Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 182213
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
413 PM MDT WED MAY 18 2016

.SYNOPSIS...High pressure will shift east Thursday ahead of the
next Pacific storm, which will stall over the Pacific Northwest
through the end of the week resulting in a strong southerly flow
over the Great Basin.

&&

.SHORT TERM (Through 06z Saturday)...An upper low spinning over
the Desert Southwest this afternoon will slowly make its way into
the southern Plains region Thursday, while a short ridge currently
building across the Great Basin weakens as it spreads east across
the forecast area, in response to a potent upper low forecast to
dig into the Pacific Northwest Thursday.

Lingering moisture currently in place is resulting in isolated
convection primarily along the higher terrain from the Uintas
southward through central and southern Utah. This activity should
quickly diminish with the loss of daytime heating, and have
lowered POPs for the evening hours.

As the upstream low digs into the Pacific Northwest, the
associated surface front is forecast to push into northwest Utah
Thursday afternoon. This will serve as a focus for convection
during the late afternoon and evening hours, and with a dry and
deeply mixed boundary layer dry microburst winds will be possible
across northern Utah Thursday afternoon and evening. Have
increased POPs 10-20 percent across the north Thursday afternoon
and maintained chance wording for the evening.

The upstream low is forecast to dig along the coast and into the
Great Basin Friday. This will result in strong flow spreading
across much of the forecast area through the day. 700MB flow is
forecast to exceed 50 KTS across much of western Utah during the
afternoon hours, with stronger momentum spreading across the
eastern valleys late in the day. Went ahead and issued a High Wind
Watch for most western, central and eastern valleys. Peak gusts
may approach 70 MPH across the western valleys late Friday
afternoon, while peak gusts in the Swell and Lake Powell areas
will likely remain closer to 60 MPH.

.LONG TERM (After 06Z Saturday)...Models have come in line more
with the position of the cold front near the eastern portion of
the Great Salt Lake by Saturday morning and pushing it to a
southwest Wyoming to Milford line by late afternoon. The southerly
winds should remain rather strong ahead of the this cold front
with gusts over 40 mph possible. North of the cold front winds
will be under cutting the strong southwest flow aloft making for a
much cooler day over northern Utah. The GFS shows a dearth of QPF
across northern Utah and southwest Wyoming Saturday afternoon
likely due to a marginal dry slot at mid levels. However, the
combination of good jet dynamics, 500 mb vorticity advection and
thermal advection should be sufficient enough to overcome this
somewhat deficient moisture. Therefore have increased pops to
scattered across the Wasatch Front, northern Mountains and
southwest Wyoming.

This trough gets kicked eastward Saturday night as the next
trough develops over nrn Cal Sunday. This trough will then eject
east northeast across nrn portions of the CWA Tuesday followed by
another trough pinwheeling around the overall longwave trough
anchored over northern Idaho. Therefore we keep a somewhat
unstable air mass across northern Utah through the first half of
next week while southern Utah will be on the southern fringe with
mainly dry conditions expected.


&&

.AVIATION...The SLC terminal will see VFR conditions throughout
the evening. Light northwest winds will shift to the southeast
between 03Z and 04Z ramp up late tonight with gusts over 20kts
likely by 16Z with a 20 percent chance of occurring sooner.

&&

.Fire Weather...After a couple days of scattered showers and
thunderstorms over mainly southern Utah, the emphasis will shift to
northwest Utah Thursday where some strong thunderstorms are possible
Thursday afternoon due to a strong cold front. Southerly winds are
expected to increase Thursday, especially western valleys ahead
of this cold front. The main trough will hang back over western
Nevada so this boundary will wash out over night and screaming
south winds are expected over almost the entire fire district
Friday. Although the fuels are moist strong winds in 55 mph are
likely over western valleys and over 45 mph eastern and southern
valleys. Rh values will drop into the teens through much of the
valleys each day through Saturday. Scattered showers are expected
across the northern half of the fire district Saturday through
early next week while the southern half of the district should
either be dry or have isolated showers and thunderstorms.

&&

.SLC Watches/Warnings/Advisories...
UT...High Wind Watch from Friday afternoon through Friday evening for
     UTZ003-005-013>016-020-021.

WY...None.
&&

$$

Seaman/Struthwolf

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