Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 172052

Area Forecast Discussion
National Weather Service Pocatello ID
152 PM MST Tue Jan 17 2017

.SHORT TERM...Tonight through Thursday night.

High pressure remains in control of the weather today producing
continued cold weather across the region. This high will begin to
move east Tonight as the next storm moves onshore. Expect to see
high clouds drift through the region late which might help to keep
temperatures up relative to the past few days. Winds will pick up
some across the central Idaho mountains which may help break some of
the inversions that have set up in Challis and Stanley where
ridiculously cold temperatures have been reported.

Snow will arrive in the Sawtooth range around noon and begin to
advance down the range into the Magic Valley by evening. Looks like
there will be enough warm air aloft to allow some snow to either
change to rain or freezing rain from Twin to Burley to the Coldwater
and Malta areas. The axis of the heaviest precipitation set up from
Stanley to Hailey to Burley and west. Outside of a few showers, the
main batch of snow will have a very difficult time moving east or up
the Snake Plain until Thursday. Potential for very large snow
amounts exists. Right now, expect the heaviest snow to fall along
the Sawtooth Range to Shoshone. The potential is there for large
amounts in Burley and Malta as well, however, rain may eat away at
the amounts. Expect 5 to 10 inches from Bellevue to Stanley with up
to 15 inches possible along mountain tops. Areas around Shoshone and
Richfield could see up to 10 inches because of their location in the
heavy precipitation axis and model soundings say they will stay all
snow during this event. Snow forecast for Burley and Malta areas is
tough because of the warm layer. Best guess right now is for 3 to 7
inches but could be less or more depending on warm air. Am not
concerned about rain on snow flood potential across the Magic Valley
at this time because there will probably be enough cold air in place
to keep the bulk of the precipitation in the solid form. Although if
it were to remain all rain, then, yes that would be a very serious
problem. Will upgrade all watches to warnings. Travel will be very
tough. Note, these numbers are a 2 day total starting Wednesday
afternoon through Thursday evening.

Elsewhere, amounts will be much less as much of the energy with this
system is quickly diving south. By the time moisture finally works
east, much of the intensity will have weakened. Most areas are
looking at 1 to 3 inches east of a line from Challis to Arco to
American Falls to Preston. And this is a 2 day total with the
heaviest snow falling Thursday afternoon and evening. Will hold off
on an advisory at this time. If later forecasts support heavier
amounts, may end up issuing advisories.


.LONG TERM...Friday through next Tuesday night. The GFS and ECMWF are
remarkably similar until the next significant storm on Sun night and
Mon. There is a greater threat of precipitation that started on the
17/00Z run of the extended models that has continued this morning.
However, it is an almost indistinguishable feature moving through a
ridge and thus should not amount to much in the way of
precipitation. The strongest storm of this period arrives during the
afternoon Sun in the western and southern zones, and is generally
much wetter on the GFS, especially for the central Idaho mountains.
The ECMWF continues with precipitation an additional 24 hours with a
slower exit of this storm. Have mostly bought into the broader-
brushed ECMWF which lately has been performing better with its
temperatures. There have been slight biased towards the GFS, but
starting with the ECMWF as a base. Messick


.AVIATION...Fog and stratus cleared early today, which begs the
question will it appear at all tonight and Wednesday morning.
Vertical profiles indicate that it will remain pretty dry in the
west of the forecast area, and so do not expect KBYI or KSUN to have
any problems. This is mainly true due to an approaching front that
is stirring up the surface boundary layer with stronger wind and
some sky cover. These winds and the cover will not reach the east,
and so would expect KIDA to continue with some trouble tomorrow
morning. The stratus lasted only a few minutes at KDIJ and do not
expect a return. This leaves KPIH with the toughest forecast.
Have decided to go against MOS predictions, which have been pretty
horrible for KPIH lately, and brought in only mist-level fog very
late in the forecast, with an early break out as the wind
increases. Messick


.HYDROLOGY...We have converted the Flood Warning for eastern
Custer County in central Idaho and central Butte County in
southeastern Idaho to a Flood Advisory, until 930 AM this Friday,
based on coordination with on-scene emergency management officials.

The Flood Advisory for the town of Challis also continues until
Friday. This was also based on coordination.


Winter Storm Warning from 3 PM Wednesday to 9 PM MST Thursday
for IDZ017-022.

Winter Storm Warning from 11 AM Wednesday to 9 PM MST Thursday
for IDZ018-031.


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