Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 122220

Area Forecast Discussion
National Weather Service Salt Lake City UT
420 PM MDT Tue Sep 12 2017

.SYNOPSIS...A series of storm systems will bring cooler and
wetter conditions to Utah and southwest Wyoming for the second
half of the work week, with drier conditions returning for the


.SHORT TERM (Through 00Z Friday)...Scattered showers and
thunderstorms continue across Utah this afternoon, with the best
focus of storms over central Utah as of 21Z. Earlier today, a wave
moved across northwest Utah, creating good coverage of
thunderstorms across the west desert, before it started pushing
off to the north. These storms also produced some outflows that
moved across the Great Salt Lake and into the Wasatch Front,
generally producing winds 30-45 mph, but other than Utah County
the Wasatch Front has remained pretty stable so far today.

The previously mentioned disturbance over northwest Utah could
help keep some convection going across northern Utah overnight, as
it rotates around the north end of the Four Corners ridge and
slides eastward across Idaho/Wyoming. Starting on Wednesday,
moisture and instability start to increase across the area ahead
of a closed low moving into the Great Basin. Increased cloud cover
will probably cool temperatures a few degrees on Wednesday
compared to today, but otherwise any significant cold advection
holds off until Thursday/Friday.

Models have generally locked into the idea of the core of the
closed low moving through southwest Utah on Thursday morning, and
then across eastern Utah Thursday afternoon. Meanwhile, northern
Utah also looks to have an increase in precipitation Thursday
afternoon, as it starts to get under the influence of the larger
trough dropping in from the northwest.

.LONG TERM (After 00Z Friday)...The closed low will be ejecting out
of the forecast area Thursday night as the northern branch trof digs
to our west. Increasing dynamic lift over the northern CWA ahead of
the digging trof is forecast to generate fairly widespread precip
over the northwest as it works on moisture left behind by the
ejecting low. The associated cold front will arrive Fri morning and
push slowly south thru the CWA over the next 24 hours. This front
should be accompanied by a broad swath of precip that looks to
persist across portions of the north thru much of the day. Snow
levels will be dipping to the highest peaks Fri and temps will drop
20 to 30 degrees from highs today.

The precip will be winding down and turning showery Fri night with
instability showers expected Sat in the base of the cold trof.
Snow levels will dip to 8-9Kft in these showers but any accumulations
will be spotty and light.

The trof exits the region by Sat night with a quick return to mild
swly flow for Sun as a deeper trof develops off the PacNW coast.

The global models are in rough agreement bringing this deep cold
low into the western states early next week altho differ in the
details and timing of the associated cold front. Leaned towards
the slower EC as GFS appears a bit too aggressive with the
development on this low inland.


.AVIATION...Northwest winds at KSLC will continue into this
evening then switch to southeasterly after about 03-04z but there
is a chance this switch will hold off until 05-06z. There is also
a chance that passing showers will bring brief gusty/erratic
winds to the terminal through the night.


.FIRE WEATHER...Scattered showers and thunderstorms across Utah this
afternoon could continue into the overnight hours, especially across
northern Utah. Coverage of thunderstorms will increase both Wednesday
and Thursday, as a low pressure system moves across the Great Basin.
Southwesterly winds will be breezy on Wednesday and Thursday, but a
moister airmass means that widespread critical conditions are not
currently expected.

The chance of wetting rain increases through the end of the week,
especially Friday as a fall cold front moves through the area, and
snow accumulation is even possible near mountain peaks. This is the
beginning of a larger pattern change, and generally cooler and wetter
weather is expected heading into next week.





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