Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 221021
Area Forecast Discussion
National Weather Service Salt Lake City UT
421 AM MDT MON AUG 22 2016
.SYNOPSIS...Moisture will continue to spread northward across
southern and eastern Utah today, then remain in place on Tuesday.
Meanwhile, an upper level disturbance will drift slowly across
the region, allowing drier air to spread over Utah on Wednesday.
.SHORT TERM (THROUGH 18Z THURSDAY)...The large-scale pattern this
morning indicates a ridge axis over the northern Great Plains while
an upper low spins over southern British Columbia. Meanwhile, an
elongated trough axis extends from off the central California coast
through the Four Corners region with several weak embedded
circulation centers. One such low center is located over far
northwest Arizona. Ahead of this low, southerly flow has drawn
moisture into southern Utah.
As the circulation slowly lifts into southern Utah today, moisture
will continue to increase across southern and eastern Utah with PWAT
values forecast to increase to close to 1 inch along the Arizona
border. Showers and thunderstorms will increase in coverage today
and become increasingly wet as a result. Although models indicate
PWATs will increase across northern Utah as well, this moisture will
not be very significant or deep, since westerly flow will be
The aforementioned British Columbia low will track eastward and,
combined with additional disturbances rotating around the back side
of the low, will allow a mean trough to set up over the PacNW and
northern Rockies tonight into tomorrow. A drier west to northwest
flow aloft will start to spread into the area tomorrow, with a
stronger push on Wednesday. This will force the moisture to retreat
to the southeast. In addition, temperatures will see a cooling trend
across the north tomorrow and Wednesday as a cold front pushes into
.LONG TERM (AFTER 18Z THURSDAY)...Models continue to dig a trough
southward into California on Thursday, with upper level disturbances
ejecting into the Great Basin Thursday and Friday. The trough shifts
winds southwesterly, advecting moisture into southern Utah on
Thursday and across a greater extent of the forecast area by Friday.
Ample CAPE and instability combine with PWATS near .75 inches to
encourage the potential for showers and thunderstorms over southern
Utah on Thursday and spreading northward on Friday. As such have
lowered temps a few degrees throughout the forecast area for these
The trough shifts eastward across the Great Basin on Saturday,
continuing potential for convection across Utah into the weekend.
Global model solutions diverge for the latter half of the weekend,
with the ECMWF bringing a drier airmass on Sunday while the GFS
doesn`t shunt the moisture tap until Monday. Have thus added some
PoP values for Sunday across the south/central/NE mountains.
.AVIATION...VFR conditions with southerly winds expected at KSLC
through the morning hours. Winds are expected to shift to the
northwest between 19-20z with a 30 percent chance of delaying until
.FIRE WEATHER...Deeper moisture will continue to spread into southern
Utah today aided by a weak disturbance along the Utah/Arizona
border. Scattered showers and thunderstorms will become increasingly
wet today across southern and portions of eastern Utah as a result.
Across northern Utah, this moisture will not nearly be as deep so
expect little more than isolated dry thunderstorms. A drier
northwesterly flow will begin to spread into the area tomorrow. This
will cause the airmass to dry north to south tomorrow through
Wednesday. Moisture looks to return Thursday afternoon and may
linger through the weekend.
WY...Red Flag Warning in effect from noon to 9 PM MDT Monday
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