Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 242200

Area Forecast Discussion
National Weather Service Salt Lake City UT
400 PM MDT Sun Sep 24 2017

.SYNOPSIS...The upper low over northeast Utah late this afternoon
will track northeast into Wyoming overnight through Monday.
A new upper low will develop over western Arizona Tuesday. This
low will return north and impact much of southern and eastern
Utah during the latter half of the week.


.SHORT TERM (Through 00Z Thursday)...Cold upper level low will
continue to drift slowly NE out of Utah into west central Wyoming
by 12Z Monday. Warm advection wrap around is expected to continue
across northern Utah early this evening with favorable northwest
flow into the Wasatch Front and Mountains. Have boosted PoPs for
this evening for Salt Lake and Tooele Valleys as well as the
Wasatch Mountains.The Great Salt Lake will likely enhance the
showers this evening as well. Will keep the WSW highlights
continue until midnight, although if the 700mb flow remains more
NW linger into the evening, then the Wasatch Mountains south of
I-80 may need to be extended.

Expecting patchy fog to develop over the western valleys after the
clouds clear this evening. There was dense fog this morning in
southwest Utah and believe this will happen again. In addition,
patchy fog is likely to occur in the the mountain valleys, Cache
Valley and in southwest Wyoming late tonight into Monday morning as
precip finally ends.

Have left a chance of showers in the Uinta Mountains Monday
afternoon as another cold lobe at 500mb moves across the portion of
the CWA. Elsewhere, drying conditions are expected as temperatures
warm aloft.

Mostly clear skies across most of the CWA Monday night through
Tuesday night will allow for bigger temperatures swings. However,
max temperatures will be still 10-15 degrees below normal for time
of the season.

The EC and GFS show more energy dropping southward developing an
elongated trough Tuesday night which will close off over the Arizona
are by Wednesday. The GFS is farther south with the closing off and
has been more consistent with this feature. As it wraps up some
moisture will get brought northwest into southeast Utah by Wednesday

.LONG TERM (After 00z Thursday)...The western Arizona upper low
will be in the early stages of tracking northeast into southeast
Utah Wednesday night. The moist deep later southeast flow ahead
of the advancing low will bring some light shower activity into
the four corners region during the evening. Increasing dynamic and
thermal support with the arrival of the upper low late Wednesday
night/early Thursday will supply a fairly broad area of synoptic-
scale across south-central through eastern Utah through the day
Thursday. Temperatures aloft, though cooling a bit, will still be
sufficiently warm to keep precip as rain over all but the highest

The best lift generated by the upper low will remain primarily
over the eastern flank of this feature heading into Thursday
evening. As such, organized precip will shift into western
Colorado with lingering showers near the center of the low over
central and northeast Utah Thursday night.

The broad upper ridge across the eastern Pacific will eventually
expand into the western CONUS by the weekend. The westerlies
cresting the ridge will remain well to the north over the
northern Rockies. Embedded shortwave energy will likely
concentrate any precip along and east of the continental divide.
The only real impact may be with temps as the potential exist for
a weak back door cold front to work into northern Utah/southwest
Wyoming late in the forecast period.


.FIRE WEATHER...A cold low pressure system centered over Utah this
morning will to slowly lift northeast today. Abundant moisture
wrapping around the low will continue to bring widespread valley
rain and mountain snow to much of northern and central Utah
through this afternoon, with precipitation gradually tapering off
during the nighttime hours as the storm exits the area. Wetting
rain and areas of significant high-elevation snow accumulations
can be expected.

A drying and warming trend will follow for Monday into Wednesday.
The next storm system will develop into Arizona midweek, and as
it lifts north during the latter half of the week, moisture looks
to start spreading back into the fire district, but primarily
across southern and eastern Utah. However, temperatures will
remain on the milder side with this storm system.


.AVIATION...MVFR conditions will remain in place at the KSLC
terminal through 00-01z this evening under steady rain. Rainfall is
expected to taper off this evening allowing cigs to gradually climb,
but cloud decks are expected to remain below 6000 ft AGL through at
least 06z tonight. Erratic wind directions will be likely through
01z due to precip driven NW winds fighting a developing pressure
gradient driving south winds at this time. Will hold onto a
prevailing SE/E wind direction through 01z in TAF, but switches are
expected through the evening. Partial clearing late tonight is
expected, but only a 10% chance exists for any dense fog development.


UT...Winter Weather Advisory until midnight MDT tonight for




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