Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 221008
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
408 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.

&&

.SHORT TERM (THROUGH 12Z SATURDAY)...
Water vapor loop shows a closed low over far southern Oregon.
MDCARS wind observations show a 100kt-130kt cyclonic jet from
central California into the Pacific Northwest. GOES/HRRR/00Z KSLC
RAOB indicate the precipitable water value ranges from 0.40"-0.60"
mountains to around 1.60" in Dixie.

Majority of showers and thunderstorms will continue to coalesce
across northwest Utah today organized along the shear axis of the
cyclonic upper level jet. Another area of convection stretches
from near Kanab toward the Uinta mountains. This area forming due
to increased diffluence aloft will likely expand and become quite
heavy as the jet axis begins to near from the west this morning.

There remains a heavy rain threat due to dewpoints rising into the
60s...Precipitable water value near 1.50" and a very deep warm
cloud layer of 5-10kft. The Flash Flood Watch remains in effect.

Have issued numerous wind advisories. The one for the Great Salt
Lake Desert is for post frontal winds due to the tight thickness
gradient. Across west central and southern Utah gusty winds will
occur ahead of the cold front thanks to mixing down higher
momentum air.

Fairly strong cold advection will occur tonight which will keep
the precipitation going across the north and west as snow levels
start to near 8000ft. Snow levels may be even lower than that in
areas of higher precipitation rates. Next shift may have to raise
some headlines for high elevation impacts.

A damp and cold day is forecast for the north Friday as the cold
advection is maximized through the morning. Forecast highs are
near record low for max temperatures Friday. Snow levels look to
near 7kft during the morning.

Lake induced CAPE will likely rise to between 500J/KG and
1000J/KG as seen on modified BUFKIT forecast soundings for a GSL
temperature of 62F (Its 72F right now). Thus areas southeast of
the lake will likely see more persistent shower activity Friday
night. Elsewhere precipitation will be tapering off due to rising
heights and warming mid levels.

.LONG TERM (AFTER 12Z SATURDAY)...
Cold and moist northwest flow will remain over northern Utah
Saturday morning into early afternoon before the moisture
decreases. Have boosted pops along the Wasatch Front and Mountains
as this northwest flow will be favorable for lift as well as the
GSL should destabilize this air mass enough to produce scattered
showers south and east of it where the greatest pops have been
forecast. Have expanded the slight chance of pops into the
afternoon over the higher terrain of northern Utah as well as
south and east of the GSL. By evening the flow becomes more
anticyclonic which should turn off the precip. With clearing skies
mountain valleys and valleys of southwest Utah could see isolated
hard freeze conditions by Sunday morning.

The surface gradient tightens up across Dixie Saturday evening
through Sunday morning along with a north northeast flow at 700mb
which will combine to to create gusty canyon winds in the
neighborhood of 35-45 mph.

In the extended period from Sunday through midweek a gradual warming
trend and dry conditions will prevail. Have taken temps down just a
degree or two in many areas for Sunday through Tuesday due to low
level northerly flow remaining in place and the day-to-day increase
of 850 mb temps supports a smaller surface temp change from one
day to the next.

Have ignored the EC forecast of creating a 500mb low over New Mexico
Sunday and drifting it northwest into Utah Tuesday. The EC ensemble
no longer supports this solution so banked on the GFS as the correct
way to go.

&&

.AVIATION...
North winds at the SLC terminal are expected to shift back to
southerly between 14 and 17Z and possibly be quite gusty. However,
there is a 40 percent chance the northerly gradient will remain in
place with no wind shift until the cold frontal passage at about
22Z. There is a 20 percent chance that cigs will lower below
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 from 9 AM this morning to 11 PM MDT this evening
     for UTZ013-015-016-019>021-518.

     Wind Advisory from noon today to 11 PM MDT this evening for
     UTZ005.

WY...None.
&&

$$

SHORT TERM/FIRE WEATHER...Rogowski
LONG TERM/AVIATION...Struthwolf

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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