Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 242212
Area Forecast Discussion
National Weather Service Salt Lake City UT
412 PM MDT Mon Apr 24 2017
.SYNOPSIS...A series of progressively colder and energetic storm
systems will cross the region throughout the week.
.SHORT TERM...A rather cold, moist and unstable air mass will
prevail across northern Utah tonight through Tuesday as well as
spread into southern Utah Tuesday. Satellite imagery shows that
the jet core continues to sag southward across central Utah this
afternoon and will move into southwestern Utah late tonight into
Tuesday as ridging takes place between 130 and 140W. This ridging
will cause the shortwave entering the Pacific Northwest this
afternoon to dive southeastward into the Great Basin by Tuesday
morning. This feature will bring -26C air at 500mb across northern
and western portions of the CWA Tuesday. The 700mb temps lower to
-8C according to the GFS but only -6C to -7C by the EC. Have
split the difference and for the time do not have snow mentioned
in the Wasatch Front or I-15 corridor but its not out of the
question. The GSL could become involved for a time between 8am
and noon to create some heavy precipitation bands which most
likely would be snow. Heads up for possible such accumulations on
higher benches and across Parley`s Summit as well as in the
mountain valleys of northern Utah Tuesday morning.
With the jet diving farther south Tuesday have increased the PoPs
along the I-15 corridor and mountains of central and southern Utah
Tuesday. Temperatures will be 10-15 degrees below normal across
the CWA. As the cold pool turns the corner and moves over
south central Utah there will be an increased threat of
thunderstorms Tuesday afternoon. Isolated thunderstorms are not
out of the question farther north across the CWA.
As this system moves southeast, good subsidence should follow over
most of the area as a short wave ridge builds in temporarily
Tuesday night into early Wednesday. However this will be short
lived as the next storm system starts spreading warm advection
precip in across northern Utah mid morning Wednesday and spread
precipitation into central Utah by afternoon as the nose of the
jet penetrates into west central Utah. Good cold advection and jet
dynamics will result in widespread precipitation from about Cedar
City northward over the western valleys and mountains Wednesday
night. The GFS has -12C 700mb temps for northern Utah Thursday
morning which will easily bring snow down to the northern valley
floors while the EC is -8C which is marginal for snow. Have gone
with a rain and snow mixture for now. Winter does not want to
give up apparently.
Moderate to strong northwest flow will prevail at 700mb from late
Wednesday through Thursday which will prevent much precip, if
any, from occurring on the lee side of the mountains over
southeast and south central Utah as well as in the Uinta Basin.
.LONG TERM...Long-range models are in fairly good
agreement in the long term through the weekend. A moist, cold, and
unstable northwesterly flow aloft Thursday evening will keep
precipitation in place over mainly the northern mountains and
adjacent upslope regions before the next shortwave disturbance
carves into Utah during the day Friday. This trough is forecast to
pinch off into a closed low over eastern Utah and western Colorado
by Friday evening.
Precipitation will become more widespread on Friday with the arrival
of this next storm system. However, with more of an easterly flow
developing across northeast Utah and southwest Wyoming along the
northern periphery of the closed low Friday night into Saturday,
precipitation will become more favored across southwest Wyoming and
the north slopes of the Uintas as well as portions of western Utah,
rather than along the Wasatch Front. That being said, with 700mb
temperatures generally in the -8 to -10C range across much of
northern and central Utah, snow levels should be able to reach the
valley floors at times Friday through Saturday.
The airmass will start to trend more stable Saturday night into
Sunday as high pressure builds into the western CONUS. However, the
mean ridge position will remain to the west of the forecast area,
keeping Utah under a northwesterly flow aloft. Models suggest that
weak ripples embedded within this northwesterly flow will continue
to graze northern Utah through the early part of next week.
.AVIATION...The SLC terminal is expected to be at VFR levels into
the evening hours. Intermittent showers may briefly drop cigs to
MVFR in heavier rain. Winds may become erratic due to nearby
showers, and should remain out of the north through early evening. A
40 percent chance a southeast wind develops after 05z.
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