Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 200851

Area Forecast Discussion
National Weather Service Pocatello ID
251 AM MDT FRI MAY 20 2016

.SHORT TERM...Today through Sunday night. A strong upper level
low pressure system currently located just off of the Oregon coast
will meander south and east across the Northern Great Basin
before eventually shifting east and north across Central Idaho
Saturday night into Sunday. Much of the western portions of the
forecast area will reside beneath the exit region of a
cyclonically curved jet rounding the southern periphery of the low
center today and into Saturday. As a result, showers currently
located over the SE portion of Idaho will shift into a linear N/S
oriented band over the southern Snake Plain, Eastern Magic Valley
and Central Mountains by late this morning, with this band slowly
creeping westward through the day today before becoming nearly
stationary this evening and overnight. Locally heavy precipitation
is possible beneath this precipitation axis today and tonight.

As the upper low approaches, the dynamics driving precipitation
generation become less organized late Friday night through the
weekend, forcing a transition from organized precipitation bands
to a precipitation regime that is more showery in nature. Even so,
the presence of sufficient atmospheric moisture combined with
daytime instability will mean locally heavy showers and isolated
thunderstorms...particularly during the afternoon and early
evening hours Saturday and Sunday, with the heaviest and most
widespread precipitation falling across the Central Mountains both
days. Speaking of the Central Mountains, snow levels are expected
to drop to around 7000 feet tonight, and perhaps nearing 6000 feet
Sunday. As a result, several inches of wet snow are possible for
mid-and upper slopes, including Galena Summit where some slushy
roads may develop, particularly at night. Gusty winds will be
common today across far SE Idaho creating some potentially
difficult travel across East-West roads. Location of strongest
winds will shift across the Snake Plain both Saturday and Sunday,
particularly on Sunday, perhaps necessitating a Lake Wind Advisory
for American Falls Reservoir. AD/Hedges

.LONG TERM...Monday through Friday night. Both GFS and ECMWF in
agreement with the upper trof dominating the Pac NW thru Thursday...
and to a lesser extent on Fri. This is a departure from earlier runs
which showed a prominent upper ridge over the west on Thu. This will
result in scattered showers and aftn tstms thru Thu...with somewhat
decreasing coverage on Fri. By Wed precip chances are highest
over the mtns...decreasing in the valleys. Temps do warm up a
little during the week. Hedges


.AVIATION...The deep upper low over the Pac NW will send another
round of showers/tstms across the region this morn. Ocnl MVFR cigs
possible. Models showing a dry slot developing over eastern ID by
aftn...which should bring some relief to KPIH and KIDA. KBYI and
KSUN will likely see showery conditions continue thru the aftn as
the main band of precip shifts westward to central and south central
ID. Breezy conditions also expected this aftn. Hedges


.PIH Watches/Warnings/Advisories...

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