Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 141946

Area Forecast Discussion
National Weather Service Pocatello ID
146 PM MDT Thu Sep 14 2017

.DISCUSSION...Currently monitoring a developing low pressure
system that will be dropping southward into the central Idaho
mountains tonight. Models show batch of afternoon showers and
isolated thunderstorms progressing east tonight ahead of a cold
front. Expect drier air to work into the area behind the cold
front for a time. As the low pressure system strengthens, expect
moisture to work back into the central Idaho mountains from
Montana late tonight and early Friday morning. Snow levels will
gradually fall from 10,000ft to around 8000 feet Friday morning
across the central mountains. Expect precipitation to pick up
during the day on Friday across the central mountains as the low
matures and moves through the mountains. Expect breezy conditions
across the Snake Plain, Magic Valley and southern highlands on
Friday, possibly warranting a wind advisory if we can get enough
breaks in the clouds. By Friday night, the low will move through
the upper Snake highlands bringing lowering snow levels and a
batch of wrap around precipitation through with it. Snow levels
will fall to 6000-6500 feet across the central mountains and upper
Snake highlands. Ground temps appear too warm for accumulating
snow on road surfaces, however could see some light accumulations
especially above 7000 feet. Don`t be surprised to see light snow
accumulations on grassy and elevated areas around Island Park,
Monida Pass, Willow Creek summit, and Galena Summit. Although
possibly important to those with backcountry interests, probably
not significant enough to warrant an advisory. This system will
slowly exit the region during the day on Saturday with
precipitation being slow to end across portions of the central
mountains into the eastern highlands.

Looks like we have dry weather for Saturday night and Sunday with
frost possible for portions of the Snake Plain by Sunday morning.
The next cold front arrives on Monday. This front will be
accompanied by a line of showers as it marches through the region.
Expect showery and chilly weather for Tuesday through Thursday as
another strong low pressure system builds into the Pacific
Northwest. High elevation snow will be possible once again,
especially above 6500 feet.



.AVIATION...Showers and isolated thunderstorms reign supreme this
afternoon as our storm is moving into our part of the world. So far
even with heavier rainfall in some areas, we are only see VFR
weather. Expect though as we get even more widespread precipitation
developing, the potential for MVFR/IFR weather due to lower ceilings
and intensity increases. We maintain -SHRA VCTS through this evening
and -SHRA overnight at all TAF sites.  The expectation is that a dry
slot works up the Snake Plain late tonight/Friday and ends
precipitation at KBYI and KPIH, and at least switching KSUN and KIDA
to VCSH. There are some variations in how strong the winds MIGHT
get, but for now for the 2 valley sites we are expecting 15-25kt
winds with gusts to 35kts possible. If the higher end forecast pans
out, sustained winds of 20-30kts are possible with higher gusts.
KIDA is right on the edge of this dry slot so it`s possible they
stay rainy with low ceilings. During the afternoon, rain and
mountain snow shifts south a bit so expect -SHRA to return/pick up
again at KIDA, KSUN and KPIH. Snow levels will stay high enough at
this point to not affect KSUN or KDIJ. Speaking of KDIJ, current
trends indicate once the rain moves in, it stays there through
tomorrow with lower ceilings. Keyes


.FIRE WEATHER...Our big pattern shift is underway. Showers and
isolated thunderstorms increasing this afternoon.  Rain and mountain
snow continues overnight across all of eastern Idaho, with snow
levels dropping to 6500-7500ft across zones 475 & 476, and around
8000-8500ft in zone 422. Elsewhere, they only drop to 9500-10500ft.
A dry slot works up the Snake Plain, ending precipitation for a time
across 425, 427, 413 and the southern half of 410. Do expect winds
to really pick up with gusts of 20-35 mph common especially across
425,427 and the southern end of 410. Tomorrow afternoon, rain and
snow will shift south and east with most of the precipitation will
fall across 410,411,422,475 and 476. Snow levels continue to drop
tomorrow with snow levels ranging from 6000-7500ft across the
central mountains to 8000-9500ft along the Wyoming border. The low
finally shifts east of us Saturday with showers completely out of
here by late afternoon.  We see a short break Sunday and Monday
morning, before the next storms begins to slowly trek across the
West. While details in terms of who gets how much precipitation
aren`t there, this looks to be another fall-type storm and could
even bring colder temperatures our way.  In fact, this pattern of
colder/wetter than normal weather is potentially with us for the
next 1-2 weeks. Keyes



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