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Area Forecast Discussion
Issued by NWS Salt Lake City, UT
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FXUS65 KSLC 210349
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
949 PM MDT Wed Sep 20 2017

.SYNOPSIS...A cold upper trough will move into Utah tonight and
tomorrow. This colder storm system will linger over the area through
the end of the week and into the upcoming weekend.

&&

.DISCUSSION...An upper level trough continues to carve into the
northwestern CONUS this evening, with Utah remaining under a mild
southwesterly flow aloft upstream of this trough. A shortwave
disturbance embedded within the mean trough crossed northern Idaho
and is currently over western Montana. Although the mean trough axis
is elongated across far southern British Columbia and Alberta and
extending west of the Oregon Coast, this weak disturbance has helped
push a shallow cold front into northwest Utah. Precipitation and
thicker clouds have developed across northwest Utah behind this cold
front. Because the aforementioned weak disturbance is lifting away
from the area, the cold front will see little additional forward
progression tonight, and is even expected to weaken a bit.
Meanwhile, enhanced southwesterly winds continue ahead of the cold
front, although they will be generally weaker tonight than they were
this afternoon. Between the winds and clouds, overnight mins will
generally be a bit warmer than last night.

The trough axis will shift into the western Great Basin tomorrow as
the main vort max associated with the trough swings around its base.
This will advance the cold front through roughly the northwestern
half of Utah through the morning and afternoon hours. Stronger south
winds are expected ahead of this advancing trough and as a result,
wind advisories are in place for tomorrow. The front will strengthen
as the colder air arrives tomorrow, so precipitation should increase
along the frontal boundary. As the vort max ejects north of the area
tomorrow night, the cold front may weaken again over eastern Utah,
then strengthen once again Friday as another vort lobe swings
through. The surface front is expected to finally push through the
entire forecast area by Friday night.

With snow levels falling Thursday afternoon into Friday, expect
accumulating snow across the higher terrain especially in northern
and central Utah, generally above 6500-7000ft. The bulk of the snow
will likely fall across the northern mountains, where a winter
weather advisory is in effect.

The trough will pinch off into a closed low and linger over the area
into the early part of next week, keeping cool and unsettled weather
in place.

&&

.AVIATION...VFR conditions are expected to prevail at SLC through
at least tomorrow morning. However, CIGs will start to fall below
7000ft during the morning hours, most likely before 15z. Northwest
winds are expected to remain in place through much of tonight and
tomorrow with some occasional stronger gusts late this evening.
However, there is a 30 percent chance that southerly winds will
return after 08-10z tonight and continue through at least mid-
morning tomorrow.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory from noon to 9 PM MDT Thursday for UTZ013-015-016-
     019>021.

     Winter Weather Advisory from noon Thursday to noon MDT Friday
     for UTZ007.

     Winter Weather Advisory from 6 PM Thursday to noon MDT Friday
     for UTZ008-009.


WY...None.
&&

$$

Cheng

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