Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 191724

Area Forecast Discussion
National Weather Service Salt Lake City UT
1024 AM MST Fri Jan 19 2018

.SYNOPSIS...A cold and moist storm system just off the west coast
this morning will track into and then through the Great Basin
this weekend. This storm will impact much of Utah and southwest
Wyoming tonight through early Sunday.


.DISCUSSION...Animation of water vapor imagery shows an elongated
trough extending from the BritCol coast south to near 32N/130W
late this morning. This trough will continue to shear apart as it
move onshore this evening, with the southern end of the trough
remain fairly well organized as it moves through Utah late
Saturday through Sunday morning.

MSAS data shows the surface trough stretch northeast-to-southwest
across far northwest Utah. The near 700mb baroclinic zone remains
immediately to north of the surface trough with weak warm
advection into southeast Idaho and increasing cold advection
across northeast Nevada.

This thermal boundary will undergo rapid frontogenesis as it moves
south out of northwest Utah this afternoon. This increasingly
strong low-level forcing supplemented by mid-level shortwaves
ejecting northeast along the boundary and the entrance region of
the jet overhead should lead to fairly strong synoptic-scale lift
over/near the low-level boundary this evening. The more intense
precip should form in the Davis/Salt Lake county area late this
afternoon, then remain on the intense side as the boundary moves
south into central Utah later this evening.

The low-level baroclinic zone will stall over central Utah, then
pivot toward a more north-to-south orientation ahead of the
advancing mid-level trough. A number of weak circulation centers
coincident to this thermal boundary along with the still favorably
positioned upper jet will maintain areas of moderate/locally heavy
snow near the boundary late tonight/early Saturday. The areal
extent and intensity of the snow will pick up and expand north and
east as the upper trough moves into the state Saturday evening.
The greatest storm accumulation will likely exist across the
southern and central mountains, with substantial number coming out
of the Uintas. For the valleys the greatest totals at this point
look to be focused on the west-central and southwest valleys,
particularly along the I-15 and western I-70 corridors.

Lingering snow showers associated with the mid-level cold pool
will persist into early Sunday, then rapidly dissipate as the air
mass aloft drys and warms Sunday afternoon/evening.

The current suite of warnings and advisories look good at this
point and time. No updates planned.


.AVIATION...Winds at the SLC terminal will likely switch to the west-
northwest around 19-22Z, then increase in speed/gustiness after 00Z
when the true cold front moves through. Rain or rain/snow mix
showers are possible 21-01Z, with ceilings dropping below 7000ft in
that time frame, followed by likely IFR/LIFR conditions in snow
starting 01-03Z. Snow accumulation on untreated surfaces is expected
to be 1-3 inches through 12Z Saturday, with the potential that snow
showers continue past that time.


UT...Winter Storm Warning from 6 PM this evening to 5 AM MST Sunday
     for UTZ008>010.

     Winter Weather Advisory until 9 AM MST Saturday for UTZ007.

     Winter Storm Warning from 5 PM this afternoon to 11 PM MST
     Saturday for UTZ003-004-006.

     Winter Weather Advisory from 4 PM this afternoon to 9 AM MST
     Saturday for UTZ002-005.

     Winter Storm Warning from 11 PM this evening to 5 AM MST Sunday
     for UTZ517-518.

     Winter Storm Warning from 9 PM this evening to 5 AM MST Sunday
     for UTZ015-016.

     Winter Weather Advisory from 9 PM this evening to 5 AM MST
     Sunday for UTZ014.

WY...Winter Storm Warning from 6 PM this evening to 5 AM MST Sunday
     for WYZ021.




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