Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 182156
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
356 PM MDT Tue Jul 18 2017

.SYNOPSIS...Monsoon moisture will spread across the Eastern Great
Basin Wednesday and Thursday, increasing shower and thunderstorm
activity and bringing the potential for heavy rain.

&&

.SHORT TERM (Through 12z Friday)...Water vapor imagery showing
moisture is moving northward along the Nevada/Utah border as far
north as Juab Co. Although the GFS is the outlier with a forecast of
showers reaching the GSL by midnight there are some reasons to
believe that it may not be too far off due to the development of
cumulus over east Central Nevada and over the mountains of southern
Tooele County. The PW forecast of nearly an inch over the southern
portion of the Great Salt Lake Desert is also hard to ignore.
Therefore have added PoPs as far north as SLC for this evening.
farther south where the moisture is deeper there will again be at
least isolated heavy rain producing thunderstorm through this
evening.

A disturbance over the Arizona/New Mexico border is forecast to move
west northwest tonight which will be on the doorstep of southern
Utah by Wednesday morning. Deep moisture will move north with this
system with 1.4 or better PW moving into Dixie. This deep moisture
is expected to move as far north as central Utah by Wednesday
afternoon/evening. Have issued a Flash Flood Watch for this across
the southern half of the CWA. Have lowered temperatures across
southern Utah as cloud cover and rain should prevent temperatures
from reaching their potential.

Across northwest Utah, the leading edge of these storms will likely
be dry with gusty winds so have gone ahead with a Red Flag Warning
there.

Moisture will remain in place over most of the area Thursday with
another day of possible heavy rain over portions of the southern and
central Utah. Northwest utah should remain on the northern edge of
the deeper moisture so scattered showers and thunderstorms are more
likely

.LONG TERM (After 12Z Friday)...Weak mid level disturbance will
glide across the Northern Rockies on Friday, flattening the ridge,
and facilitating a somewhat dry west to northwest flow across the
northwest third of the forecast area, though more so in the NAM
than GFS and ECMWF. A chance for showers and thunderstorms will
continue across the remainder of the forecast area into the
evening hours.

With a drier air mass in general across the forecast area on
Saturday and Sunday, coverage and intensity of shower and
thunderstorm activity will decrease, though will still need to
hang on to slight chance to chance wording for showers and
thunderstorms over southeast half of forecast area, though
somewhat focused over higher terrain.

Models suggest ridge of high pressure will center over Four
Corners area Monday afternoon and evening, with a moist south to
southwest flow once again returning to the region. Coupled with
some upper level support as jet max and associated mid level
disturbance slide across northern portion of the great basin from
late Monday into Tuesday period, expect better coverage of
showers and thunderstorms.

&&

.AVIATION...Winds at the SLC terminal are expected to prevail from
the northwest this afternoon with periods of variable direction and
erratic gusts from passing isolated thunderstorms through about
01Z. VFR conditions will persist through the day under mostly
clear skies with episodic scattered cigs at 12kft AGL.

&&

.FIRE WEATHER...A weak disturbance will move northward from
Arizona and reach southern Utah by Wednesday morning. Deep
moisture will accompany this disturbance and spread the moisture
northward through the day. The northern edge of this moisture may
produce isolated dry thunderstorms and strong outflow winds so
have issued an RFW for FWX zone 478. Wetting rains are likely in
many areas of southern and central Utah Wednesday into Thursday.
Flash flooding is possible over the Brian Head burn scar.

Drier air will spread into NW Utah Friday and into central Utah
by this weekend with the exception of the higher terrain where
showers and thunderstorms will linger. Temperatures will remain
above normal but will be closer to about 5 degrees above normal
rather than the 5 to 10 degrees of recent days.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flash Flood Watch from Wednesday morning through Wednesday
     evening for UTZ010-012>016-019>021-517-518.

 Red Flag Warning from 11 AM to 10 PM MDT Wednesday for UTZ478.
WY...None.

&&

$$

SHORT TERM...Struthwolf
LONG TERM...Barjenbruch
AVIATION...Verzella
FIRE WEATHER...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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