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FXUS65 KSLC 140452

Area Forecast Discussion
National Weather Service Salt Lake City UT
952 PM MST Wed Dec 13 2017

.SYNOPSIS...The strong and persistent upper ridge will retreat
off the west coast over the next couple of days, allowing weather
disturbances to begin eroding the strong valley inversions, with
the strongest of these storms expected on Saturday.


.DISCUSSION...A shortwave trough continues to dive south through
Utah this evening. Although the inversion remains firmly in place,
it has weakened a bit courtesy of the the cooler airmass that came
with the trough, per the 00Z KSLC sounding. In addition, with a
tightening of the northwesterly gradient helping to bring increased
winds to stir the airmass a bit, there is less saturation just off
the surface as well. As a result, fog has not made much of an
appearance this evening. If fog does redevelop tonight, it would be
well after midnight or closer to tomorrow morning if/when the higher
stratus dissipates. Otherwise, northern Utah valleys will more
likely see visibilities mostly in the 2-5 mile range under stratus

Light snow has also accompanied the trough. However, this snow has
started tapering off north of I-80, which is north of the trough
axis. Lingering light snow will be possible for a few more hours
across the central and southern Wasatch range, Wasatch Plateau,
Uintas, and adjacent valleys.

Finally, northerly winds will continue to increase into southern
Utah through the night. A strengthening surface gradient coupled
with 50kt winds at 700mb (although cold advection is relatively
modest), should yield gusty winds across Washington County tonight,
strongest near canyons.

High pressure builds back into the area tomorrow with inversions
strengthening again. However, this is not expected to be long-lived
as the next trough on Saturday is still progged to bring much colder
air (around -12C at 700mb over much of northern Utah) which will
likely be enough to lift the lid on the inversions.

Updated the forecast mainly to tweak PoP/Sky and reduce fog coverage
for the rest of the night.


.AVIATION...Redevelopment of low stratus and the potential of
dense fog will continue to be the primary operational weather
concern at KSLC this TAF period. Prevailing MVFR conditions are
expected through late tonight in haze/fog, with stratus in the 010-
020 range redeveloping. It is anticipated that the potential for
dense fog formation will hold off until after 08-10z, then a 50%
chance exists for LIFR/VLIFR fog into tomorrow morning.

Light snow fall out remains a potential at times overnight into
tomorrow morning, with any fall out creating light accumulations on
untreated surfaces. Northwesterly winds will weaken through the


UT...High Wind Warning until 9 AM MST Thursday for UTZ019.




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