Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 200351

Area Forecast Discussion
National Weather Service Salt Lake City UT
951 PM MDT Mon Sep 19 2016

.SYNOPSIS...Dry and stable conditions will continue overnight.
A weather disturbance moving northeast through the Great Basin
will draw moisture into far southern and eastern Utah Tuesday and
Tuesday night. A much stronger storm system will impact most of
the region late in the week.


.SHORT TERM (Until 12z Thursday)...The moisture working north
ahead of the upper low currently positioned near 22/123 has
reached central Utah at mid-evening. The moisture over Utah
remains at the high levels and will offer no chance at precip
overnight. The last usable GOES PWAT imagery put the .60 inches
PWAT values on the Utah/Arizona border, which matches up well the
GFS guidance from the 18z model run.

A number of weak dynamic feature, including a decaying tropical
system, will follow the moisture north into southern/eastern Utah
Tuesday morning through late Tuesday night. These features will
shear off to the east-northeast as the move into the southern
Great Basin. As such the mainly impacts in terms of precip will
be confined to extreme southern/eastern Utah. Based on the nature
of the air mass will look at warm rain processes to dominate, with
the potential for locally heavy rains late Tuesday/Tuesday

Backing flow aloft ahead of the deep/cold upper trough digging
into the west coast states will draw moisture north across much of
the state Wednesday. This moisture will be likely spawn additional
shower/thunderstorms activity further north and west Wednesday
afternoon/evening. The main trough will likely be too far removed
to the west to offer much in the way of dynamic support for
significant convection. Will watch for shortwaves ejecting out
ahead of the main trough, with extreme northwest Utah the only
real area open to enhanced convection Wednesday night.

.PREVIOUS LONG TERM (After 12Z Thursday)...The large upper trough
pushes into the Great Basin in earnest through the day Thursday,
with widespread rain expected across Utah and southwest Wyoming.
Over the past couple of days, models have been trending further
south with some of the better mid-level forcing, so have increased
POPs and sky cover for southern Utah, to go along with the
already-high POPs/sky across the north. With 700mb temps in the
2-8 degrees Celsius range, precip through the daytime hours should
fall as rain at practically all elevations, except maybe the
highest of peaks.

Colder air will move into the area Thursday night into Friday, as
the closed low moves across the region, with snow levels forecast
to drop to around 7,000 feet. Wrap-around precipitation is
expected to continue the wet weather for the northern half of the
CWA Thursday night through Friday night, with a chance that this
precip could linger into the daytime Saturday. The cold air and
precip will likely combine to make Friday the coldest day since
May in many locations.

The low center pushes east of the CWA on Saturday, but the recent
model trend has been to keep a significant portion of the low near
the Four Corners Saturday night, and then potentially impacting
southern Utah again on Sunday/Monday. Confidence in this portion
of the forecast remains quite low until the models come into
better consensus about how to handle this remnant feature.


.AVIATION...A stable and still quite dry west-southwest will
remain over the terminal area through the TAF period. Southeast
winds will persist overnight, then a more southerly and increase
by late Tuesday morning.


.FIRE WEATHER...Sub tropical moisture moves in across southern Utah
Tuesday but it should generate less than 0.25 of an inch through
Tuesday night and since this a warm stable system the threat of
lightning is minimal at best. The main threat will be gusty winds
southerly winds expanding northward from the precipitation across
central and northern Utah during the afternoon. This moisture exits
Wednesday morning but more moisture associated with Hurricane Paine
will begin to move into the area Wednesday afternoon. Since the
dynamics from the incoming cold trough are still over Nevada felt
that the chance of showers was only minimal so backed off on the

The cold trough moves in late Wednesday night through Thursday night
with widespread wetting rains over most of the area especially
northern Utah where the dynamics will be the strongest. Snow levels
will lower Thursday night with accumulating snow above 7k ft across
the central and northern mountains. Precip amounts of 1-2 inches are
possible over northern Utah with 0.30 to 1 inch over southern areas
through Friday. Temperatures will be at least 30-40 degrees colder
Friday than Tuesday.





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