Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 201617

Area Forecast Discussion
National Weather Service Pocatello ID
917 AM MST Mon Feb 20 2017

.UPDATE...Have made a few minor tweaks to forecast for today,
mainly to adjust to early QPF/Snow trends. Band of weak showers
moving northeast across forecast area. Short term forecast trends
are for region to become more widespread into early afternoon with
localized stronger embedded activity. Temperatures and snow levels
look consistent with forecast, so overall minor adjustments to QPF
had little effect on expected snow totals. Highest snowfall still
on target for the higher elevations of the central mountains.
Surface low over OR/WA progged to shift northeast into western MT
through the day today, putting favorable surface gradient in line
with increasing upper level winds and snake plain terrain.
Therefore nudged winds up slightly this afternoon in line with
guidance, though isolated convective enhancement this afternoon
could be a nudge upward for gust potential. DMH





.PREV DISCUSSION... /issued 237 AM MST Mon Feb 20 2017/

SHORT TERM...Today through Wednesday night.
Another moist Pacific storm is expected to begin lots of moisture
and warm temperatures through Tuesday. Have issued winter storm
warnings above 6500 feet for the central mountains and a winter
weather advisory above 6500 feet for the Upper Snake River
Highlands. Lower elevations may start out as snow today but will
quickly change to rain below 6500 feet. Areal and river flooding
will remain a threat as well through the short term. More rain is
likely in Minidoka County where flooding remains widespread with
very warm temperatures through Tuesday. A cold front will move
through Idaho on Tuesday and temperatures will drop substantially
Tuesday night with high temperatures Wednesday back to near or
slightly below seasonal normals for late February. Will also see
windy conditions ahead of and behind the cold front Tuesday and
Tuesday night. May need wind advisories on Tuesday but will hold
off on issuing any at this time.

LONG TERM...Thursday through next Monday. The GFS and ECMWF
remain fairly similar on the broad strokes but differ with some of
the details as two waves drop SSW across WRN Canada into the NW
Thursday and again Friday helping to maintain a broad cool upper
trough and a chance/slight chance mention of snow across the region.
By Sunday, a mostly dry Canadian trough sweeps through the region
ahead of another Pacific trough dropping into the NW late Sunday
into Monday. At this point the models diverge on the handling of
this system with the ECMWF driving most of the energy and
precipitation south along the coast whereas the GFS pushes it inland
under a much more progressive NNW flow regime. Either way, a chance
mention of snow across the region is a reasonable response. Temps
will run at or below normal through this period. Huston

AVIATION...A flat ridge was positioned over the area early this
morning resulting in mostly VFR SCT conditions as the next Pacific
trough was advancing toward the NRN California coast. Numerical
models suggest increasing warm-frontal precipitation across the
region this morning followed by a straight shot of sub-tropical
moisture embedded in SW flow this afternoon and continuing through
the night. CIGS will deteriorate with the incoming moisture
generally running with low VFR CIGS in the Snake River Plain and
occasional MVFR and tempo IFR conditions in rain. KSUN will likely
see IFR/LIFR CIGS through at least Tuesday eve/Wednesday before
seeing some relief. Model cross sections show DIJ saturated through
a fairly deep layer throughout the forecast period but the reality
is they have not been of much help. Will probably float along with
MVFR CIGS there until something looks more definite. Huston



Winter Weather Advisory until 3 PM MST Tuesday for IDZ019.

Winter Storm Warning until 3 PM MST Tuesday for IDZ018-031.


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