Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 181040

Area Forecast Discussion
National Weather Service Salt Lake City UT
440 AM MDT Sun Jun 18 2017

.SYNOPSIS...High pressure will build over the eastern Great Basin
today and remain in place Monday into Wednesday, bringing very hot
temperatures to the region.


.SHORT TERM (through 12Z Tuesday)...A northerly gradient will
remain over the CWA through today as the ridge builds over the
western Great Basin. Despite this northerly flow temperatures
across northern Utah and southwest Wyoming will rise by several
degrees as the forecast for the 700 mb temperatures shows an
increase of about 3 degrees across the north. However, across the
south, the 700 mb temperatures are either cooler by a few degrees
or nearly similar to the 00Z Sunday temps. At Cedar City the 700mb
temps are forecast to be 3 degrees cooler than yesterday while at
Saint George and Lake Powell similar temps are forecast. As a
result, have cooled the southwest some, except for Dixie as the
down sloping northerly flow should allow temps to be within a
degree or two of yesterday.

The PWs across northwest Utah were nearly an inch last evening
while southern Utah the PWs were closer to 0.70 of an inch. Due
to the anticyclonic flow of the high pressure moving in,
subsidence will dry the air mass across northern areas while the
drying will wait until Monday across the south. This air mass
should be thoroughly dried out Monday CWA wide so no mention of
any thunderstorms.

Temperatures will warm by about 3-8 degrees across the region
Monday under this dry air mass pushing temps across southern
Utah into the dangerously hot range. Therefore, the Excessive Heat
Warning and Heat Advisory remain in effect for lower elevations
of southern and southeast Utah beginning Monday.

.LONG TERM (After 12z Tuesday)...Strong high pressure will be
centered over AZ at the start of the long term period with the
ridge axis extending nwd over UT. This places the axis of the
hottest 700 mb temps directly overhead and expect temps Tue to be
the hottest they have been so far this year, ushering in the
summer solstice at 1024 PM MDT Tuesday evening.

Spotty convection is forecast to accompany the thermal ridge
across the CWA with the best chances across the north into Tue

The ridge is forecast to begin to flatten Tue night into Wed as a
low amplitude trof sags into the PacNW and nrn Rockies and a dry
cold front drifts south into the nrn CWA Wed aftn. The GFS has
been more aggressive and faster with the trof and the push of
cooler air south into UT than the EC but less consistent. Have
trended forecasts towards the EC here keeping Wed hot and the
threat of convection mainly north instead of shifting it south per
the GFS.

Both models continue pushing the dry front southward on Thu with
convection shifting to srn UT. Kept a mention over the central
mtns as a nod towards the slower EC. Temps were a blend but did
cool off the north more than 5 degrees while only cooled the
south a little. The current heat highlights go thru Thu and that
appears on track.

The differences persist into Fri and continued to lean towards the
slower warmer EC, but they come into better agreement on Sat with
cooler air covering the CWA and convection shunted off to the
south. They also both indicate the ridge will start to rebuild
over the Great Basin on Sun.


.AVIATION...Winds at the KSLC terminal will be light southeasterly
or just light and variable through the morning then shift back to
the northwest around 16-17Z.


.FIRE WEATHER...A northerly gradient will prevail across the
region today but the winds aloft will not be as strong as
yesterday so winds will be markedly less in the Uinta Basin,
Castle Country and south central areas. Temperatures will warm
several degrees across the north and RH values will be
considerably lower there than yesterday as the air mass dries out
due to the subsidence associated with the anticyclonic flow of the
building ridge. RHs will be in single digits across the southeast
and south through this upcoming week. With strong heating, a
Haines Index of 6 is forecast for the southern half of the area
Monday through Friday.

A little moisture will move in under the ridge Tuesday bringing
the first threat of generally high based thunderstorms over the
higher terrain. This moisture will linger through the week keeping
the threat, albeit limited, continuing through Friday.


UT...Heat Advisory from noon Monday to 10 PM MDT Thursday for UTZ013-

     Excessive Heat Warning from noon Monday to 10 PM MDT Thursday
     for UTZ019-021.




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