Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 192217

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

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


.SHORT TERM (through 12Z THURSDAY)...Closed low off the So Cal
coast assisting in bringing sub tropical moisture northward across
Arizona in the form of high clouds today and these clouds will move
into southern Utah overnight. The EC still farther west and faster
with bringing low level moisture into southern Utah Tuesday morning
while the GFS aims the main moisture towards Kane County and Lake
Powell region and not until afternoon. Since each have their own
merit ended up blending their solutions for the forecast. Therefore,
have backed off on the timing and the probability of precip across
southern  and central Utah Tuesday.

Farther north, another warm day is in store for Tuesday under sunny
skies early along with southerly breezes but an increase in clouds
should aid in preventing SLC from reaching the record for the day of
91 degrees.

The first surge of sub tropical moisture moves east of the area late
Tuesday night/early Wednesday but will fill back in somewhat later
Wednesday afternoon as the strong upper level trough approaches. Not
so bold on POPs Wednesday afternoon as 500 mb temperatures still not
cooling and jet dynamics still over Idaho and Nevada so backed off
to mainly slight chance CWA wide. The cold trough moves closer
Wednesday night with the jet dynamics moving over northwest Utah by
12Z Thursday and deep moisture moving into southwest Utah.
Consequently, have likely POPs over most northern portions of the
CWA and chance elsewhere.

.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

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...Operational weather concerns will remain minimal at the
KSLC terminal through the valid TAF period. Northwest winds are
expected to develop during the 22-23z timeframe, with a 20 percent
chance winds remain south through the duration of the afternoon.
VFR conditions will prevail.


.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.




LONG TERM...Schoening

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