Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 190424

Area Forecast Discussion
National Weather Service Salt Lake City UT
1024 PM MDT Tue Jul 18 2017

.SYNOPSIS...Monsoon moisture will spread into the forecast area
tomorrow, increasing shower and thunderstorm activity and
bringing the potential for heavy rain and flash flooding tomorrow
and Thursday.


.Discussion...This was an active afternoon and evening for parts
of the Desert Southwest, with strong thunderstorms across
portions of Arizona and Nevada. The SPC mesoanalysis page
indicated a favorable convective environment in terms of moisture
and instability extending into southern Utah this afternoon.
However, the upper-levels were not as favorable with much less
steering flow and more subsidence over our area. Thus,
thunderstorm coverage was more limited for southern Utah and more
pulse-y in nature, while drier conditions over northern Utah and
southwest Wyoming suppressed most convective activity. One
training cell did prompt a flash flood warning for the Brianhead
Fire burn scar, and another strong cell in Iron County displayed a
notable three-body scatter spike and thus prompted a severe
thunderstorm warning for hail.

Convection has waned as of this writing, though remaining activity
is still electrically active. Latest high-res guidance suggests
only isolated coverage of showers and thunderstorms overnight.

Previous forecast is in good shape, so no updates planned this
evening. Main focus continues to be flash flood potential tomorrow
and again Thursday.

Previous discussion, issued 356 PM...

.SHORT TERM (Through 12z Friday)...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

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

.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...Light southeasterly winds at the SLC terminal tonight
will likely switch to the northwest around 20Z tomorrow, though
there is a 30% chance winds will remain southerly through the day.
Clouds will increase tomorrow, with a chance of thunderstorms
and gusty outflow winds by later in the afternoon and evening.


.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 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.


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.



UPDATE...Van Cleave
SHORT TERM...Struthwolf
LONG TERM...Barjenbruch
AVIATION...Van Cleave
FIRE WEATHER...Struthwolf

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