Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 141122

Area Forecast Discussion
National Weather Service Salt Lake City UT
422 AM MST Tue Nov 14 2017

.SYNOPSIS...A weak upper level trough will graze northern Utah
today, bringing a threat of light precipitation to far northern
Utah this morning. Dry weather is expected statewide on Wednesday
as an upper level ridge briefly builds over the area. This will
be followed by a potentially stronger and colder trough Thursday
into Friday.


.SHORT TERM (Through 00z Saturday)...The southern fringe of a
weakening trough that lifted north into southern Alberta over the
last 12 hours is attempting to impinge into far northern Utah at
this time. H7 analysis depicts a modest thermal gradient
associated with this, though reflection remains quite shallow and
relegated to elevations below H5 due to the upper support
remaining well north of the area. Still, the modest low level lift
associated with the shallow front coupled with a some jet support
aloft has allowed scattered showers to develop along the boundary
(currently over the Raft River`s of far NW Utah NE into southern
Idaho). This band of scattered showers will gradually shift east
across the UT/ID border region this morning prior to dissipating
this afternoon as heights build rapidly in wake of the wave`s
departure. No precip expected south of roughly Brigham City,
though temps across the north should cool some 5+ degrees vs.
yesterday`s highs as the surface boundary has already slipped
through KSLC and weak CAA aloft is noted.

The upstream pattern is currently in the process of reloading in
the Gulf of AK, as the next upper low deepens off the BritCol
coast. As the heights begin to rebound this afternoon downstream
of the trough, flow will back more southwesterly aloft allowing mid
level warm advection to shift over the eastern Great Basin
through Wednesday and into the overnight hours. Temps by Wed
afternoon should once again push 10 degrees above climo for most

The aforementioned trough remains poised to slowly shift ESE
across the Great Basin Thu-Fri, bringing a marked change to
the sensible weather experienced as of late. Of note, confluent
flow over the southeastern Pacific in advance of this will aid to
develop a narrow but evident deep moisture tap that will aid to
prime precip production both in advance and coincident with trough
passage. Although timing and subtle trough evolution differences
continue to exist in the globals, all point towards a much cooler
and overall wetter period through this time, especially Thu
afternoon through Friday morning. Subtleties regarding trough
progression and extent of CAA coincident with the available
moisture continue to exists, but attm things point toward minimal
cold season valley impacts (though some light snow is likely),
with modest mountain accums across northern/central Utah. Further
details should begin to be refined over the next 24hrs or so.

.LONG TERM (After 00Z Saturday)...Model to model discrepancies in
timing have a significant impact on the first portion of the long
term forecast. The 00Z GFS would indicate the cold Pacific trough
will have departed the area at the end of the short term forecast.
The slower EC (which has been slower for a number of runs now) would
hang on to precipitation through 06-08Z at least across portions of
the CWA...and this precipitation could be heavy at times based on
this solution. For now, introduced higher pops in the 00Z-12Z
Saturday timeframe to incorporate the potential EC solution.

Broad ridging is expected to build in to the area in the wake of
this system. Given the time of year and significant mid-level warm
air advection, expect inversion conditions to develop Sunday and
Monday. This should keep temperatures from warming as fast as much
of the model guidance indicates across the valleys of
Utah...especially if there is any ground snow.

Major model to model discrepancies occur with the next system,
expected to impact the West early next week.  Anything from a brush
by to the south to a major storm impacting much of Utah is currently
forecast by the global models.  For now, introduced pops for this
period as a compromise.


.AVIATION...North to northwest winds will continue at the SLC
terminal through the day. Winds may be light and variable for a time
between 12-14Z but should increase again after 14Z.





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