Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 111201
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
601 AM MDT Fri Aug 11 2017

.SYNOPSIS...Moisture will continue to spread north across
southern Utah and into central Utah through Saturday. A drier
airmass is forecast for much of next week.

&&

.SHORT TERM (Through 12Z Monday)...A shortwave ridge remains in
place over Utah this morning with the upper jet over central Utah
starting to shift east out of the area. The upper low that had
resided over northern California the last several days is finally
starting to lift northeast into Oregon. However, subtle weak
disturbances have continued to eject out of this low. One such
disturbance is currently exiting Utah into southwest Wyoming, while
another weak impulse should be making its way across Nevada through
the afternoon hours.

A thin line of showers and thunderstorms extending from the salt
flats to the Uintas developed overnight and persisted for the past
several hours. These storm may have been due in part to the wave
currently exiting the area but perhaps more due to weak low-level
convergence and some jet dynamics. However, these storms look to be
weakening this morning. Otherwise, much of northern Utah with the
exception of the Uintas can expect to see generally isolated
convection today as PWATs are trending downward. The aforementioned
disturbance over Nevada is forecast to clip northwest Utah late this
afternoon into this evening. This area could see a bit of an
increase in showers later today as a result.

Focus will be shifting more towards southern Utah as moisture there
has been trending upward. Mesoanalysis and GOES sounder both
indicate PWATs have reached an inch along the Arizona border. A
cluster of showers and thunderstorms developed across southwest Utah
overnight which produced heavy rain based on radar estimates,
although most of this heavy rain missed the precip gauges. These
storms developed along the moisture gradient and near the right
entrance region of the upper jet and where a tongue of instability
extending from Arizona and Nevada exists, per mesoanalysis. Although
these storms have weakened, expect an increase in activity again
later today. The moisture will then spread into central Utah tonight
into tomorrow leading to greater areal coverage of thunderstorms.

While shower activity is expected to remain fairly isolated across
northern Utah tomorrow, models are suggesting a shortwave
disturbance will rotate into at least the southern and central
Wasatch Front tomorrow night. This could bring some nocturnal
showers to the area as a result. Otherwise, PWATS look to start
trending downward on Sunday as the ridge begins to flatten and the
flow turns more westerly in response to a trough pushing into the
Pacific Northwest. However, expect that lingering low-level moisture
and instability will remain sufficient to allow isolated to
scattered showers and thunderstorms to continue across all but far
northwest Utah on Sunday.

.LONG TERM (After 12Z Monday)...Medium range models in good
agreement through the middle of next week before diverging a bit
late in the period. Upper level ridge axis is expected to shift east
over the central plains as a baggy trough settles into the western
U.S. Models agree that residual moisture will linger across much of
Utah early in the week. With sufficient lapse rates and instability
still in place anticipate isolated to scattered convection on Monday
afternoon and evening. It may also be a bit breezy across western
portions of the state as southwest flow aloft increases.

Models begin to dry the area out on Tuesday and ECMWF and GFS and
ensembles indicate that by that time convection will be more
confined to the eastern half of the state. After this time much
drier air overspreads the region limiting convective potential
through the rest of the week.

Temperatures are expected to be near normal across the area through
much of next week.

&&

.AVIATION...VFR conditions will prevail through the TAF period. A
few showers will be in the vicinity of KSLC through 13Z and these
showers may produce brief gusty and erratic winds. There is also a
10 percent chance that a thunderstorm could occur in the vicinity of
the terminal during this time. Winds are expected to become
northwest between 17Z and 19Z although there is a 20 percent chance
that they could switch before this time.

&&

.FIRE WEATHER...Moisture will continue to increase into the southern
half of the fire district today. This will bring increased chances
for showers and thunderstorms across southern and portions of
central Utah today through the weekend. The stronger storms will be
capable of producing wetting rain, which may be locally heavy at
times. Gusty winds will be possible with some storms as well.

Across northern Utah, a drying trend will result in fewer showers,
although a weak weather disturbance expected Saturday night into
Sunday could bring a brief increase in convection. Otherwise, storms
across the north will generally not be as wet as the last few days
but will produce gusty outflow winds. A drier airmass is then
expected to spread into entire area beginning midweek.

&&

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

$$

Cheng/Graham

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For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php



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