Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 031209
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
509 AM MST Sat Dec 3 2016

.SYNOPSIS...A cool northwesterly flow will prevail today through
early Sunday. A cold upper trough will slowly cross the area
during the first half of the upcoming week, bringing the coldest
temperatures of the season thus far.

&&

.SHORT TERM (Through 00Z Tuesday)...Early morning water vapor
imagery and objective analysis depict an upper low spinning over
the Gulf of California, with a mid level ridge in place to the
north of this feature across the southern Great Basin into
southern Utah. Meanwhile a strong pacific jet extends over the
eastern Pacific into the Pacific Northwest/British Columbia. A
subtle shortwave along the leading edge of this belt of strong
westerlies is crossing the northern Rockies currently, and
allowing a considerable amount of mid level cloud cover to spill
into northern Utah at this time. This moisture axis is expected to
slowly shift east today which may result in a decrease in valley
cloud cover, however model soundings suggest clouds remain banked
along the terrain through the day. Additionally, gusty northeast
winds across the outlying areas of Utah`s Dixie have decreased
early this morning, and as a result have dropped the wind advisory
which had been in effect.

A longwave trough is forecast to develop across much of the
central and western U.S. early next week. The lead shortwave is
forecast to dig through the northern Rockies Sunday afternoon into
Sunday night, pushing a strong but relatively shallow baroclinic
zone through northern Utah Sunday night into Monday morning. Ahead
of this boundary warm advection along the ID border late Sunday
afternoon and Sunday evening will bring a chance of snow, before
the surface boundary surges south after 06z. Given that the jet
and colder air aloft remain north of the ID border during this
time, precipitation will likely remain confined to a small
temporal window ahead of the surface boundary, as well as perhaps
a burst along the front along the terrain. Left POPs in the
valleys in the chance category Sunday night into Monday morning
given the shallow nature of the forcing. This boundary is expected
to stall across central Utah Monday afternoon with little if any
lingering precipitation along the baroclinic zone.

.LONG TERM (After 00Z Tuesday)...The low level cold front remains
draped across Utah heading into Monday night, with a break in
precipitation expected while the better mid level instability
remains upstream. As this trough slowly drops into the Great Basin
through the day Tuesday, precipitation will likely light up again
along the baroclinic zone. The big question- where will this band of
precipitation set up? Confidence is low in the placement of this
snowfall, as models have had the band everywhere from the
Utah/Wyoming border to Cedar City over the past 24-36 hours. That
said, have increased POPs to 30-50 percent across a broad area from
Ogden to Cedar City, as somewhere in that area should get a decent
shot of precipitation Tuesday. Hopefully that zone can be narrowed
as the event gets closer.

The trough continues to swing through the area Tuesday night into
Wednesday, and the precipitation pushes off to the east. Meanwhile,
the coldest airmass of the season so far is expected with this
trough, with 700mb temperatures still forecast to plunge to -20C
over northern Utah by Wednesday. Have continued to lower forecast
temperatures, particularly Wednesday and Wednesday night, with
clearing skies late Wednesday as the trough departs. The next
question, especially for Thursday morning, is how low can the
temperatures go? Suspect that even the current forecast is too warm
in some locations, and may have to lower these min temps even
further as confidence grows and forecasters manage to come to grips
with the fact that winter has arrived.

Ridging builds over the region Thursday, leading to significant low
level temperature inversions. Have trended the forecast in this
direction, including cooling down the valleys, but there still may
be too much valley warming from Wednesday to Thursday indicated in
the current forecast. These inversion conditions may not last too
long, at least in northern Utah, as models are hinting at a moist
zonal flow pattern developing Friday into the weekend, which could
potentially help to warm temperatures through mixing and/or
overnight cloud cover.

&&

.AVIATION...Ceilings below 7000 feet should develop at the SLC
terminal between 15Z and 19Z, though there is a slight chance that
ceilings remain above that level through the day. Winds will likely
turn to the northwest around 18-20Z, but no matter the direction
winds are expected to remain below 8 knots after 18Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

Seaman/Schoening

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php



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