Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 210905

Area Forecast Discussion
National Weather Service Pocatello ID
305 AM MDT WED SEP 21 2016

.DISCUSSION...Moisture from a few different sources will work its
way into our region today, tomorrow and Friday. Moisture from a
shortwave trough is currently the dominant feature over our area,
and is providing isolated showers over Nevada. Additional moisture
includes tropical moisture and remnants from what was once
Hurricane Paine in the Eastern Pacific Ocean. Our widespread
rain/snow event will begin today with isolated and scattered rain
showers over the central mountains with increasing coverage by the
afternoon. Rainfall amounts will top out around 1/4 inch in these
areas for today, with 1 to 2 inches of snowfall at highest
elevations (of which is expected to increase to 2 to 4 inches
through Friday). For the Snake Plain areas and elsewhere, coverage
will increase greatly later this afternoon with lighter rainfall
amounts expected. Instability will be marginal this afternoon but
the greatest likelihood for thunderstorms looks to be over the
Eastern and Caribou Highland locations with a similar pattern
setting up for Thursday afternoon. As we go into the overnight
hours, rainfall will shift focus a bit to the east and south where
a decent chance, about 50%, to obtain 1/4 inch of rainfall exists
across the Southern Highlands.

Thursday morning shows another 50% chance for 1/4 inch of rainfall
in portions of the Southern Highlands, especially across the
southern Caribou-Targhee NF. For the rest of Thursday, look for
continued rain showers with a chance for thunderstorms with
increased coverage expected overnight into Friday morning.
Overall, for our area, highest rainfall accumulations look to be
setting up along the Idaho/Utah border including the cities of
Preston, Mink Creek, Malad City, Soda Springs. Rainfall amounts
will continue to be amended as rain begins to fall and the event
unfolds. Right now forecasts are calling for 2 to 4 inches across
this area over a 3-day period starting this afternoon. Snow may
fall at highest elevations in these areas as well Thursday with 1
to 3 inches possible through Friday. Other areas in Southeast
Idaho will see 1 to 2 inches of rainfall but we are pretty
confident everyone in the region will see a drop or two of
rainfall over this event.

A rather drastic temperature drop will occur Thursday and continue
into Friday. Be in store for 10 for 15 degree cooler high
temperatures tomorrow and an additional 5 to 10 degrees cooler on
Friday. Gradual recovery will occur over the weekend and next week
as high pressure builds into our region and the low exits to the
east. Lingering showers are forecast Saturday for the Eastern
Highland locations before ending Sunday. NP/RS


.AVIATION...There is some convection developing in Nevada
this morning which the HRRR would move into KSUN around 14z this
morning and KBYI about 16Z. Less confidence in timing at KPIH but
little embedded bands in satellite imagery are moving east pretty
quick, gave the NAM the benefit of doubt.  Moisture deepens and
ceilings lower quickly to MVFR tonight 05-07z time period for TAF
sites along the Snake Plain with the first lobe off the H7 low.
There may be a little period early morning with lighter rain, then
the next band develops mid to late morning with a second lobe coming
up, followed by a third Thursday afternoon. RS


.FIRE WEATHER...Strong low pressure system is entering the Oregon
coast this morning and will track through north Nevada/Utah, then NE
into Wyoming. Isolated thunderstorms are expected this afternoon and
again on Thursday. The central mountains and Caribou should be
favored, but with the system moving across this area, forecast is
generally broad brushed with the potential. Models are consistent
with timing of heavier rain developing this evening and the pattern
remaining quite unsettled through about noon Saturday. Moderate to
heavy rain expected for all of Thursday and most of Friday.
Widespread 1 to 2 inches of rain is expected over the Wed night to
Sat afternoon time period and may be locally higher in the
mountains. RS


.PIH Watches/Warnings/Advisories...

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