Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 211655
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
955 AM MST Mon Jan 21 2019

.SYNOPSIS...A potent winter storm system will continue to impact the
area today and exit by midday Tuesday. A weak weather disturbances
embedded in a moist northwest flow will impact mainly northern Utah
and southwest Wyoming late Wednesday through Thursday ahead of a
building ridge for the end of the week.

&&

.DISCUSSION...An upper trough continues to make its way across the
Great Basin this morning. This trough is associated with a 120kt jet
currently punching through southern Utah while a deepening surface
low continues to track east across southern Utah. The surface
frontal boundary is presently moving into southwest Utah and across
central Utah. Southwesterly 700mb flow of 40-50kt precedes the
midlevel boundary, with strong low/mid level convergence behind it
leading to a changeover to snow and a period of more intense
precipitation. Meanwhile, across southern Utah, the advancing vort
max has led to increasing precipitation. Rain has already started to
transition to snow across southwest Utah as that area is now under
cold air advection behind the surface low.

Expect precipitation to continue to increase across the southern half
of Utah and continue to transition to snow in all but the lowest
valleys through the duration of the morning and into the early
afternoon hours as the best dynamics continue to work their way
through that area. Across the north, snow is expected to gradually
decrease across most valleys while a northwesterly flow aloft will
maintain snowfall across orographically favored areas and
northwesterly upslope regions including some east bench locations.
However, models indicate the flow turning more northerly through the
afternoon, which would then diminish precipitation chances for many
locations north of around I-80. As a result, some winter weather
highlights could end up needing to be dropped early. The north
slopes of the Uintas and into southwest Wyoming, along with southern
portions of Utah County and the Tooele Valley should continue to see
accumulating snow under the northerly flow aloft into the nighttime
hours. The northerly flow will also maintain favorable conditions
for snow across portions of the central and southern Utah and I-15
corridor from north of Fillmore through Cedar City.

Besides the snow, postfrontal winds will increase across the area as
the surface gradient tightens, with the strongest winds expected
across favored downslope areas such as northwest Utah later this
morning and the eastern valleys this afternoon. Meanwhile, gusty
prefrontal winds will continue across southeast Utah into the
afternoon hours.

Updated the forecast to trend with latest observational and model
guidance.

&&

.AVIATION...Winter storm warning remains in effect for the SLC
terminal through this afternoon. A persistent moist NW flow will
bring prevailing IFR conditions through 18-19Z with periods of LIFR
conditions. There is a 30 percent chance that MVFR conditions will
develop by 20-21Z. Snow accumulations of 4-6 inches are expected on
untreated surfaces. NW winds will increase this afternoon causing
some blowing and drifting. Snow will gradually taper off this
evening.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory until 9 PM MST this evening for UTZ005-020-021.

     Winter Storm Warning until 9 AM MST Tuesday for UTZ007>010-517-
     518.

     Winter Storm Warning until 4 AM MST Tuesday for UTZ006.

     Winter Weather Advisory until noon MST today for UTZ005.

     Winter Storm Warning until 9 PM MST this evening for UTZ001>004.

     Wind Advisory until 9 AM MST Tuesday for UTZ013.

     Wind Advisory from 2 PM this afternoon to 11 PM MST this evening
     for UTZ011.

     High Wind Warning from 2 PM this afternoon to 5 AM MST Tuesday
     for UTZ012.

     Winter Storm Warning until 4 AM MST Tuesday for UTZ014>016.

WY...Winter Storm Warning until 4 AM MST Tuesday for WYZ021.

&&

$$

Cheng/Struthwolf

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