Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 142206

Area Forecast Discussion
National Weather Service Salt Lake City UT
306 PM MST Thu Dec 14 2017

.SYNOPSIS...High pressure will build into the area through Friday.
A Pacific system will cross the area Saturday. High pressure will
build into the area once again Sunday into Tuesday with another
storm expected Wednesday.


.SHORT TERM (Through 00Z Monday)...Afternoon water vapor and H5
analysis depict a highly amplified long wave pattern over the CONUS,
with the persistent upstream ridge (oriented along the Pacific
coast) being the dominant feature locally. Over the next 36 hours
building heights combined with warming aloft (H7 temps likely
climbing another 4-5 C) will aid to enhance inversion conditions
once again across the northern/central valleys/basins, but relief is
in sight.

Good agreement exists that the trough currently noted in the Gulf
of Alaska will roll over the top of the ridge Friday further
retrograding the mean ridge position, with this allowing it to
rapidly drop SE across the Great Basin region later Friday night
through Saturday. Although this trough will be splitting, the
attendant cold front and associated CAA will allow full mixing of
the stagnation in place while bringing light snowfall to much of
northern/central Utah Saturday into the nighttime hours.

Dynamically speaking this trough is not impressive for normal Utah
cold season standards, but increasing low level instability
coincident and behind the near H7 thermal gradient should be
sufficient for light snowfall through axis passage for most all
areas along the I-15 corridor and mountain areas. SREF plumes
along with deterministic output points towards roughly 1-3"
falling along the Wasatch Front, and up to 6" in the mountains
favored by NW flow (focused Wasatch). This should pose some road
impacts due to the cold surface conditions that will be in place,
but those details will be hashed out tomorrow. This trough will
gradually exit the region by Sunday with lingering snow showers
gradually waning, this as low amplitude ridging builds back in

.LONG TERM (After 00Z Monday)...A few showers may linger as the
trough gradually moves away from the area Sunday evening.
Northwest flow will remain across the area in the wake of the
trough, with sufficient deep moisture across far northern Utah to
allow for at least occasional orographically enhanced snowfall for
portions of the far northern Utah mountains. This will continue
until a warm front crosses the area Wednesday and southwest flow
brings warmer, drier air to the entire state.

Much of the global guidance indicates a VERY cold system will
impact the area Wednesday into Thursday. The consensus of the
global guidance indicates the associated strong cold front will
cross the state Wednesday into early Thursday with 700mb
temperatures falling to -18 to -20C across northern Utah. This
would change any precipitation associated with the front to snow
quickly. Right now, this system doesn`t look especially prolific
for widespread, heavy precipitation but it does look quite cold.


.AVIATION...Light northerly winds at the SLC terminal are expected
to shift to the southeast around 02-04Z. It is likely that
visibilities will drop to MVFR levels between 02Z and 09Z, but there
is only a 10 percent chance that visibilities or ceilings drop to
IFR levels or below through 12Z.





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