Area Forecast Discussion
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FXUS65 KSLC 282210

Area Forecast Discussion
National Weather Service Salt Lake City UT
410 PM MDT Wed Sep 28 2022

.SYNOPSIS...Moisture will continue to spread across the area
through Thursday, bringing increased precipitation chances to the
region. A cold front will move into northern Utah on Friday,
supporting continued precipitation chances before a gradual drying
trend begins this weekend.


.SHORT TERM (THROUGH 12Z FRIDAY)...An upper low is moving onto the
PacNW coast this afternoon while Utah remains under a southwesterly
flow aloft ahead of it. This flow has spread moisture into the
forecast area, and the latest PWAT analysis shows around an inch
over far southwest UT and between 0.6-0.7 inches across much of
northern and eastern Utah. Scattered showers and isolated to
scattered thunderstorms have developed across much of the area
today. While many storms were able to produce measurable rain, many
sites also reported wind gusts in excess of 40 mph as the initially
dry airmass gradually moistened through the day. However, strong and
deep convection has not been realized for the most part, given
modest SBCAPE values of 500J/kg or less. Even so, the stronger
storms and/or training of storms are still capable of producing
flash flooding in sensitive drainages, while gusty winds will remain
a possibility especially over the west deserts given over 1kJ/kg of

Expect increased shower activity developing into the west deserts
for the early evening, then spreading back into the Wasatch
Front/Mountains later tonight, while precipitation gradually tapers
off across the south. This will occur in conjunction with a weak
disturbance lifting northeast across the area. As the upstream storm
system crosses the PacNW states and approaches Utah, increased large-
scale lift ahead of the low will cause showers to focus more across
the northeast Utah/southwest Wyoming area through tomorrow, even as
PWATs decrease slightly. A cold front will then enter northwest Utah
tomorrow evening, sliding into central Utah through the night. Drier
air will spread into northern Utah behind the cold front, while
showers and a few thunderstorms continue near the boundary tomorrow

.LONG TERM (After 12Z/6AM Friday)...The extended forecast remains
mostly unchanged as an upper level trough feature is expected to
move through during the beginning of the forecast period, bringing
the minor risk for showers and thunderstorms on Friday and Saturday
with potentially some spotty precipitation lingering into the
beginning of the next work week. The trough is expected to move east
of the CWA by Monday, allowing for high pressure to take its place,
promoting subsidence, dryer conditions and a slight warming trend in
temperatures through the remainder of the extended period.

An upper level trough sitting over the NW Pacific is expected to
move onshore during the short term period and slowly build over the
region. As it develops and strengthens over the region its pressure
gradient will bring the potential for stronger winds to mix down and
create wind gusts of 25-30 knots, primarily for high terrain areas.
This wind field will also promote southerly moisture to move
northward and into the CWA which combined with proper synoptic setup
with the trough will keep the potential for showers and
thunderstorms to form Friday and Saturday and move east of I-15 and
affecting parts of eastern Utah and SW Wyoming. The trough center
will be mostly through the CWA on Sunday taking the best dynamics
for storms and showers to the north but we still see the potential
for some spotty terrain driven showers or storms on Sunday and
lingering into Monday.

Behind the trough, model guidance is building on a ridging pattern
moving in and promoting subsidence over the area. While there is the
potential for showers and storms on Monday we expect to see the
start of a loss in overall cloud coverage to begin on Sunday and
continue through the remainder of the extended which will help with
the slight up tick in the daily high temperatures while overnight
temperatures continue to fall into the 40s and 50s across the CWA.
While a majority of model ensembles move high pressure in, there is
some guidance in grids and models that would allow for some breaks
in the clear skies for some more spotty and terrain driven
precipitation by midweek.


.AVIATION...KSLC...VFR conditions and southerly winds expected for
the TAF period. Shower and thunderstorm potential will pick back up
again around 01Z and last through about 07Z. When a shower or
thunderstorm is near, gusty and erratic outflow winds will be

thunderstorms will continue to be possible throughout the CWA for
the remainder of the day. This potential will begin to taper off
after sunset and any storms that remain are expected to be primarily
in northern UT and southwest WY. Those storms should either diminish
or move out of the CWA between 09Z and 12Z. Winds will primarily be
out of the south before switching to diurnal winds overnight.
Southerly winds are expected back tomorrow. More precipitation
chances will be possible tomorrow afternoon and evening.


.FIRE WEATHER...A southerly flow ahead of an approaching storm
system has allowed moisture to spread across the area. Showers and
thunderstorms in place this afternoon are expected to continue at
times through the night, but should become increasingly confined to
the north. Many of the thunderstorms will have the capability to
produce wetting rains. As the storm system approaches northern Utah,
expect showers and thunderstorms to increase again tomorrow
afternoon, with a greater concentration across the north closer to
the storm. The airmass will dry slightly tomorrow afternoon, but
wetting rains will remain possible. A cold front will then enter
northern Utah tomorrow evening, gradually pushing into central Utah
through the night. Drier air will spread into northern Utah behind
it, while moisture will remain pooled to the south of the front.
This pooled moisture will be the focus for the bulk of the showers
and thunderstorms on Friday. As the storm system very slowly
meanders eastward, lingering showers and thunderstorms will remain
possible into the weekend, although the available moisture and
chance of wetting rain will decrease.





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