Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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277
FXUS65 KSLC 201019
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
419 AM MDT Fri Oct 20 2017

.SYNOPSIS...A storm system will sweep east across the Great Basin
through this evening. An associated strong cold front will bring
substantially colder temperatures to Utah through Saturday. High
pressure will return for the first half of next week.

&&

.SHORT TERM (THROUGH 12Z MONDAY)...Southwesterly flow aloft will
continue to increase across the forecast area this morning ahead of
an upstream trough. The surface cold front associated with this
trough is currently over western Nevada, per MSLP analysis. This
front is expected to arrive over northwest Utah around mid-morning,
then surge southeast through the afternoon hours and exit the area
during the evening. Winds will be gusty both ahead of and behind the
front, and a few sites may briefly reach advisory speeds, but
widespread strong winds are not expected due in part to the timing
of the front.

Precipitation is expected to develop near and behind the cold front.
Most of it will be tied to the frontal band, and due to the fast-
moving nature of the front, precipitation is expected to be short-
lived. As a result, precipitation is not expected to be significant,
and will occur mainly over northern and portions of central Utah.
Snow levels are expected to fall to around 5500 feet before
precipitation largely tapers off this evening.

A much cooler northwest flow will remain in place into tomorrow.
Clouds will increase across northern Utah tomorrow afternoon as
700mb warm advection begins. These clouds and warming aloft will
trap cool air in place across the valleys. Any precipitation
associated with the warm advection looks to be light and confined to
near the Idaho border.

High pressure will settle in across the western CONUS on Sunday,
brining dry and stable conditions. Temperatures will trend warmer,
but low-lying areas will have a more difficult time warming up as
inversions set up.

.LONG TERM (After 12z Monday)...A fairly benign pattern will set up
across Utah for much of the long term portion of the forecast. Upper
level ridging will continue to build into the area through at least
Tuesday. Given that it is late October and a significant amount of
mid-level warming is expected, valley inversions will likely
strengthen through Wednesday, though this will result in more of a
reduction in temperature and some hazy skies rather than a January
like fog/thick haze.

A splitting upper level trough will approach the Pacific Coast
Wednesday...and progress to the Interior West by Thursday. 00Z model
runs have trended deeper with this system as it crosses Utah, with a
stronger shortwave, jet support and forcing for precipitation.
Started increasing pops for the Thursday afternoon/evening period
for the mountains of northern Utah. If run to run consistency
continues to show a stronger southern split, pops will likely need
to increase further. Regardless, ridging builds back into the
Interior West behind this system by Friday and remains in place into
the weekend.

For the most part, temperatures will remain near to slightly above
normal through the long term portion of the forecast.

&&

.AVIATION...Gusty southerly winds will continue to develop at the
SLC Terminal through early morning. A cold front will approach this
morning. This will produce a wind shift to the west to northwest
between 16-18Z. As the wind shifts, expect west to northwest winds
to remain gusty through at least 00-01Z.

&&

.FIRE WEATHER...Southwest winds will continue to strengthen this
morning as a storm system approaches the area. This storm will push
a cold front through the state, beginning mid-morning across far
northwest Utah and progressing southeast through this evening before
exiting the area. Much cooler temperatures and higher humidities
will spread into the area behind this front through tomorrow.

Valley rain and mountain snow is expected along and just behind the
cold front, but is not expected to be long-lived and will be
confined mainly to northern and portions of central Utah.
Precipitation amounts will not be large, and chance of wetting rain
will be slim across much of central and southern Utah.

High pressure will build back into the area through the middle of
next week, bringing warmer temperatures and a gradual drying trend
under a stable airmass. The next storm system could possibly impact
the area during the Wednesday night through Thursday timeframe.

&&

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

$$

Cheng/Kruse

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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