Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 212201

Area Forecast Discussion
National Weather Service Salt Lake City UT
401 PM MDT Sun May 21 2017

.SYNOPSIS...A weather disturbance moving southeast through Utah
will exit the state later this evening. High pressure aloft will
expand east across the western states early in the week. A warming
and drying trend will ensue through Wednesday. The next storm
system to impact the region will arrive during the latter half of
the week.


.SHORT TERM (Through 12z Wednesday)...Afternoon satellite imagery
reveals the vorticity max rotating southward through Utah on the
water vapor channel with cooling cloud tops extending to the east.
The cyclonic feature can also be seen on visible imagery, moving
eastward across Utah. Two areas of thunderstorm convection this
afternoon have been from northwest of Dugway extending southeastward
towards Scipio and from Fremont Junction eastward along I-70. These
storms seem to be brief and pulse-like, though reports of pea-size
hail have been noted. The axis of instability continues to move
south and east as the upper level trough swings through the state
this evening.

Subsidence behind the trough to the northwest is pushing into
northern Utah as a high pressure ridge is also building across the
West Coast. Northerly flow aloft settles in place going into the
early part of the week and remains through late Tuesday. Gradual
building heights with a dry air mass will allow temperatures to
climb to above seasonal normals across the area for late May.

.LONG TERM (After 12z Wednesday)...The remnant of the early week
upper ridge over the western states will exit off to the east by
late Wednesday. The exit will come in advance of another cold and
energetic Pacific storm system settling into the Pacific Northwest
and northern Rockies.

A warm and fairly well mixed air mass across the forecast area
wednesday will lead to temps hitting their highest readings of
the week, with breezy conditions developing during the afternoon.
Could see a few terrain-based showers/stroms late in the day as
patchy moisture ejects out ahead of the main storm system.

The core of this Pacific storm system will likely remain well to
the north of Utah through the extended period. The series of what
look to be energetic shortwaves will rotate around the parent
upper low, and will take aim on mainly northern Utah/southwest
Wyoming. The associated low-level baroclinic zones associated
with these feature will be the focus for convective precip, with
fairly solid dynamic lift and favorable jet support supporting
stronger convection and the potential for significant
precipitation. Temperatures aloft are not expected to be
especially cold, so accumulating snow will be confined to the
highest elevation and mainly across the northern Wasatch range.

The last in the series of shortwaves will arrive during the the
latter half of the weekend as the parent low shears off to the
east through the upper Midwest/Great Lakes. The most likely area
for precip will remain across southwest Wyoming and the northeast
quadrant of Utah along the remaining segment of the low-level
baroclinic zone. Precip will likely on the light as dynamic
support for lift will be weak, but the air mass still marginally


.AVIATION...Clouds will continue to dissipate over nrn Utah and the
SLC terminal through the reminder of this afternoon. Northwest winds
will shift to southeast about 04-5Z with a 40 percent chance of not
shifting until 06Z. VFR conditions will prevail through the TAF


.FIRE WEATHER...Clearing indices will increase across central and
southern Utah today with stronger transport winds due to a weather
disturbance bringing isolated to scattered showers and thunderstorms
to the area. Winds may be gusty and erratic at times due to the
thunderstorm activity. Clearing indices will decrease on Monday with
the light transport winds aloft, but rebound and increase Tuesday
and Wednesday area wide.

A warm and dry pattern will be in place through Wednesday under high
pressure with northwest flow aloft. A cold front is forecast to drop
down from the north on Thursday, cooling temperatures to near
seasonal normal and bringing a chance for showers and thunderstorms
to the area once again.





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