Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 241608

Area Forecast Discussion
National Weather Service Pocatello ID
908 AM MST Tue Jan 24 2017

.UPDATE...Radar continues to show mainly light snow from the Upper
Snake/Yellowstone region southwest to the Eastern Magic Valley
and including the surrounding foothills. Some indication of
surface convergence with circulation seen in radar loop near Idaho
Falls in association with shortwave feature aloft. Have made some
minor adjustments to grids for today to concentrate additional
snowfall in these areas through today, where orographics in the
wrap around moisture are expected to be the dominant forcing for
today. Additional 2-3 inches of accumulation through tonight seem
reasonable with consensus that snow will taper through today. Will
keep the headlines in place while snow continues. DMH


.PREV DISCUSSION... /issued 223 AM MST Tue Jan 24 2017/

SHORT TERM...Today through Thu night. Surface low continues to
move away from the Gem State and significant snowfall will finally
terminate during the day today. With some continued wind, have
extended the Winter Storm Warnings through 3 PM today. There is a
significant wind shift to northerly air flow. This will cause
temperatures to turn cold rapidly and bring back below normal
temperatures for this time of year...even below zero for places
like Stanley Basin, the Round Valley (Challis), and Teton Valley
(Driggs). Even the upper Snake River plain will see single digit
overnight lows tonight. Weak shortwaves moving through this
northerly flow will continue to provide cloudiness and a low level
threat of snow on north-facing slopes. This would mean enhanced
snow along the Snake River corridor and in the southern and
eastern highlands, while places such as the Wood River Valley
would be in a precipitation shadow. Serious fog will probably not
be seen until there is a significant reduction in cloud cover on
Thu night. Messick

LONG TERM...Friday through next Tuesday. The GFS and ECMWF continue
to show an amplified ridge across the NW coast with a dry and cold
northerly flow over SE Idaho. The GFS and ECMWF continue to show a
disturbance topping the ridge Sunday night (about 6 hours slower
than last nights progs) however the GFS is now more aggressive as
the wave digs SSE into Montana Monday morning with attending
precipitation impacting the divide region whereas the ECMWF keeps
the passing wave further north and east with no impacts. By Tuesday
night, the next Pacific low takes up position off the NW coast and
the GFS is responding with warm over-running precipitation over the
CNTRL Idaho mountains and divide region whereas the ECMWF has a more
robust ridge which was directing all the precipitation into Canada.
I tilted the forecast toward the GFS on both systems. Huston

AVIATION...Upper low currently traversing the region early this
morning with ongoing MVFR CIGS in light snow at all terminals. Some
weak troughiness will linger over the region today as the main low
shifts ENE through Wyoming. The models continue to show some low
level convergent flow sustaining ongoing light snow and MVFR/IFR
CIGS at KBYI, KPIH, and KIDA while both KSUN and KDIJ fall on the
periphery of the main action. Some improvement may be seen tonight
as the flow aloft becomes NW, however an embedded disturbance may
keep the threat of MVFR CIGS going at KBYI, KPIH, and KIDA. Huston


Winter Storm Warning until 3 PM MST this afternoon for IDZ017-


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