Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 180339

Area Forecast Discussion
National Weather Service Salt Lake City UT
839 PM MST Sun Dec 17 2017

.SYNOPSIS...A ridge of high pressure will dominate early this
week. A colder storm system will arrive in Utah late Wednesday,
and impact the state through Thursday.


.DISCUSSION...A broad flat ridge is centered just off the west
coast this evening with a closed low over the central AZ/Mexico
border. The upstream ridge is nosing into the CWA north of the low
with rising heights and increasing subsidence. The fairly
extensive stratus across swrn UT has almost completely dissipated
as the drier subsiding air reached that part of the CWA.

High clouds streaming over the ridge are dissipating as they
spread south into our CWA and expect this to be more or less a
steady state condition overnight into Mon.

Some lower cloud is also spreading into the far north as H7 warm
advection begins and expect this too will persist overnight into

The warming aloft will probably not mix down very well Mon due to
the stable airmass even tho surface based inversions have not had
much of a chance to become well developed. Still, highs should
make it a little above normal.

The ridge axis moves overhead Tue then off to the east Tue night
and Wed as the next cold Pac trof digs into the PacNW states and
nrn Rockies. The latest 00z NAM continued the faster trend of the
18z run with this trof, now taking the associated cold front 2/3
of the way thru the CWA by 00z Thu, close to the 12z EC ideas.
This system still looks like it will produce accumulating snow
across much of the CWA, with mostly modest amounts if the faster
timing is correct.

Made minor update earlier to reduce sky cover srn UT tonight. No
additional updates planned.


.AVIATION...The SLC terminal will see VFR conditions through the
night. Scattered clouds near 7000 ft are expected, with a 40
percent chance of a cig at that level. Light and variable winds
are expected to become prevailing southeasterly after about





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