Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 182341
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
441 PM MST Sun Feb 18 2018

.SYNOPSIS...A very cold upper level trough will drop south into
the Great Basin from the Pacific Northwest late tonight. This
trough will generate a significant winter storm for much of the
area as it moves slowly east across the Greta Basin through
Tuesday.

&&

.SHORT TERM (Until 00z Thursday)...The cold core upper trough
centered across the Pacific Northwest late this afternoon will
evolve into a full latitude trough across the Great Basin for the
early portion of this week. The feature will be the most
energetic trough of what has been an anemic winter season so far
for the region.

The surface cold front associated with this trough extends west-
to-east across central Utah late this afternoon. Trailing this
surface feature is the near 700mb baroclinic boundary which has
been rather slow to move south this afternoon. Currently this
boundary is positioned just north of SLC and is the focus for a
fairly broad area of moderate/heavy snow.

This boundary should begin to move south at a faster pace this
evening as deep layer cold advection develops ahead of the upper
trough settling into the western Great Basin. Solid baroclinic
structure with this trough along with deep layer moisture and
increasing instability will result in widespread accumulating
snows along and north of the low-level boundary tonight and into
early Monday. Several inches of snow are expected with totals in
the 1-2 foot range for the northern and central mountains.

The western half of central and southern Utah will remain fairly
active Monday morning with the base of the trough sitting just off
to the west in Nevada. Northwest Utah may see a brief lull Monday
morning as a weak circulation center progged to develop over
northeast Utah creates a slight easterly component to the mean
flow across the Wasatch range. This mean layer flow will
transition back to a northwest, then west flow later Monday
through early Tuesday as the main upper trough finally moves into
and then across Utah.

Precip will taper off shortly after trough passage Tuesday
afternoon. Lingering convective showers will concentrate across
the northern mountains during the afternoon, then dissipate
quickly moving into Tuesday evening.

The bitterly cold air brought into the region by this trough will
become fully evident by Wednesday morning as clearing skies and
snow cover should allow temperatures to lower to readings not seen
this season. These cold temperatures will also keep daytime highs
below normal on Wednesday.

.LONG TERM (After 00Z Thursday)...The cold longwave trough
position will remain over the western United States in the 4-7
outlook period. That means, with high confidence, that the
temperatures will remain below normal by about 5-10 degrees.

However, confidence in the probability of precipitation remains low
through this period with the global models not only at odds in
timing and strength between each other they are also at odds within
their own ensemble members. Have gone with a blend of the Superblend
and the EC PoPs through the extended which is resulting in slightly
higher than climo PoPs which is probably a good starting point until
the models can get into some semblance of agreement.

The two most likely periods that we have a higher chance of snow
across the region, will be Thursday night through Friday and again
Saturday night through Sunday night (give or take 6-12 hrs) based on
the variability in models timing of shortwave troughs. Stay tuned as
these storms may not produce a lot of snow but because of cold
temperatures will likely have travel impacts.

&&

.AVIATION...At the SLC terminal, MVFR conditions are expected to
deteriorate to IFR by around 00Z as rain at the terminal transitions
to snow. The snow is expected to persist through the evening before
becoming more showery overnight, allowing for periods of MVFR/VFR
conditions. Northwest winds should continue through 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 UTZ001-002-007.

     Winter Weather Advisory until 5 AM MST Monday for UTZ005.

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

     Winter Storm Warning until 9 PM MST Monday for UTZ014>016-517-
     518.

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

&&

$$

SHORT TERM...CONGER
LONG TERM...STRUTHWOLF
AVIATION...TRAPHAGAN

For more information from NOAA`s National Weather Service visit...
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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