Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 232315

Area Forecast Discussion
National Weather Service Salt Lake City UT
415 PM MST Tue Jan 23 2018

.SYNOPSIS...High pressure will return midweek before a fast
moving storm system impacts the area Thursday into Friday morning.
High pressure is expected to return for the upcoming weekend.


.SHORT TERM (Through 00Z Saturday)...Rising heights and mid-level
warm air advection signal the arrival of high pressure across the
Interior West. Satellite imagery indicates snow cover remains in
place across nearly all of southwestern and west central Utah this
afternoon outside of the lowest elevations near St. George. This
snow cover has kept many locations from realizing expected high
temperatures this afternoon. Anticipate these areas will cool well
below most available model guidance this evening into tonight
under mainly clear skies. Many areas from Milford to Delta to
Cedar City are in for quite a cold January night. Patchy dense fog
will be possible across the Cache Valley and the Wasatch Back

Expect southwesterly flow to increase through Wednesday afternoon
and evening, though many of the valley locations will remain
inverted through this time. Any remaining inversions should mix
out Wednesday night into Thursday morning ahead of the cold front
as winds increase further.

The previously mentioned cold front has trended into a rather
blase event over the last few model runs. Much of the global model
guidance feature a weakening trough entering the state Thursday.
While the airmass in the wake of the cold front is quite cold,
dynamic forcing is limited. At this time, it appears the cold
front will move through the state Thursday morning into Thursday
afternoon with a limited frontal band of snow to valley floors.
With marginal west to northwest flow, expect a period of
orographic enhancement in favored mountain areas, but the latest
runs of both the GFS and the EC indicate a brief window of

As the backside of the trough crosses the state Friday, expect
another round of snow showers across mainly the higher terrain of
Utah. Snow totals from this portion of the trough are expected to
be low as well.

.LONG TERM (After 00Z Saturday)...Models are in better agreement
today for the start of the long term period. Both now indicate a
warm advection northwest flow will be in place across the nrn CWA
with the WAA becoming stronger on Sat lasting into Sun. The GFS
continues to show more moisture in this flow extending farther
south, with a little better chance of snow than the EC, but the EC
has come towards the GFS solution in this new 12z run.

Even with this more robust WAA pattern, model qpf remains low and
spotty. These can end up being high pop low qpf events but for
now seeing as this is day 4, have kept pops on the low side but
did expand them to cover more of the nrn CWA Fri night thru Sun.

Models are now also in agreement on short wave ridging bringing
dry conditions Sun night thru Mon. The next deeper Pac trof is
forecast to start moving into the northwestern states Mon night
with a weak leading short wave crossing the CWA early Tue. The
main trof arrives Tue night and would bring a band of snow along
the cold front to about the nrn 2/3 of the CWA, as currently
depicted in the GFS. The EC is similar but somewhat slower altho
both are quite cold past day 7. Confidence is still not that high
in the guidance for this time frame so just raised pops about 10
percent above climo for Tue night.


.AVIATION...The SLC terminal will see VFR conditions throughout the
night. The clouds around 6000 ft are dissipating and any cigs that
form will be well above that level. Northerly winds are expected to
return to the southeast between 03Z and 05Z.





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