Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 241027

Area Forecast Discussion
National Weather Service Salt Lake City UT
427 AM MDT Mon Apr 24 2017

.SYNOPSIS...A series of progressively colder and energetic storm
systems will cross the region throughout the week.


.SHORT TERM (Through 00Z Friday)...In short, cool and wet weather
will be the rule across much of the forecast area through the
short term period as a series of storm systems cross the region.

Predominantly zonal flow extends across the eastern Pacific into
the interior western U.S. early this morning, and is expected to
generally remain in place through the short term period while
gradually shifting to more of a low amplitude northwesterly flow
by Thursday. Several waves embedded within this flow will bring
periods of precipitation to primarily northern Utah, but at times
extending into central and southwest Utah as well.

First up is a shortwave trough currently crossing western
Oregon/northern California. This wave is riding along the nose of
a 150kt 250mb jet which is associated with an atmospheric river
extending well upstream to the west of Hawaii. This wave is
forecast to dig a bit as it crosses the Great Basin today. The
associated cold front is forecast cross the area from west to
east, with valley rain/mountain snow breaking out late this
morning near the Idaho border, before quickly spreading south and
increasing this afternoon through this evening as the trough axis
crosses the area, and the low level flow veers to the northwest.

On the heels of this first wave, an upper low currently spinning
off the Oregon coast is forecast to dig through the Great Basin
region late tonight through Tuesday. This feature will initially
help maintain valley rain and mountain snow across the north
through Tuesday morning, but also spread precipitation across
central and southwest Utah late Tuesday morning through Tuesday

Overall maintained high PoPs across the north through Tuesday
associated with these waves, but did increase PoPs substantially
over the southwest for Tuesday.

Shortwave ridging is forecast to bring a temporary break in
precipitation Tuesday night into Wednesday morning, before the
next wave digs into the region from the northwest Wednesday
afternoon through Wednesday night, bringing another round of
precip to northern, central, and southwest Utah. With the slower
onset of this wave, have cut PoPs back considerably for Wednesday

.LONG TERM (After 00Z Friday)...Moist northwest flow remains over
the area Thursday evening. Models have come into better agreement
that the trough will dig south and begin to cut off Thursday night
into Friday, with the closed mid-level circulation directly over
Utah by 00Z Saturday. Precipitation looks to fill in nicely Friday
afternoon as the mid-level cold pool moves overhead, but low level
flow out of the due north may hinder some of the typical west-
northwesterly flow orographic precipitation. Have generally
increased POPs through this period, with the highest POPs on the
north slopes of the Uintas.

The upper low looks to push south over the Four Corners on Friday
evening, with most precip across Utah tapering off as the best
forcing and instability exits to the southeast. Details begin to
differ through the weekend, but the general idea is that the low
pushes off to the east/southeast through the day Saturday, with weak
shortwave ridging building over the area Saturday night. However,
the moist and unsettled northwesterly flow pattern looks to quickly
return Sunday and/or Monday, so continued cool/showery spring-like
weather will probably continue into May 1st.


.AVIATION...Winds at the SLC terminal are generally expected to
switch to the west-northwest between 16Z and 18Z, though increasing
shower activity through the day could make winds erratic at times.
Ceilings will lower through the day, likely dropping below 7000 feet
around 16-18Z, with a slight chance that higher ceilings persist
past 18Z if showers stay to the north. MVFR conditions are possible
in the heavier showers after 18Z.





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