Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 221643
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
1043 AM MDT Thu Sep 22 2016

.SYNOPSIS...A strong cold and moist storm system will impact most
of the region through the end of the week.

&&

.DISCUSSION...Very moist airmass in place over much of the
forecast area this morning. Southern and eastern Utah is seeing
the best moisture with PWs of 1.0-1.2 inch. Elsewhere, PWs are in
the 0.8 to 1.0 range over northern Utah with an area of drier air
over west central and southwest Utah. Precipitation this morning
is primarily concentrated over two areas: in the vicinity of a
cold front stalled over northwest Utah, and in a broader area over
central and eastern Utah on the front side of the jet. Seeing
areas of flooding with persistent showers in the areas of greatest
moisture over southern and eastern Utah, where areal flood
warnings and flash flood warnings are in effect.

Instability is in place as a result of the approaching Pacific
Northwest storm system that is currently centered over western
Nevada. This system will continue east today. With daytime
heating, expecting convection to fill in across much of the
forecast area today. Dynamics are favorable for a threat of severe
weather, with gusty winds as the best threat. Increasing southerly
flow ahead of the trough will also result in some gusty winds over
southwest and west central Utah, where a wind advisory is in
effect.

The front over northwest Utah will get moving again late this
afternoon/early this evening as the main trough enters the
forecast area. Post-frontal winds over northwest Utah could get
quite gusty, so a wind advisory has also been issued for that
area. The trough will move across the forecast area through
Friday. Widespread precipitation over southern Utah is expected to
taper off overnight/Friday morning with drier air moving in, but
valley rain/mountain snow will continue throughout Friday over
northern Utah in cold pool instability. Snow levels are expected
to be near 7500 feet with potentially significant accumulations
above 8500 feet. Will need to consider winter weather highlights
for the higher elevations of northern Utah with the afternoon
forecast package.

The passage of the storm system will also bring significantly
cooler temperatures across the forecast area, particularly for
northern Utah and southwest Wyoming. Maxes Friday are progged to
be up to 30F below seasonal normals and up to 40F below high
temperatures observed yesterday. Over southern Utah, temperatures
will be more like 15F below climo, still a noticeable cooldown.
Precipitation is expected to taper off early Saturday with a drier
northerly flow moving in behind the system.

Updated the forecast earlier to make changes to sky, POPs, and
temperatures based on current trends. No additional updates
planned.

&&

.AVIATION...South winds at the SLC terminal are expected to become
gusty by 18z and will remain remain so until the cold frontal
passage around 23Z. Vicinity showers after 18z may create erratic
winds...with a 30 percent chance of thunderstorms impacting the
terminal through the afternoon. There is a 20 percent chance that
cigs will lower to BKN030 in heavier showers through 22Z increasing
to 40 percent after 22Z.

&&

.FIRE WEATHER...Yesterday`s ERC values were below the 50th percentile across
the south, while many stations across central and northern Utah
were closer to the 80th percentile.

A cold wet storm system will continue to bring periods of heavy
showers and thunderstorms to the region with most areas seeing a
good wetting rain. Winds too will be gusty across the western
valleys and southern Utah. Snow Levels are likely to fall to near
7kft by Friday.

A drying and warming trend is expected to begin this weekend
lasting into next week.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flash Flood Watch through late tonight for UTZ012-013-019>021-
     518.

     Wind Advisory until 11 PM MDT this evening for UTZ013-015-016-
     019>021-518.

     Wind Advisory until 11 PM MDT this evening for UTZ005.

WY...None.
&&

$$

PUBLIC...Traphagan
AVIATION...Verzella
FIRE WEATHER...Rogowski

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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