divide into the central mountains later today into Friday as main
precipitation band slowly pivots counter clockwise. Have not
changed QPF or Snow Amount values significantly from previous
forecast. Thus will continue Winter Weather Advisory through
Friday for zones 18/19/31/32 above 6500 feet, and continue to
message for generally 1-4 inches of snow lowering to 6500 feet by
Friday morning for the southeastern highlands. Moisture and cloud
cover appear to be sufficient tonight to keep overnight lows in
the Snake Plain a few degrees above freezing. Will hold off one
more day on any kind of temperature-related headlines.

Center of upper low digs south through the Great Basin Friday
night into Saturday, pushing the deeper moisture and dynamics
east of the region. Friday night and Saturday should see a
significant decrease in precipitation for most areas. As upper low
slowly works east through the southern Great Basin, expect wrap
around showers to shift back into the region late Saturday,
Saturday night and Sunday, mainly impacting areas along the WY and
UT borders. Temperatures remain cool to cold through this time
period, with overnight lows hovering around freezing for the Snake
Plain. Trough axis still projected to slip east of the region
Sunday night into Monday, allowing temperatures to start to warm
slightly with ridge building into the Western US. A few lingering
showers may be possible along the WY border as the low shifts
away, but most of the area should remain dry. Shortwave feature
drops out of BC Canada Tuesday, and could lead to showers across
the region that afternoon, mainly in areas closest to the Divide.
DMH

&&

.AVIATION...A strong upper-level low pressure system will continue
to impact flight conditions across the region this afternoon into
Friday. Expect continued rain showers this afternoon into tomorrow
for KPIH, KIDA, and KDIJ and more of a drizzle for KSUN and KBYI,
with cooler air moving in. Could see some snow mix in with the
drizzle/rain at KSUN and KDIJ this evening. Will see continued
fluctuating conditions at all sites based on precipitation timing
and intensity. However, overall MVFR conditions look to be most
common through the period. Will likely see conditions improve at
times to low end VFR during breaks in the precipitation, and
possibly drop to IFR during times of heavier precipitation. Wyatt


&&

.FIRE WEATHER...Cool and wet conditions will continue today and
Friday as the area remains under a strong upper-level low pressure
system.  Expect light valley rain and mountain snow showers in the
Central/Pahsimeroi mountains with more widespread moderate valley
rain and mountain showers elsewhere. Expect a drying trend this
weekend as the low weakens and begins to shift east, leaving
lingering rain/snow shower activity over the Central Mountains and
Eastern Highlands. By Sunday these showers will be mainly over the
Eastern Highlands. Temperatures will gradually warm up this weekend
into mid next becoming near normal as high pressure strengthens.
Wyatt


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM MDT Friday for IDZ018-019-031-
032.

&&

$$


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