Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 180855

Area Forecast Discussion
National Weather Service Pocatello ID
255 AM MDT WED MAY 18 2016

.SHORT TERM...Today through Friday night. Mild temperatures will
continue today as broad southwest flow will be in place in advance
of a stout Pacific trough/closed low. This system will be
responsible for a prolonged period of unsettled conditions across
the region for the next several days. One weak wave in advance of
this system will focus shower and thunderstorm activity over the
Central Mountains and MT border region this afternoon. Locally
heavy rainfall will be possible with this activity. Skipping ahead
to Thursday...this will be the period of potentially greatest
impact for the short-term. A sharp cold front is forecast to
swing across the region. The cold front in conjunction with
favorable dynamics will advance across the region during the
afternoon and evening...when instability will be at its peak. Wind
shear will be supportive of organized thunderstorms as well. In
addition...a ribbon of enhanced atmospheric moisture will
accompany the frontal passage. The combination of moisture...lift
and instability with the addition of favorable wind shear will
set the stage for a few strong or potentially even isolated severe
thunderstorms across the Snake Plain and Eastern Highlands
Thursday afternoon and evening. Storms will have the potential to
produce strong winds...hail...heavy rainfall and frequent
lightning. Behind the cold front...lingering moisture and dynamics
will aid in continued shower development...with numerous showers
persisting across SE Idaho through the day Friday. By Friday
night...snow levels fall to near 7000 feet elevation across the
Central Mountains...bringing accumulating snow to mid and upper
slopes. AD/Huston

.LONG TERM...Saturday through next Wednesday. Both the GFS and
ECMWF show the closed upper low over Oregon filling and ejecting NE
through the region Saturday/Saturday night while secondary energy
digging into the WRN extent of the trough helps to maintain a broad
upper trough over the region Sunday and Monday. By Tuesday, another
PAC low digs SE into WRN Canada eventually interacting more or less
(depending on which model you favor) with the broad upper trough
positioned over the NW states. All in All, the period looks to favor
fairly active convection each afternoon/evening with ejecting short-
wave energy expected to enhance the precipitation potential from
time to time. Statistical guidance suggests fairly cool daytime
highs throughout the period and have seen no reason to stray too far
from that guidance given the persistent troughiness over the region.


.AVIATION...Early morning satellite imagery was showing a transient
upper ridge advancing into Idaho ahead of a deep low pressure system
which was moving into the WRN Canadian coast. Some mid-level CIGS
were also visible on satellite imagery and are expected to
transition through the region this morning. By this afternoon,
residual moisture coupled with daytime heating should be enough to
support scattered convection favoring the mountains. To that end, it
looks as if KSUN may see convective buildups in the VCTY of the
terminal (mainly over the mountains to the north and east) and
drifting ESE with time. With the steering flow driving the cells
ESE, KBYI and KPIH most likely will not see any impacts from
convection over the SRN and SE mountains, KIDA on the other hand may
see a slight risk of a cell working out of the CNTRL mountains and
across the upper Snake River Plain late this afternoon/evening and
thus will add mention of a VCTS to that terminal. Huston


.PIH Watches/Warnings/Advisories...

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