Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 201154

Area Forecast Discussion
National Weather Service Salt Lake City UT
454 AM MST Fri Jan 20 2017

.SYNOPSIS...The active weather pattern will continue across the
region, with a series of weather systems crossing the area through
the first half of next week.


.SHORT TERM (Through 12z Sunday)...The forecast area remains in
between two shortwave features this morning, one wave moving away
from the region through the central/southern Rockies, and an
upstream wave currently making landfall along the California
coast. With ample boundary layer moisture in place, a fairly
expansive area of low stratus and fog encompasses most valleys
across the forecast area. This fog became quite dense across
portions of the Wasatch Front, and have continued the going Dense
Fog Advisory through mid morning, while based on web cams and
surface observations it appears the fog across the remaining
valleys is a bit more patchy, and thus have left these area out of
the advisory. Would anticipate most of this fog to burn off or
lift into a low stratus by late morning, although it`s possible
areas of fog do hold on into the afternoon hours.

The upstream wave is forecast to dig through the lower Colorado
River Valley and into the Desert Southwest tonight through the day
Saturday. Strong moisture advection will overspread far southwest
Utah this afternoon, with the attendant mid level trough axis
crossing the forecast area tonight into the morning hours
Saturday. As such precipitation will spread into far southwest
Utah this afternoon, then increase across the remainder of the
area overnight. As the trough axis passes, snow will likely
continue along the I-15 corridor into the morning Saturday before
diminishing. Snow levels through the event will remain near
4000-4500 feet before lowering Saturday morning behind the trough.
Could see a period of moderate rain this evening across Washington
County which may lead to rises on area rivers and streams.
Otherwise modest valley accumulations are generally expected, but
may need a winter wx advisory if models remain consistent. Mid
level ridging will briefly follow late Saturday through Saturday

.LONG TERM (After 12Z Sunday)...As has been the case the last few
model runs, global models continue to indicate a lull in the action
Sunday morning. The next system will begin to impact the area Sunday
afternoon as a strong 160kt+ jet max takes aim on Utah. Upper level
diffluence combined with deep southwesterly flow and associated warm
air advection will provide more than sufficient lift for
precipitation across portions of Utah. The main locations to see the
highest precipitation rates will be portions of southern Utah
experiencing enhanced upslope flow and mountain areas of Utah
favored in southwesterly flow.  Locations such as Cedar City and the
Salt Lake Valley will likely be shadowed until the cold front

The cold front associated with the digging trough is expected to
cross the state Monday into early Tuesday. Expect an enhanced area
of precipitation near and behind this cold front.  A large and
somewhat diffuse trough will remain across the West through at least
Thursday. This will keep deep, moist and unstable north to
northwesterly flow in place. Expect at least mountain areas to
continue to see snow showers from Tuesday through Thursday.

Upper level ridging will finally build into the area by Friday
bringing a break to the action through at least the early part of
the weekend.


.AVIATION...Dense fog continues at the SLC terminal this morning.
RVRs have remained below about 1600 feet through the night with
ceilings near 200 feet. Expect dense fog to remain in place through
at least 16Z, with a gradual dissipation in the reduced visbys to
near 3-5SM by 18z. One of the main questions is whether the stratus
deck will lift or remain in place. Currently expect the stratus to
dissipate this morning but there is a 40 percent chance stratus
hangs on through the day with IFR or LIFR bases.


UT...Dense Fog Advisory until 10 AM MST this morning for UTZ002-003.




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