Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 190343

Area Forecast Discussion
National Weather Service Pocatello ID
843 PM MST Sat Feb 18 2017

.UPDATE...The 00Z model updates support some gusty winds
developing again tonight across the South Central Highlands.
Forecast winds from Burley to Pocatello were boosted to 10 to 15
mph with local 20 mph sustained winds on ridge tops and a few
favored canyon areas. The Caribou Highlands and Northern Wasatch
Mountains were included in a Winter Weather Advisory for tonight
through Sunday afternoon. Accumulation of 3 to 5 inches above 6500
feet elevation, including mountain passes will make driving
difficult. RS


.PREV DISCUSSION... /issued 208 PM MST Sat Feb 18 2017/

SHORT TERM...Tonight through Monday night. Moist southerly flow
continuing to produce precipitation across the region. Snow levels
roughly 6500 ft this afternoon, but should fall to about 5500-6000
ft by morning. Heaviest precipitation with this system expected
overnight. Upper trough axis currently over Oregon shifts east
across the region tomorrow with weak cold front. Models showing
weak instability during the afternoon ahead of trough axis so
added slight chance thunder across the entire area, but confidence
low. Will keep Winter Storm Warning for portions of central
mountains and upper snake region above 6500 ft elevation. Brief
break in the precipitation occurs late Sunday into Sunday night
with temperatures dropping to near or below freezing down to
valley floors. Next round of moisture arrives during the day
Monday. Winds increase with influence of strong jet especially
Monday afternoon and overnight. Heaviest precipitation also looks
to be Monday night, though models have diverged significantly on
when/where heaviest precip will fall. Current estimates are for
another round of heavy snow mainly over 6500 or 7000 ft elevation
Monday into Tuesday, and another winter headline may be needed.

LONG TERM...Tuesday through next Saturday. General agreement
between GFS/ECMWF with upper trough deepening into the western
states Tuesday into Wednesday. GFS ensembles lend some confidence in
the evolution of the weather pattern, which is generally suggestive
of higher PoPs. Stronger forcing will come with a shortwave on
Tuesday afternoon into Tuesday night. Precip should continue well
into Thursday, but will see weaker dynamics as jet shifts further
south while the upper trough deepens and shifts eastward. The wave
on Tuesday will also kick up surface winds, particularly over the
mountains. Wind gusts 40 to 50 mph will be common in the upper
slopes with about 30 to 35 mph in the Snake Plain. GFS/ECMWF end
their agreement around Thursday with the ECMWF maintaining upper
trough over the Northern Rockies and GFS a more progressive pattern,
and even suggesting ridging on Friday.  Hinsberger

AVIATION...Deep southerly fetch of moisture being drawn across the
Great Basin and into Idaho today with a split flow pattern in place.
Precipitation having a hard time reaching the ground over the Snake
Plain on account of the southerly flow, but expect better chances of
precip tonight, along with lowering ceilings. MVFR conditions should
be common overnight with IFR conditions at KSUN. Forecast soundings
show southerly winds increasing in the boundary layer and may result
in low-level wind shear mainly at KPIH. Hinsberger

HYDROLOGY...Precipitation remains forecast across the region into
early next week. Main threat of heavy snow remains in areas above
6500 ft, rapidly tapering to rain at valley floors. Precipitation
could be heavy at times tonight along with temperatures remaining
above freezing at lower elevations. A break in the precipitation
will arrive Sunday along with slightly cooler temperatures. Even
valley floors should see temperatures approach or drop below
freezing Sunday night. Another system arrives Monday with another
round of locally heavy precipitation Monday night. Look for
flooding to continue and potentially worsen through this series of
systems. In addition, latest river forecast for the Portneuf at
Pocatello indicates a rise above action stage by Monday. If the
trend does continue, will likely issue a fresh river flood warning
before the weekend is out. DMH


Winter Storm Warning until 5 PM MST Sunday for IDZ018-019-031-

Winter Weather Advisory until 5 PM MST Sunday for IDZ023-025.


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