Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 222157

Area Forecast Discussion
National Weather Service Salt Lake City UT
357 PM MDT Sat Apr 22 2017

.SYNOPSIS...High pressure will slide east of the area tonight
followed by a disturbance that will bring a weak cold front
across northern portions of the CWA Sunday afternoon. A series of
fast moving storm systems will cross the region this upcoming
week, initially across northern Utah then across rest of the
region after Tuesday.


.SHORT TERM (Through 00Z Wednesday)...High clouds will continue
to spread in across the region tonight as the ridge aloft slides
east of the region. A weak disturbance will move across northern
Utah Sunday afternoon with the associated cold front reaching the
central Wasatch Front around midday to early afternoon. Although
precipitation is not expected with the surface front winds will
shift to the northwest and temperatures will level off or lower
some during the afternoon from about Tooele-Utah County line
northward. The upper dynamics, albeit weak, will move in across
northern portions of the CWA late afternoon and evening. Have
expanded the chance of showers farther south into central Utah,
mainly mountains, due to the EC showing a stronger vorticity max
moving across south central Utah Sunday evening.

A temporary break in the weather will occur late Sunday night into
early Monday as a flat ridge moves overhead. However, the active
weather pattern will bring another short wave across the area with
warm advection precipitation breaking out along the Idaho-Utah
border and northern Mountains mid morning. The shortwave itself
along with the nose of the jet moves into northwest Utah late
Monday so have increased PoPs for northern Utah from about Provo
northward. The jet digs southeast across Utah Monday night which
will increase lift and also spread moisture farther south.

This jet is quite impressive as the associated moisture plume can
be seen on satellite at this time from near the Date Line
stretching back to the northern Philippines. With such a zonal
jet there are always perturbations embedded within which will be
handled differently between models. This makes timing and strength
of systems hard to pinpoint even within 72 hours. Therefore have
basically broad brushed Tuesday with above climo PoPs for the
northern two-thirds of the CWA.

.LONG TERM (After 00z Wednesday)...Longwave zonal flow draped
across the Western CONUS in the extended period sets the stage for
an unsettled period ahead.

The jet noses down from the Pacific Northwest into Nevada and Utah
bringing with it cold advection and diffluence aloft. A long fetch
of moisture remains upstream and while this setup has some
atmospheric river like features, the placement is a bit off and
forecasts the core of the moisture plume to remain off the Pacific
Coast. Plenty of available moisture will still move inland for the
interest of our forecast area however. The overall pattern through
the week remains unsettled with several waves sweeping through the
Great Basin and Intermountain West. 700mb temperatures on Wednesday
begin to decline from around -4C to -8C by Thursday under a
northwest flow pattern. The jet placement will aid in instability
and almost daily opportunities for showers and even thunderstorms
across Utah. As temperatures aloft cool rapidly and shower
possibilities remain, an opportunity for valley snow exists on
Friday into Saturday, however differences begin to come to light
as the global forecast models diverge.

The latest ECMWF run has trended towards the latest GFS, while the
previous versions of each model had done the opposite. For the week
ahead, both global models are on the same track and differ only
slightly until late Thursday, so this increases confidence a bit. By
Friday, the GFS wants to close off an upper Low nearing the four
corners area while the EC remains under a northwest flow pattern


.AVIATION...The SLC Terminal will continue to see VFR conditions
prevail through the TAF period. Winds may be light and variable at
times this afternoon before making the switch to southeast after
03z. There is a 30 percent chance winds will make the switch to




SHORT TERM...Struthwolf

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