Area Forecast Discussion
Issued by NWS Pocatello, ID

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000
FXUS65 KPIH 101017
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
317 AM MST Tue Jan 10 2017

.SHORT TERM...Today through Wed night. A much bigger day for
snowfall production as temperatures turn colder from yesterday`s
warm wave. Southwest flow will continue to favor the central Idaho
mountains and the mountain ranges along the Wyoming border. In the
valleys, this will mean heavier snow on the northern side of the
eastern Magic Valley. The colder temperatures also increase the
snow to liquid water ratio. The 24 hour snowfall goes like this: Expect
12 to 20 inches in the Wood River basin, even on the valley
floor. Same goes for the Sawtooth ranges and Stanley basin. These
ranges appear to catch much of the precipitation and leaves very
little for the Lost River and Pahsimeroi basins. The winds and
light to moderate snow in that area probably barely qualify for a
Winter Weather Advisory, so will leave that zone as-is with one in
effect. The Wyoming mountain zones, from Mack`s Inn to Georgetown
should get hit pretty hard, with 10 to 20 inches even in the
valley floors like Teton Valley, Swan Valley, and the Bear Lake
basin. The north end of the Eastern Magic Valley will get hit
pretty hard for a low elevation location due to the upslope effect
in the south to southwest flow. Expecting 24 hour snow of 6 to 12
inches in the area for Shoshone, Richfield, and Carey. But even in
the south where the downslope should cause something of a
precipitation shadow will receive 3 to 6 inches of new snow.
Finally, the Snake River plain looks like 2 to 6 inches. The trend
is for moderate to heavy snow this morning, with a bit of an early
afternoon lull, and then an evening spike upwards again that
continues through the late night hours. Have added the
southcentral highland because widespread snowfall in excess is
expected, although mainly east of the Interstate 84 corridor.

For Wed, snowfall appears to be decreasing rapidly during the
afternoon and continuing much light overnight Wed night. That 24
hour period appears to have half of what is expected today and
tonight, as a rough estimate. Most of this will drop Wednesday
morning.

The other main forecast problem is the strong winds, which will
hamper snow removal efforts with heavy drifting. Winds in the
Snake River plain will increase during the afternoon and continue
through the overnight hours.

A third problem is that MOS guidance has been way too warm for the
last several days, and it appears to continue that way, at least
for this period. Have used a bias-corrected guidance. While
temperatures may get slightly above freezing for the lower
elevations in the south, expect the freeze-thaw to continue below
6000 feet elevation. Messick

.LONG TERM...Thursday through Tuesday.

Snow will be ending across the region on Thursday. Any additional
snowfall amounts will be light and probably under an inch. High
pressure settles in through the weekend and into early next week.
Expect cold weather across the region over the weekend, although
probably not nearly as cold as the previous cold snap. Still,
overnight lows in many places will be near zero or below zero.
Models are showing another healthy storm in the Pacific which will
be slamming into Washington for early next week. Although it looks
like the high pressure over the region will deflect much of the
moisture north initially. Wouldn`t be surprised if we get back into
a somewhat active pattern by midweek.

Valle

&&

.AVIATION...Atmospheric river is alive and well across the region.
This is giving us a mixed bag of ceilings with the lower ceilings
existing when the showers move through. Winds remain brisk as well.

Valle

&&

.HYDROLOGY...Rain on snow continuing at many elevations below 6500
feet MSL where multiple public reports of nuisance flooding of roads
and basements have been received. Little cooling is anticipated over
the next 48hours at elevations below 6000 feet MSL with another
round of lower elevation rain and higher mountain snowfall expected
tonight through Tuesday. Thus the Areal Flood Watch has been
converted to a Flood Warning. It is easier to list those counties
NOT under a flood threat: Custer, Clark, Fremont, and Teton.

Potential Flooding is possible on the Wood River in Hailey due to
a temporary damming by a snow avalanche slide that has blocked the
river bed. Also, there is a park in Challis still affected by
flooding.

With the fluctuation in temperature, we may also be looking at
continued issues for ice jam flooding.  See the Hydro Outlook and
Flood Advisory products for more specific information on ice jam
issues. Huston
$$

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 AM MST Wednesday for IDZ020-021-
032.

Winter Storm Warning until 6 AM MST Thursday for IDZ018-019-023-
025-031.

Winter Storm Warning until 5 AM MST Wednesday for IDZ022.

Winter Storm Warning until 5 AM MST Wednesday for IDZ017.

&&

$$



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