Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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327
FXUS65 KSLC 131647
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
947 AM MST Fri Dec 13 2019

.SYNOPSIS...Periods of rain and snow will continue across northern
Utah and southwest Wyoming as a series of weather disturbances cross
the region through Saturday afternoon. A colder weather disturbance
will move southeast through the Great Basin Saturday night through
Sunday, spreading rain and snow to southern Utah late in the weekend.

&&

.DISCUSSION...The weak shortwave trough embedded in the mean near-
zonal flow aloft that contributed to precipitation overnight across
northern Utah is exiting the area, and the associated upper jet has
lifted to the north and east. In the wake of this trough, a
northwesterly flow aloft remains in place, with some cooler air
continuing to spread into the area. With some instability still in
place, moist upslope flow continues to produce showers over the
northern Utah mountains, and some of these showers are spreading
downstream into portions of the Wasatch Back and southwest Wyoming.
Otherwise, expect a net decrease in precipitation and most valleys
including the Wasatch Front will see a bit of a break through at
least early this afternoon.

Warm advection will return by midafternoon, with precipitation
redeveloping again across northern Utah, beginning across northwest
Utah and spreading east. Areas typically favored in southwest flow
should should do well again in terms of precipitation amounts. Some
of the far northern valleys could see precipitation begin as snow or
a rain/snow mix, but continued warming of the airmass should bring
snow levels up tonight for most lower valley locales.

A transition to cold advection commences early tomorrow morning
across northern Utah. Along the baroclinic zone, expect a period of
heavier precipitation where snow levels should come down to valley
floors. However, duration of accumulating snowfall for most of the
Wasatch Front should only be a few hours before the boundary shifts
south out of northern Utah during the afternoon tomorrow.

As the boundary continues moving south, it is progged to strengthen
a bit across southern Utah tomorrow evening/night. This could bring
a period of higher precipitation rates across a focused area along
the boundary for a few hours.

Will have to evaluate the need for additional winter weather
highlights for the valleys and central/southern Utah with the
boundary. Any highlights will likely be impacts-based due to
precipitation rates, as total accumulations are not expected to be
significantly large for most of these areas. Otherwise, short-term
impacts through this afternoon will be limited mainly to the
northern mountains and some higher valleys.

&&

.AVIATION...A lull in precip is expected today at the KSLC terminal
allowing VFR conditions to prevail. This said, periodic cigs at or
below 6000ft AGL will continue to yield local mountain obscuration
of local terrain. Light southerly winds are expected to be
maintained today, with a 40 percent chance of variable west-
northwest winds remaining under 6 knots in the 17-20z window.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Storm Warning until 5 PM MST Saturday for UTZ007>010.

     Winter Weather Advisory until 5 PM MST Saturday for UTZ006.

WY...Winter Weather Advisory until 5 PM MST Saturday for WYZ021.

&&

$$

Cheng/Merrill

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For frequently asked questions about the Area Forecast Discussion
visit...
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