Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 291958

Area Forecast Discussion
National Weather Service Pocatello ID
158 PM MDT THU SEP 29 2016

.SHORT TERM...Tonight through Sunday. Early afternoon satellite
imagery showed a low pressure system setting up off the NW coast
with an unstable SW flow across the Great Basin. Regional radar
imagery showed scattered convection lifting NE into/across SE Idaho.
Numerical models continue to show diurnally and elevationaly favored
convection this afternoon and Friday afternoon as the low drifts
slowly south into the Oregon coastal waters. By Friday night, a
second PAC low digs sharply south along the Canadian coast absorbing
most but ejecting some of the Oregon coastal low inland across
Oregon Saturday morning and Washington Saturday afternoon.  An
associated surface frontal boundary will make its way east through
SRN Idaho Saturday morning resulting in an area of enhanced
precipitation potential across the CNTRL mountains in the morning
transitioning into the ERN highlands by afternoon with breezy
conditions developing within the Snake River Plain. The
aforementioned Canadian low digs south into the Oregon coastal waters
Saturday night resulting in a continuation of the unstable SW flow
across the region and scattered afternoon showers. The going
forecast contained most of this thinking and my work today was to
accentuate those areas and times where precipitation was favored.
Temperatures remain unseasonably warm Friday before cooling to near
seasonal norms Saturday and Sunday. Huston

.LONG TERM...Sunday night through next Thursday. Model solutions for
remain in general agreement with mean upper trough situated over the
coastal states Sunday night. This translates into greater chances of
precipitation leading into next week. ECMWF is adjusting the track
of the upper low circulation a bit further north while the GFS
maintains a track more southward into central Utah. The strongest
forcing will be along the track of the upper low, with the greatest
influence on southeast Idaho Monday and Monday night. GFS MOS
guidance is suggesting cooler temperatures next week, but it is
beginning to trend a bit higher. Bumped up max/mins slightly, which
also puts us in better congruence with our neighbors.  The upper low
shifts eastward Tuesday morning so we will see PoPs associated with
the wrap-around along the Eastern Highlands while precip chances
quickly diminish elsewhere. Models generally keep extended periods
dry as weak ridging builds over the East Pacific.  Hinsberger

.AVIATION...Showers are ongoing at DIJ this morning, and should
continue through much of the afternoon. Isolated thunderstorms will
be possible as airmass destabilizes this afternoon and evening. NAM
is drier than the GFS in the overnight hours so keeping VCSH in most
locations. Overall, expect VFR conditions to prevail, but DIJ may
see lowered cig/vis with heavier showers. This is supported by WRF
forecast soundings. Hinsberger

.FIRE WEATHER...Moist and unstable air is surging northward into SE
Idaho this morning ahead of the low pressure disturbance moving into
the coast. Scattered showers with isolated thunderstorms are
expected from about noon until sunset today with most activity
angled across the South Central and Eastern Highlands. There will be
some showers in the Central Mountains. Estimate precipitation from
0.03 to 0.11 inches with higher amounts from isolated stronger storm
cells. Activity diminishes this evening, then focus on Friday will
be a band of showers and isolated thunderstorms oriented along a
surface front with best precipitation from near Ketchum to
Leadore,around 0.10 to 0.15 inch. A pretty good band of showers
should form over the Snake Plain on Saturday. A temporary period of
dry air is anticipated Saturday night and at least part of Sunday.
Then the disturbance off the Pacific tracks across northern Nevada
and Utah with some showers wrapping back into Idaho. May not be a
lot of the storm system left by then, but snow levels drop to near
7000 feet elevation in the central mountains, sloping to about 8000
feet towards Bear Lake. RS

.PIH Watches/Warnings/Advisories...None.

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