Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 131704

Area Forecast Discussion
National Weather Service Salt Lake City UT
1004 AM MST Tue Feb 13 2018

.SYNOPSIS...The upper level low pressure system over California
will drift offshore today. The next trough will move in from the
Pacific Northwest Wednesday night through Thursday.


.DISCUSSION...A closed low is over California and southern Nevada
this morning, and will continue to weaken and slide offshore over
the Pacific through the next 24 hours. On the eastern edge of this
low, precipitation is continuing across the southern half of Utah
this morning, with coverage of showers expected to decrease
through the day.

Accumulating snowfall was observed as low as about 4000 feet in
southern Utah this morning, with snow observed on some roadways,
especially in the higher terrain. Winter weather advisories remain
in effect, both for the central/southern mountains and a couple
of valley zones across the south. Based on radar/satellite and web
camera trends, will likely allow these headlines to expire as
planned through the day.

After a break between storm systems tonight through early
Wednesday, another trough is forecast to drop into the Great Basin
from the north Wednesday afternoon through night. While this is
not expected to be particularly strong storm, one question mark is
how much moisture this trough will tap into from the south. If
that connection is made, parts of southern Utah could get some
decent precipitation values, as currently seen in the 00Z run of
the ECMWF.

The forecast for today looks good, and no updates are anticipated
other than the planned expiration of the winter weather
advisories. The previous long term discussion follows.

.LONG TERM (After 12Z Friday)...As the shortwave trough slides to
the southeast by early Friday, warm advection northwest flow filters
in across northern Utah. Both extended models hint at a weak brush-
by shortwave late Friday that will just clip northeastern Utah and
move into southern Wyoming and northern Colorado. This should
increase cloud cover a bit, but keep most precipitation well to the
north of our forecast area.

Going into the weekend the models begin to really diverge from one
another, surprise surprise. However, both the GFS and the ECMWF
remain consistent run to run with the respective model runs, so
there`s that going for them. In past experience over the last week
or so, the EC seems to have been more consistently unchanged while
the GFS tends to flip flop more, so I leaned more towards the EC.

A digging trough slides south through the Great Basin Saturday into
Sunday from the EC, while the GFS opens a broad longwave trough
draped across the northern Rockies. The EC has a better advertised
baroclinic zone with more frontogenetic forcing Sunday, with 700mb
temps dropping to -14C with better available moisture. While the GFS
finally digs a trough into the Great Basin by Tuesday, the EC
further enhances the trough with a cut off low forming overhead of
Utah by late Monday. Differences aside, this pattern looks very
active and through the weekend a storm system looks promising to
bring some much anticipated winter precipitation to at least a good
portion of Utah.


.AVIATION...Light winds at the SLC terminal will remain
predominantly north through the day. Winds will shift to the
southeast between 03-04z this evening. Scattered cigs at or above
7000 feet should remain to the south and east, confined to the
higher terrain through early afternoon.


UT...Winter Weather Advisory until noon MST today for UTZ013-020.

     Winter Weather Advisory until 4 PM MST this afternoon for UTZ517-




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