Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 161024

Area Forecast Discussion
National Weather Service Salt Lake City UT
424 AM MDT Sat Sep 16 2017

.SYNOPSIS...A cool airmass will reside across the region today,
followed by a warming trend Sunday into Monday. The next cold
front will cross northern and central Utah Tuesday, bringing
another shot of cooler air.


.SHORT TERM (Through 00Z Tuesday)...Early morning satellite
imagery and objective analysis show an upper low spinning over the
northern Rockies, with a shortwave trough rotating around the base
of this low across far northeast Utah into southwest Wyoming.
Large scale ascent associated with this trough has largely
shifted east into Wyoming, with mid/upper level drying noted in
water vapor imagery. As this wave and parent low lift away from
the region today, shortwave ridging will temporarily build across
the forecast area, allowing for dry and stable conditions.
Temperatures will remain below seasonal norms, particularly across
the north where max temps are expected to run 10 or more degrees
below climo.

A weaker shortwave trough is forecast to translate through the
northern Great Basin tonight into Sunday morning. Although weak,
large scale forcing associated with this wave and associated jet
streak will bring a chance for showers to the mountains of
northern Utah Sunday morning, spreading into central Utah Sunday
afternoon. Low level warm advection coupled with a modifying
airmass should allow max temperatures to trend upwards several
degrees across the forecast area Sunday afternoon.

Increasing southerly flow is expected to develop Monday ahead of
a stronger upstream trough. This flow coupled with warming aloft
and better mixing should allow max temperatures to warm to near or
above climo Monday afternoon across the forecast area.

.LONG TERM (After 00Z Tuesday)...A progressive late autumn weather
pattern will continue through this extended time frame. The EC is
the model of choice as it moved toward the 12Z GEFS solution being
slower in bringing in a cold trough and associated cold front
Tuesday morning. This timing is critical as to the forecast high for
the day will be. Most models showed forecast values in the mid 60s
for Monday at SLC and this looks reasonable but if the cold front
would arrive a couple of hours earlier then forecast temperatures
could be several degrees too warm over northern Utah Tuesday. Also
with the slower arrival time have backed off on the PoPs for Monday
night. The best 700mb cold advection comes between 12Z and 18Z
Tuesday, therefore boosted PoPs during this period from about Provo
northward as this storm system will largely only impact northern

A break between systems comes Tuesday night into Wednesday,but
another system comes into the area Wednesday night. The GFS is a
little farther west with the 500mb trough by Thursday. Therefore the
better dynamics associated with the system move across the central
and northern Utah according to the EC vs the GFS. Have leaned
towards the EC and have greater PoPS due the better dynamics; i.e.
300 mb jet, 500 mb vorticity and 700mb baroclinic zone which is
going through fronto genesis as it moves across Utah. Have
boosted PoPs accordingly.

Temperatures will run 10-25 degrees below normal during this


.AVIATION...Southeasterly winds at the KSLC terminal will shift
back to northwest between about 16 and 18Z. VFR conditions will


.FIRE WEATHER...A cool, dry, and stable airmass will remain in
place across the region today in the wake of a departing storm
system. A weaker system will cross the area Sunday, bringing a
chance of showers and thunderstorms primarily to the higher
terrain. Meanwhile the airmass will modify a bit, allowing for a
warming trend across most locations. Southerly winds are expected
to develop Monday ahead of another approaching system. These winds
may gust into the 30 mph range across western Utah Monday
afternoon. Additionally, with the increase in south winds
temperatures will rebound to near or above normal values Monday.
A strong cold front is expected to cross northern and central Utah
Tuesday, knocking temperatures back below normal for most
locations. Any precipitation with this system is not expected to
be significant, and will likely remain confined largely to the
higher terrain of northern Utah.





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