Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 232213
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
413 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...Surface cold front is pushing
southward across the western Utah valleys this afternoon with it
currently across Juab County angling northeast towards Spanish
Fork. The dynamics aloft are lagging behind this front by 50-75
miles and this is where the showers are developing along with
isolated thunderstorms. The northwest winds behind this front are
generally 10-20 mph with gusts to 30 mph but could gust to over 40
mph in association with any shower or thunderstorm. Although the
surface front will move across southern and eastern Utah overnight
the dynamics aloft will remain over central and northern Utah
this evening for that chance of showers and isolated
thunderstorms.

Satellite showing a crisp back edge to the cloud shield over
eastern Nevada and that clearing should reach the Wasatch Front
right about midnight. Therefore, temperatures are expected to be a
few degrees colder tonight than last night due to clearing skies
and the colder air mass moving in.

The next upstream trough will move rapidly into northern Utah
Monday morning with precip breaking out by mid to late morning
along the Wasatch Front and Mountains. Since the leading edge of
this system will be warm advection, areas favored by warm
advection; i.e. northern Wasatch Front will have the best chance
of showers prior to noon. However, by mid afternoon the trough
axis at 700 mb will pass across the Wasatch Front and the flow
will switch to northwest cold advection. Favorable jet dynamics
will also be overhead at this time. This should bring widespread
precip from about Utah County northward by afternoon. PW amounts
are only near 0.50 of an inch so not expecting widespread big rain
amounts but rather 0.20-0.50 of an inch through Monday night.
Farther south, the threat of precip will be considerably less due
to downsloping off the central and southern mountains. However,
areas along the I-15 corridor and the central mountains should see
some scattered showers.

A cold and moist northwest flow will continue Tuesday as the cold
pocket aloft moves into northern Utah keeping the threat of
showers continuing for not only northern Utah but also west
central valleys and the central mountains. The 700 mb temps will
be cold enough to support snow levels lowering briefly to the
benches of the Wasatch Front Tuesday morning.

This trough will exit and rapid drying is expected by Tuesday
evening across the entire CWA save the Uintas and southwest
Wyoming where a minimal threat will continue.

Another system will enter far northwest Utah Wednesday morning and
move southeast across most of the CWA by Wednesday evening. Below
normal temperatures and wet conditions are expected from about
Cedar City to Bryce northward Wednesday.

.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 SE wrd 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. Ptype 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 the
Pac NW will dig southeastward and close-off over the area...
resulting in cool temperatures, extensive cloud cover, and
moderate precip chances areawide. This low gradually moves
southeast of the area late Friday/early Saturday which may result
in an extended period of wraparound precipitation in areas favored
in easterly/northeasterly flow. Additionally depending on the
positioning of the sfc low a setup for easterly downslope winds
along the Northern Wasatch Front may be possible late Friday/early
Saturday. However, at this time the sfc gradient does not look
particularly favorable for this phenomenon. The low and associated
wraparound precip finally move east of the area by Sunday and
temps should warm a few degrees in most locations, although maxes
will still be running 5-10 degrees below climo across the north.


&&

.AVIATION...Conditions at the SLC terminal are expected to
remain at VFR levels through the TAF period. Northwest winds may
become gusty this afternoon with a cold front passage. Limited
precip is expected with this front, however gusty erratic winds are
possible near stronger showers. Winds are then expected to switch
back to the southeast after 03z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

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

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