Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 222259
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
359 PM MST Wed Feb 22 2017

.SYNOPSIS...Behind the passage of an upper level trough, a cold
moist and unstable northwest flow will settle in tonight into
Friday. Unsettle conditions will continue through the end of the
week.

&&

.SHORT TERM (Through 12z Saturday)...Interesting feature early
this afternoon from IR satellite. Across northern Nevada into
southern Idaho, a circulation is making its way east while the
area ahead of this feature is creating additional lift and
diffluence with cooling cloud tops moving into northwest Utah.
This boundary will interact with our stalled cold front into this
evening bringing rain and snow to valley floors and additional
snow to the mountains. Continuing what has been and will be a very
unsettled week.

12z SLC RAOB 700mb temp registered -9C, as compared to 0C on the
previous days` 12z sounding. Quite a potent cold front that moved
into Utah yesterday afternoon. Evidence of the cold front remains
draped across central and north central Utah this afternoon with a
rather weak baroclinc zone. As the flow aloft turns northwesterly
this evening and the baroclinic zone tightens, orographics come in
to play with the terrain. The precip boundary stacks up against
the terrain along the entire Wasatch front and I-15 corridor this
evening with the cold air aloft rapidly filling in behind.
Expecting winter weather impacts across southern Utah this
evening into the early morning hours, before tapering off. Snow
levels will continue a decline to valley floors. As for central
and northern Utah, a brief break in precip is being advertised by
the models during the overnight hours. A trailing piece of energy
slides in and wrap around precip looks to redevelop closer to the
morning commute travel times. Accumulation in the valleys should
be on the modest side, with benches favoring better. With this in
mind, went with advisory products for Valley locations through the
morning commute. The mountains however, will continue to snow
through likely Friday with favorable cold unsettled northwest
flow.

The airmass continues to cool through the week. Model consensus
for 700mb temps advertise -17C through late Friday into early
Saturday. Favored areas that do well under west - northwest flow
will wring out any available moisture through late Friday before
weak zonal flow aloft transitions across the region.

.LONG TERM (After 12z Saturday)...The long term period begins
with near zonal mid-level flow over Utah as a low-amplitude
shortwave ridge flattens and moves eastward. Upstream of the Great
Basin, models are in relatively good agreement that the closed low
located just off the Oregon coast will progress southeastward and
gradually degenerate into an open wave during the day on Saturday.
The modest warm advection regime ahead of this feature may result in
some primarily orographic snow showers over Northern Utah but
currently do not expect significant precip ahead of this feature.
The decaying trough moves into the state late Sat/early Sun and
pushes a weak baroclinic zone through the state. Since most of the
limited jet dynamics associated with this system are focused in
Southern and Central Utah, currently anticipate that the best precip
coverage/intensity will be focused in this area when the baroclinic
zone arrives early Sun. This is essentially the solution portrayed
in the 12Z EC so leaned towards that model in generating PoPs for
Sunday. Also decreased PoPs slightly over northern Utah valley
locations although certainly can`t rule out some snow showers in the
moist northwesterly flow behind the front.

There is a brief region-wide lull in precip beginning Sunday
afternoon as the first wave moves east of the area, however this
break appears to be short-lived as the next pacific storm system
approaches the region Monday morning. The moist warm advection ahead
of this feature appears a bit weaker than in previous runs so
reduced PoPs a bit in areas that are not favored in southwesterly
flow such as SL and Tooele valleys. Similar to the Sat/Sun system
this wave drops a baroclinic zone through the state late Mon/early
Tues. Due to the positioning of the trough axis and upper level
dynamics, precip chances over Northern Utah will likely be a bit
higher than with the weekend system, however due to timing
differences between guidance did not significantly modify PoPs at
this time. By late Tues this wave shifts east of the area and a slow
drying trend begins. However, showery precip may linger in the
Northern Mountains through Wednesday in cold-moist northwest flow.

Max temps will generally run 5-10 degrees below climatology through
the extended and in Northern and Central Utah 700 temps will
struggle to exceed -10C during this period (except perhaps Monday
ahead of the second storm system). Thus expect snow levels to remain
below/at the valley floors outside of Dixie.

&&

.AVIATION...MVFR conditions are generally expected at the SLC
terminal through about 04Z with a 20 percent chance of temporary IFR
conditions between 01 and 04Z. There is a 30 percent chance that VFR
conditions will prevail between 05 and 11Z. Starting between 12 and
14Z IFR conditions in snow are likely and will continue until about
18Z. Winds will become northwest between about 00-01Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory until 4 AM MST Friday for UTZ007>010-517.

     Winter Weather Advisory until noon MST Thursday for UTZ001>004-
     006.

     Winter Weather Advisory until 4 AM MST Thursday for UTZ014>016-
     518.

WY...Winter Weather Advisory until noon MST Thursday for WYZ021.

&&

$$

SHORT TERM...Dewey
LONG TERM...Carr
AVIATION...Struthwolf

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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