Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 240412

Area Forecast Discussion
National Weather Service Salt Lake City UT
1012 PM MDT Sun Apr 23 2017

.SYNOPSIS...A series of progressively colder and energetic storm
systems will cross the region beginning today, and continuing
through the upcoming work week.


.SHORT TERM (Through 00Z Thursday...The first in what will be a
series of progressively colder weather disturbances is moving
through Utah this evening. This feature was supported by decent
low-level cold advection, but only weak dynamic and thermal
support at the mid and upper level. Light convective precip was
the extent of any precip, with this likely to exit the state by
around midnight.

Winds were a much greater issue with the front today. Gusty south
winds developed as expected across west-central through southern
Utah in the pre-frontal environment. Rather strong pressure rises
behind the front early this evening resulting a short period of
very strong post-frontal west winds, mainly concentrated through
west-central Utah eastward along the I-70 corridor. Winds will
remain gusty out of the west-northwest for a few more hours as the
the surface gradient gradually relaxes across central and eastern

A persistent cyclonic westerly flow will usher in a couple more
fast-moving shortwaves on Monday. These subsequent features will
show a little better baroclinic structure and moisture as they
focus on northern Utah and southwest Wyoming. Precip may be more
persistent across the mountain mountains and adjacent windward
valleys as fairly deep and moist cold advection will exist through
Monday evening.

By late Monday night/Tuesday the pattern will see some
amplification of a shortwave ridge off the west coast, which will
forcing the next system out of the Pacific Northwest southeast
into the Great Basin. This feature will bring a tight cold pool
aloft to work with as it tracks through the region Tuesday.
Convection associated with this feature will likely develop
quickly as the air mass should experience rapid destabilization
with the arrival of the shortwave and the associated mid-level
cold pool. Favorable jet support will also contribute to what
could turn into deep convection Tuesday afternoon/early evening.

Shortwave ridging Late Tuesday night/Wednesday morning will create
a short break in organized precip. Following the passing
shortwave ridge a strong, moist and somewhat cyclonic west-
northwest will set up across the region. Precip will likely
increase again Wednesday afternoon, though the bulk of the heavier
precip will likely exist beyond the short term period.

.LONG TERM (After 00Z Thursday)... The long term period begins with
some notable discrepancies evident between the GFS/CMC and EC
solutions. All guidance depicts a shortwave trough diving into
Northern UT coincident with a NW-SE oriented upper level jet more or
less bisecting Utah. The GFS/CMC are more amplified with the
shortwave and also position the jet in a more favorable location
over NW UT and these dynamical features provide the ingredients for
frontogenesis in that area early Thurs. The tightening baroclinic
zone then pushes southeast through Northern/Central portions of
the area Thurs AM resulting in a large swath of fairly intense
frontal precip impacting Northern/Central Utah. 700 temps then
cool considerably in the wake of the front decreasing to near -10C
by late Thurs/early Fri, consequently any precip falling in this
time would fall as snow in most locations. The EC is less bullish
with the Thurs shortwave, resulting in less forcing for
frontogenesis, additionally mid-level flow is more zonal limiting
mid-level cold advection. However, even if the EC solution
verifies moisture and large-scale ascent from jet
dynamics/shortwave should still be sufficient to produce some
valley rain/mountain snow early Thurs in the north, thus decided
to raised PoPs on Thurs over the North. The EC does finally get
the front going Thurs PM over Central Utah resulting in a period
of relatively heavy precip over the Central Mountains.

Showery precip will likely continue in Northern/Central Utah on
Friday in the cool moist NW flow, with some lake enhancement
possible as well, contingent on low-level moisture and thermal
profiles. Precip-type will be an issue during this period as the
CMC/GFS solutions would drop snow levels to valley floors while
the EC solution would keep snow levels around 5.5-6K feet. Hedged
a bit keeping most of the valley precip as rain but switching to a
mix after 12Z Friday... future shifts may have to modify this if
the EC trends towards the North American models. Guidance is in
good agreement that during the day Friday a mid-level trough over


.AVIATION...Dry/stable conditions behind today`s cold front will
maintain VFR conditions at the terminal through Monday morning.
Light southeast drainage winds will gradually turn more southerly
and show a slight increase for later tonight through Monday
morning. The next weather disturbance will arrive at the terminal
between 17z and 19z.





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