Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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209
FXUS65 KSLC 231032
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
432 AM MDT TUE AUG 23 2016

.SYNOPSIS...Moisture will remain in place across southern and
portion of eastern Utah today as an upper level disturbance drifts
slowly across the southern reaches of the region. A northwest flow
will usher in drier air across the forecast area on Wednesday.
Moisture will make a quick return Thursday and remain in place
through the end of the week.

&&

.SHORT TERM (THROUGH 18Z FRIDAY)...An upper low is tracking east from
southern Alberta into Saskatchewan this morning, with its associated
trough axis extending into central Idaho. This trough has pushed a
weak boundary into northern Utah with a drier westerly flow behind
it. Meanwhile, a moist airmass remains in place across southern Utah
where PWATs are around 1 inch along the Arizona border. A
circulation center is noted near the Arizona strip and this
continues to help drive scattered weak showers across portions of
southern Utah early this morning.

This circulation center is progged to slowly track east today,
maintaining a threat of convection through the day across mainly the
southern through east-central portions of the forecast area. With the
mean flow remaining relatively weak, these storms will again be
capable of producing locally heavy rain. Any storm propagation will
likely be to the south this afternoon, which would take them down
drainages should any develop over prone areas across the far south.
While this is a flash flood threat, the limiting factor would be
cloud cover, which remains fairly thick this morning. Anticipating
that it would take a while for the clouds to thin out enough to
enable deeper convection and thus intense rainfall, have opted to
hold off on any flash flood watches.

Temperatures are expected to be a few degrees cooler today for most
areas, due in part to the cold advection across the north and the
moisture across the south. This will bring readings close to climo
for many northern Utah sites while southern Utah will be cooler than
normal.

A secondary push of cooler air is expected this evening into
tomorrow as a shortwave trough embedded within the mean trough
carves into southern Idaho. As a result, temperatures will continue
to trend downward across northern Utah. However, temperatures in
southern Utah may actually rebound as more significant drying will
take place tomorrow. Isolated showers and thunderstorms may still
develop over the southern mountains tomorrow, but overall the
weather will be much less active.

Another shortwave disturbance embedded within the mean trough is
expected to carve into the northern Great Basin on Thursday. The
resultant southwest flow will draw some moisture back into the area
which, combined with large-scale lift and instability associated
with the trough will result in increase shower activity once again.

.LONG TERM (AFTER 18z FRIDAY)...Positively tilted upper level
trough poised over the Northern Rockies pushes another disturbance
into the forecast area on Friday. This system entrains moisture
further north and offers another round of instability to encourage
showers and thunderstorms over much of forecast area by Friday
afternoon. Temperatures will likely run about 5 degrees below
seasonal norms.

Global models in better agreement about passing a trough through the
area on Saturday, continuing the chance for convective showers and
thunderstorms into Saturday night. Models have swapped a bit in
timing the return of a drier, more stable airmass, with the GFS
ahead and more staunch. Have thus reduced PoPs a bit more for Sunday
and eliminated them for the beginning of the workweek. Temps climb
to or just above norms by this time.

&&

.AVIATION...Southeast winds at KSLC will prevail into the late
morning before switching back to the northwest between 18-19z.
VFR conditions will prevail through the TAF period.

&&

.FIRE WEATHER...A moist airmass will remain in place across the
southern and eastern portions of the fire district today. The
potential for wet thunderstorms will persist there, and locally
heavy rain will be possible. Meanwhile, a cooler and drier northwest
flow will spread into northwest Utah today. Winds will increase
across the higher terrain of northern Utah today, and combined with
low humidities will lead to critical fire weather conditions. The
drier airmass will spread south and encompass much of the fire
district tomorrow. Moisture will then return to the area Thursday
and remain in place through Saturday.

&&

.SLC Watches/Warnings/Advisories...
UT...Red Flag Warning from noon today to 9 PM MDT this evening for
     UTZ479.
WY...Red Flag Warning from noon today to 9 PM MDT this evening for
     WYZ277.

&&

$$

Cheng/Verzella

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