Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 172319
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
419 PM MST Fri Nov 17 2017

.SYNOPSIS...A cold upper level trough will cross northern Utah
early this evening, with high pressure aloft spreading across the
region this weekend. A weak weather disturbance will graze northern
Utah Monday night, followed by strong high pressure aloft
returning midweek.

&&

.SHORT TERM (Until 00z Tuesday)...The cold core upper level trough
tracking east across the northern Rockies/northern Great Basin
late this afternoon will exit the area by late this evening. A low
amplitude upper ridge will replace the trough this weekend.

Convection has become increasingly organized along the near 700mb
baroclinic zone surging south through central Utah late this
afternoon. Rapid mid-level cooling has created a more unstable
air mass, which combined with the strong low-level forcing and
divergence at the entrance region of the jet has spawn the fairly
deep convection over central Utah. This convection will likely
fall apart as the boundary settles into extreme southern Utah
early this evening. Low-level forcing will remain fairly strong,
though support from the upper trough will wane as this feature
races off to the east and the upper jet moves south and east of
the forecast area.

Instability showers will persist across northern Utah within the
mid-level cold pool early this evening. Additional accumulations
of snow will be minimal, so will allow the winter weather
advisories to expire at 00 UTC. Increasing dynamic subsidence
behind the exiting trough along with rapid drying/warming aloft
will end any threat of showers during the evening.

Clearing skies, decreasing winds and abundant boundary layer
moisture are the recipe for fog development later tonight. The
mostly likely areas for fog will be the northern valleys where
substantial amounts of precip, including some accumulating snow
occurred today. Will mention areas of fog in the Cache valley,
the Wasatch mountain valleys and the northern Wasatch Front from
roughly Ogden northward late tonight through Saturday morning.
Will keep the areal coverage of fog over the northwest desert and
extreme southwest Wyoming some more limited as winds may stay
somewhat elevated until late tonight.

A low amplitude upper ridge will expand across the region in the
wake of the exiting trough this weekend. Heights will lower
slightly on Monday ahead of a fast-moving shortwave scheduled to
arrive over northern Utah after the end of the short term forecast
period.

.LONG TERM (After 00Z Tuesday)...The global models have evolved a
bit in the extended with regards to timing and track of the
shortwave anticipated to drop south through the Great Basin early in
the week. The GFS and the EC have both trended slower with the wave,
as well as slightly more north by early Tuesday. Both solutions are
amplifying the ridge across the desert southwest and thus the
shortwave is being stretched out and opening into a wave sliding
down the east side of the Rocky Mountains.

As the jet orients itself northwest to southeast sliding down the
east side of the ridge, some moisture is associated with a weak
baroclinic zone dropping southeast through  far northeast
Utah/southwest Wyoming. At this time, the upper level front is
pretty disorganized and the best moisture window is brief. With this
package, made some minor upward trends in PoPs to account for the
favorable northwest flow as the zone drops southward.

With a ridge of high pressure building in by mid-week, extended
models keep this pattern going through the Thanksgiving Holiday and
into next weekend. Some question as to how this ridge will weaken
and break down is uncertain, and models are not really consistent.

&&

.AVIATION...VFR conditions are expected at the SLC terminal through
the evening, with cigs expected to rise above 6000 ft AGL by 00Z as
showers move out of the area. Northerly winds are expected to shift
to the southeast between 03Z and 05Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory until 9 PM MST this evening for UTZ013-020-021.

WY...None.
&&

$$

SHORT TERM...CONGER
LONG TERM...DEWEY
AVIATION...TRAPHAGAN

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php



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