Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 012246

Area Forecast Discussion
National Weather Service Salt Lake City UT
346 PM MST Thu Dec 1 2016

.SYNOPSIS...A weak storm system will bring light snow to portions
of the forecast area through early tomorrow. High pressure will
move over the region late Friday through early Sunday before a
cold storm system impacts Utah and southwest Wyoming early next


.SHORT TERM (Through 00Z Monday)...A weak storm system continues
to makes its way across northern Utah this afternoon, resulting
in some generally light snow showers. The first wave of the trough
will exit this evening, but will be followed closely by a second
wave entering the area overnight. This will keep enough moisture
and instability around for a chance of snow showers over northern
Utah through the morning. This second wave is expected to merge
with a second trough currently off the California coast Friday
morning, shifting moisture and instability into central and
southern Utah into tomorrow afternoon as the system continues to

The orientation of the California trough will result in a fairly
strong north/northeasterly pressure gradient developing over
southwest Utah tonight and persisting through Saturday morning.
Additionally, there is also expected to be decent cold advection
and good 700 mb flow aloft, conditions that are favorable to
produce a gap wind event for prone areas in Washington county.
Local studies and other guidance would indicate that this will be
a solid advisory level event, so have replaced the going High Wind
Watch with a Wind Advisory.

High pressure centered off the coast is then progged to build
into the forecast area late Friday through early Sunday. A bit of
moisture from a wave moving north of the area will provide enough
moisture for an outside shot of showers over the higher terrain of
northern Utah on Saturday, with no precipitation expected
elsewhere. Temperatures will remain on the cool side through the
weekend, with maxes running in excess of 5F below seasonal
normals. Moisture and instability are expected to increase again
over northern Utah Sunday afternoon ahead of the next approaching
storm system.


.LONG TERM (After 00Z Monday)...Starting the extended period with a
very deep, cold core low dropping through the Western CONUS states
and flattening the weak ridging across the Desert Southwest. With
the associated cold front dropping in from the north, the GFS and
the EC have come into better timing agreement, yet still remain
quite different with how cold the system becomes and how quickly.

The GFS is the colder of the solutions to start out, nearly 5C
colder than the EC solution by Monday morning. A robust cold front
and baroclinic zone becomes tightly packed north to south across
Utah by Monday. A rather narrow band of moisture sets up, as neither
model seems to be excited about high amounts of precip. However,
decent instability associated with the compact frontal passage on
the leading edge of the convergence zone should allow for higher
precip intensity rates. Uncertainty in areal coverage continues with
model runs, so kept a broad brush approach to the PoPs.

Overall feel is that this may be a high PoP, low QPF event given how
cold this system is. 500mb temperatures as low as -37C and 700mb
temps -16C to -18C will span across the county warning area into
Tuesday. By Wednesday, the GFS is quicker to eject the deep wave to
the East while the ECMWF digs the trough axis farther south and
through the four corners area. The question by mid to late next week
will be how quickly do our temperatures rebound and warm, with
daytime highs only reaching the low to mid 20s along the Wasatch


.AVIATION...Expecting the KSLC terminal to see northerly winds
through the overnight hours. Low confidence to see a southerly
switch, so left it out of the TAF. Periodic snow showers into the
overnight hours with MVFR conditions, and brief IFR conditions
possible in heavier showers.


UT...Wind Advisory from midnight tonight to 10 AM MST Saturday for



SHORT TERM...Traphagan

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