Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 091346 CCA

Area Forecast Discussion
National Weather Service Salt Lake City UT
643 AM MST Fri Dec 9 2016

Corrected Aviation Discussion

.SYNOPSIS...A persistent and quite moist westerly flow aloft will
generate significant precipitation across much of northern Utah
and southwest Wyoming into early next week. Southern Utah will
remain south of the storm track until late in the weekend.


.SHORT TERM (Through 00Z Tuesday)...The mid-latitude zonal
pattern extending from the eastern Pacific the east across the
CONUS will persist through at least early next week. A substantial
moisture plume has already been tapped by the westerly, with this
moisture taking aim on the western states the next several days.

A series of closely spaced shortwaves embedded in the fast moving
westerlies will maintain precip across mainly the northern half of
the forecast area through early Sunday. Warmer air pouring into
the region has produced rising snow levels since yesterday. Good
mixing is also eroding the cold air in the lower valleys, leading
to precip-type issues as snow changes over to rain or a rain/snow
mix. Suspect that most western/northern valleys will finally mix
out later today with rain the main precip-type, even in the far
northern valleys.

Rising snow levels will also confine accumulating snows to the
higher elevations of the northern mountains. Have scaled back snow
accumulations a bit the next couple days as dynamic/thermal lift
not particularly strong and the warmer temps aloft not the best
for good ice crystal growth.

By Sunday a somewhat stronger embedded shortwave will cross the
northern Great Basin. This feature will bring significantly colder
air aloft back into northern Utah to go along with the improved
dynamic lift and the rather moist air mass still in place. Looking
at the heaviest snows of this long duration event to develop
across the far north late Saturday night, then spread south during
the day Sunday. Lowering snow levels will also bring the threat
for valley snow back to the higher northern valleys during the day

Southern Utah will finally get a decent shot at rain/snow as the
colder air works south through western Utah Sunday. Not looking at
any substantial precip outside of the central mountains as the
mid-level cold air and dynamic support for lift remain well to the
north of the low-level cold air working south through the area.

A slight increase in heights across the region Sunday night/Monday
will push precip back to the north, with the best chance for a
continuation of snow confined to the far northern portion of Utah

.LONG TERM (After 00Z Tuesday)...The active pattern looks to
continue through the extended period, though the global models
continue to disagree on some of the details. After a brief break,
latest EC indicates warm advection precip developing again during
the day Tuesday while the 00Z GFS showed this starting a little
earlier. EC then moves this precipitation primarily north of the
area Wednesday into Thursday with high pressure developing, while
the GFS shifts this area of precipitation into central and southern
Utah during this time. With this divergence, have taken a broad
brush approach to POPs with limited confidence in the location of
precip over Utah and southwest Wyoming during the Wednesday/Thursday
timeframe. By day seven, all guidance indicates a broad Pacific
storm system entering the forecast area, with the potential to
produce widespread precipitation. Models have been consistent in
showing this for a few runs, so have kept POPs on the high side for
the end of the forecast period.


.AVIATION...At the SLC terminal...VFR conditions will prevail
as any lingering snow transitions to rain during the morning.
Southerly winds are expected to prevail during the daytime hours,
but nearby precipitation will occasionally cause periods of erratic
wind directions, primarily early this morning.


UT...Winter Weather Advisory until noon MST today for UTZ010.

     Winter Storm Warning until 4 PM MST Saturday for UTZ007>009.

     Winter Storm Warning until 3 PM MST this afternoon for UTZ006.

WY...Winter Weather Advisory until 3 PM MST this afternoon for WYZ021.




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