Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 112243

Area Forecast Discussion
National Weather Service Salt Lake City UT
343 PM MST Mon Dec 11 2017

.SYNOPSIS...Strong and persistent high pressure aloft will remain
the dominant weather feature across the western states through the
work week.


.SHORT TERM (Through 00Z Friday)...The broad ridge remains parked
over the forecast area this afternoon. For many locations across
Utah and southwest Wyoming, this is result in dry and mild
conditions with light winds. However, valley inversions continue
to strengthen over northern and central Utah resulting in poor air
quality, cold temperatures, and some persistent areas of fog and
stratus, primarily over the Cache Valley, Bear Lake, and in some areas
near the Great Salt Lake, including portions of Salt Lake and
Davis counties. Even outside of the fog, urban haze is resulting
in reduced visibilities in many valley locations.

The ridge will continue to be the dominant weather feature through
Friday, though the ridge axis will track back west, eventually
moving over California by midweek. Shortwave energy moving over
the ridge on Wednesday will increase clouds and northerly flow
somewhat, but this will not nearly be enough to weaken the valley
inversions. It will, however, cool temperatures slightly away from
the inversions.

.LONG TERM (After 00Z Friday)...Strong upper level ridge persists
into Friday as an upstream trough moves into the Pacific Northwest.
This will keep the inversion and, the continuation of poor air
quality, in place across northern Utah valleys into Friday. The
operational GFS, ECMWF, and Canadian all drive a cold front through
northern Utah Friday night or early Saturday morning. The cold pool
with this system, as currently forecast, would be strong enough
to scoop the valley inversions across northern Utah. The ECMWF and
Canadian keep the cold pool a little further north and the ECMWF
trended moreso that direction with this morning`s run. There is
still the potential for the storm track to stay too far to the
north to clear out the inversions, but the current operational
runs are promising. Best upper level support stays north of
northern Utah and mid level baroclinic zone is, at best, very
weakly frontogenetic, so at this time this system does not look
like a significant precipitation producer. Southern Utah will
continue to see mostly sunny skies and above normal temperatures
in most locations.

Behind this system ridging quickly builds back into the region
which should bring temperatures back to near or slightly above
normal across northern Utah late this weekend into early next
week. Temperatures across southern Utah are expected to be 5-10
degrees above normal late this weekend into early next week.


.AVIATION...At the SLC terminal, IFR conditions are expected to
persist through the evening, though there is a slight chance of an
improvement to MVFR conditions between 23Z and 02Z. Dense fog, with
visibilities 1/4 mile or less, should return sometime overnight;
exact timing of this return is low confidence, but the most likely
timeframe is 05-09Z.




SHORT TERM...Traphagan
LONG TERM...Graham

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