Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 181759
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
1059 AM MST Sun Feb 18 2018

.SYNOPSIS...The very cold upper level trough over the Pacific
Northwest will move into the western Great Basin this evening,
then track slowly east across the region through Tuesday. The
coldest air of the season will accompany this storm, and remain
over the area through much of the upcoming week.

&&

.DISCUSSION...The very cold upper trough with a circulation center
along the Washington coast will continue southeast and developing
into a full latitude trough across the interior west for the first
half of the upcoming week. This very cold trough will move slowly
east across the Great Basin, resulting in several areas of Utah
receiving significant snowfall before precip ends late Tuesday.

The associated surface cold front appears in the mesonet data to
be just near SLC late this morning. Precipitation remains north
of this feature along and north of the near 700mb baroclinic
zone. Intensities so far have generally been light to locally
moderate with snow confined to near the Idaho border and over the
higher terrain. Expecting the intensities and areal coverage to
increase a good clip later this afternoon and evening as
convergence into the low-level baroclinic zone increases, colder
mid-level arrives with increasing dynamic and jet-level support
as the upper trough enters the western Great Basin.

By late tonight through Monday the heaviest precip, mostly as
snow, will shift into central, southern and northeast Utah as
low-level cold advection increases and dynamic support for deep
layer lift also increases as the upper trough advances through
Nevada.

One area that may see a decrease in snow would be northwest Utah.
A potential weak circulation center developing along the
baroclinic zone over northeast Utah would create some easterly
component to the low/mid-level flow, leading to a short period of
downslope flow and modest drying west of Wasatch range late
tonight through early Monday. Snow may not end entirely, but
accumulations will be reduced during that time period.

Snow will pick up again later Monday as the upper reaches western
Utah, then tracks east across the state through Monday night/early
Tuesday. This last portion of this storm will see low density
snows, so the inches of accumulation could be impressive, but
water equivalence will be on the low side.

For this afternoon and early evening rather strong southerly
winds will exists ahead of the advancing cold front. Near 700mb
winds in the 40-50 knot range with the supporting surface gradient
and decent mixing will bring strong and gusty pre-frontal surface
winds to most valleys of central and southern Utah through early
this evening. These winds will drop off gradually early in the
evening, but still remain elevated until frontal passage and the
onset of the trailing precip tonight.

The other story through midweek will be the very cold temperatures.
Both highs and lows will drop substantially from the warm weekend
readings, with these readings remaining below to well below
normals across most of the state throughout the week.

Issued an earlier update to adjust a few of the wetaher parameters
and to drop the mention of blowing snow in some of the northern
valley locations today/tonight.

&&

.AVIATION...At the SLC terminal, gusty southerly winds are expected
to shift to the northwest between 19Z and 21Z with the passage of a
strong cold front. Cigs are expected to drop to or below 6000 feet
AGL as the front approaches and conditions are expected to
deteriorate to IFR within three hours of the passage of the front
with any rain changing over to snow. The heaviest snow will fall
during the late afternoon/early evening with snow continuing into
the overnight hours.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory until 9 PM MST this evening for UTZ013>016-020-021-
     517-518.

     Winter Storm Warning until 4 PM MST Monday for UTZ006-008>010.

     Winter Storm Warning until 5 AM MST Monday for UTZ007.

     Winter Weather Advisory until 5 AM MST Monday for UTZ005.

     Winter Storm Warning until noon MST Monday for UTZ003-004.

     Winter Storm Warning until 11 PM MST this evening for UTZ001-002.

     Winter Storm Warning from 5 PM this afternoon to 9 PM MST Monday
     for UTZ014>016-517-518.

WY...Winter Storm Warning until noon MST Monday for WYZ021.

&&

$$

PUBLIC...CONGER
AVIATION...TRAPHAGAN

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http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php



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