Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 211016

Area Forecast Discussion
National Weather Service Salt Lake City UT
416 AM MDT Fri Apr 21 2017

.SYNOPSIS...A cool northwest flow Friday will be replaced by high
pressure on Saturday bringing a warming trend. An active pattern
is expected for next week, as a series of storms systems are
forecast to pass through the region.


.SHORT TERM (Through 00Z Tuesday)...Northwesterly flow aloft
prevails across the Great Basin early this morning, in the wake of
a departing shortwave trough currently crossing the central
Rockies. Cold air aloft is allowing for modest instability over
the relatively warm waters of the GSL (as well as Utah Lake), and
continue to see showers develop and move downwind into adjacent
portions of the Wasatch Front. These have exhibited a gradual
weakening trend over the last couple hours, and expect these to
diminish by mid morning.

Mid level ridging along the Pacific Coast will build inland today,
before translating eastward across the Great Basin tonight through
Saturday. This ridge will move east and weaken Saturday night,
allowing a much more active westerly flow to spread inland
beginning Sunday, with when the first in a series of waves is
forecast to translate inland and across the forecast area. This
first wave will impact mainly northern Utah bringing a chance of
showers Sunday afternoon and Sunday evening, followed by a strong
jet penetrating inland Monday and bringing a chance of valley rain
and high elevation snow to areas generally north of I-80 Monday.

.LONG TERM (After 00Z Tuesday)...Global models in general agreement
with a moist pacific flow through Wednesday, with a series of upper
level disturbances sliding across the Great Basin, producing
precipitation across northern Utah Monday night and across the vast
majority of the forecast area Tuesday and Wednesday.  With a rather
moist air mass and strong upward forcing due to upper level
disturbances and 120 knot upper level jet nosing into Great Basin,
significant precipitation amounts will be possible, especially
Tuesday night and Wendesday.  Snow levels generally in the 7,000 ft
to 8,000 feet range Tuesday and Tuesday night will lower on
Wednesday as a cold front crosses the region.

Model differences emerge on Thursday as GFS deepens trough over
eastern Great Basin, eventually developing a closed low.  ECMWF and
Canadian both hint at a bit of mid level riding on Thursday, then
deepen trough over Eastern Great Basin on Friday.  Given that
majority of GFS Ensemble solutions resemble ECMWF and Canadian
solutions, will lean toward them.  Given divergence in solutions,
confidence is still somewhat low at this time, so will essentially
retain existing forecast.  With cold air advection from late
Thursday into Friday, snow levels could lower to bench levels, 5000
feet, across northern Utah.


.AVIATION...Predominately VFR conditions will prevail at KSLC
through TAF period, though a period of MVFR ceilings with a rain
and/or snow shower will be possible through 14Z, as a few lake
effect showers will be scattered about the area.  Ceilings below
7,000 feet are expected through around 18Z.  Could see a period of
variable winds through 14Z, then mixing should promote northwest
winds with some increase in speed.





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