Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 201635
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
1035 AM MDT Wed Sep 20 2017

.SYNOPSIS...A mild southwest flow will return to the area today. A
cold upper trough will move into Utah starting tonight. This
colder storm system will linger over the area through the end of
the week and into the upcoming weekend.

&&

.DISCUSSION...Mostly sunny skies are in place over Utah and
southwest Wyoming this morning, as the area is in a break between
the departing trough now over the Great Plains, and a colder
trough digging through the Pacific Northwest. This should make
today a relatively warm day across the area, with increasing
southwesterly winds in most locations.

The cold front looks to enter northern Utah this evening, then
very slowly push across the northern half of the CWA through
tonight and Thursday. Ahead of this front, southerly winds will
ramp up even more Thursday afternoon, particularly across the
southern half of Utah. Will take a close look at this wind threat
for the afternoon forecast package and consider potential wind
advisories.

Other impacts from this front will include a significant cool
down, widespread valley rain, and mountain snowfall. Will also
take a closer look at potential road impacts, and whether a snow
advisory is necessary for road snow on high elevation seasonal
roadways. The best precipitation will be late Thursday into early
Friday, with some lingering showers possible through Friday.

Updated the forecast this morning, primarily to increase sky cover
across far northern Utah for this afternoon. The previous long
term discussion follows.

.LONG TERM (After 00Z Saturday)...The EC and GFS are close in the
general pattern of the major trough over the western CONUS through
Monday but then differ on how quickly the trough departs from the
region Tuesday and Wednesday. The differences between the EC and
the GFS on Saturday is the strength of the short wave that rotates
around the base of the main trough over the Great Basin. The GFS
is broader with the main trough and does not show much energy with
the short wave while the EC is sharper with the short wave and
thus has better potential for creating lift across the CWA. Have
leaned toward the EC which keeps better consistency with previous
forecast. The GFS dries it out completely across the CWA save the
Uintas and SW Wyoming. Just seems odd that the GFS removes all
threat of precip under such a cold core at 500mb for this time of
year. Will keep scattered showers in the forecast over most of the
CWA through Sunday before finally shrinking the coverage to only
SW Wyoming and the Uintas by Monday morning.

Temperatures will remain well below normal through the weekend and
early next week despite a gradual warming trend after Sunday. The
min temperatures are expected to be very close to freezing or sub-
freezing in some western valleys Saturday, Sunday and Monday
mornings. Cloud cover will be the determinant factor as to how
cold the temperatures will get. Bottom line is that preparation
should be made now to protect gardens and orchards should sub-
freezing temperatures occur any one of those nights.

&&

.AVIATION...VFR conditions should prevail at SLC throughout the TAF
period with mid-lvl cloud cover increasing in the afternoon.
Southerly winds will prevail throughout the morning and may become
gusty after 17Z. Winds are expected to switch to the north around 22-
23Z although there is a 40 percent chance the switch to northerly
does not occur until after sunset.

&&

.FIRE WEATHER...It will be warm, dry and locally windy today, with
southwesterly winds increasing ahead of the next storm. This next
cold front will move slowly through the state late today through
late Thursday, with locally strong southwest winds ahead of the
front. Temperatures will be much cooler behind the front with
widespread wetting rain expected, along with accumulating snow in
the northern and central mountains. Cool, showery conditions could
continue into Friday and Saturday, with drier conditions heading
into next week.

&&

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

$$

PUBLIC...Schoening
LONG TERM...Struthwolf
AVIATION...Carr
FIRE WEATHER...Wilensky

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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