Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 211620

Area Forecast Discussion
National Weather Service Salt Lake City UT
1020 AM MDT Thu Sep 21 2017

.SYNOPSIS...A cold and deepening upper trough will remain over the
Great Basin throughout the weekend. The leading cold front will
sweep through the region tonight, leaving much colder temperatures
and periodic precipitation in Utah into early next week.


.DISCUSSION...The elongated trough axis extending from central
Canada southwest into California will eventually stretch apart and
produce a deep closed low across the western CONUS by Friday. This
upper low will remain over the Great Basin through the weekend,
then finally eject northeast away from the area early next week.

The associated surface cold front has settled into central Utah
with the near 700mb baroclinic lagging back across northwest Utah
this morning. Winds will be the main issue south of the surface
front with a favorable surface gradient in place and supporting
strong southwest flow aloft. Most of the current suite of wind
advisories look good at this point. The exception may be the
west-central valleys where the front has already pushed through
the area. Suspect that the front will retreat back to the north
later today as the flow aloft backs slightly with the deepening
of the trough to the west.

Organized precip will remain confined to the near 700mb baroclinic
zone across northwest Utah today. Strong low-level convergence
into this boundary supported by increasingly favorable jet support
should lead to increase in precip intensity north of the
baroclinic zone during the afternoon.

The low-level baroclinic zone will begin to rotate east through
the state tonight. Strong convergence will persist into the
boundary with increasing instability with the advance of the
trailing mid-level cold air, upper trough dynamics and a still
favorable upper level jet. Looking at fairly intense precip along
this boundary across northern/western Utah this evening. This
intense precip should weaken later tonight as the mid-level cold
air remains back near the upper trough and the gradient along the
low-level baroclinic zone weakens.

The positioning of the upper low across the Great Basin this
weekend will maintain cool temperatures and periodic showers
across Utah. Vorticity lobes rotating around the upper low will
support organized precip, with the best areas likely confined to
northeast and far northern Utah.


.AVIATION...A late fall-like front will cross the SLC Terminal later
this evening. Ahead of the main precipitation band, ceilings will
likely remain between 3500-5000 feet AGL throughout the day,
though brief improvements will be possible this afternoon. North
to northwest winds will remain through the day and into tonight.

The main precipitation band is expected to move across the terminal
between 03-08Z and may bring MVFR to occasional IFR conditions to
the terminal in heavier rain. Showers will likely to continue to
impact the terminal after 08Z.


UT...Wind Advisory until 9 PM MDT this evening for UTZ013-015-016-

     Winter Weather Advisory from 6 PM this evening to noon MDT
     Friday for UTZ007>009.




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