Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 161148

Area Forecast Discussion
National Weather Service Salt Lake City UT
448 AM MST Thu Feb 16 2017

.SYNOPSIS...High pressure aloft will shift east of the area today
as the first in a series of weather disturbances reaches Utah
tonight. The active weather pattern will continue across the Great
Basin well into next week.


.SHORT TERM (UNTIL 00Z MONDAY)...The recent dry pattern is about
to end as the upper ridge over the eastern Great Basin shift east
of the area later today. The first shortwave to cross the region
currently sits off the Pacific Northwest coast. This feature will
weaken a bit as it races east-northeast across far northern Utah
this evening. Precip associated with this feature should remain
close to the near 700mb baroclinic zone which will settle into far
northern Utah immediately ahead of the shortwave. Precip for the
most part will remain light, and likely end quickly behind the
shortwave late tonight/early Friday.

A secondary area of light precip not associated with the above
mentioned shortwave could work into extreme southwest Utah late
tonight. Weak but somewhat moist low-level warm advection into
southwest Utah supported by a weak mid-level shortwave and the
exit region of the upper jet should be sufficient to generate an
area of light precip across the far south late tonight/early

The next disturbance to impact the region looks to be a much more
substantial system as it moves into the region for Friday
afternoon through Saturday. This next feature will deepen rapidly
off the California coast, with an eventual upper low forming and
tracking east along the Arizona/Mexico border late Saturday
through Sunday.

A deep layer moisture source tapped by this system will advect
into southwest Utah early Friday, then spread across the entire
region by Friday evening. Shortwaves ejecting out ahead of the
strengthening trough along with good upper diffluence should
support fairly deep synoptic-scale lift over the south beginning
Friday, then across portions of the north and east late Friday
afternoon and night.

Shower activity will remain loosely organized Saturday through
Saturday evening as dynamic lift looks to be weak but moisture
quite plentiful. The next system to move in off the Pacific will
reach Utah by Sunday afternoon. This feature will offer up the
best chance for widespread valley rain/mountain snow, especially
across the northern/central portions of the state. The ambient air
mass will still be quite moist as the near 700mb baroclinic zone
works into western Utah by early afternoon. Low-level cold
advection working into the northwest portion of the state along
with increasing dynamic lift from the advancing trough and
favorable jet support in the exit region of the jet all suggest
fairly strong synoptic-scale lift and the potential for widespread
precip. Snow levels will be coming down during the day, though
suspect that all but the highest valley locations will remain in
rain or a rain/snow mix. Mountain locations, especially across the
north will see several inches of new snow with this feature, with
most of the accumulation arriving after the short term forecast

.LONG TERM (After 00Z Monday)...A pattern change will be taking
place during this extended period as we go from a west southwest
storm track into the western CONUS early in the week to a northwest
storm track by the end of the work week. The GFS and EC have a
similar 500mb southwest flow across the region Monday through
Wednesday but the GFS 500mb heights are 120 meters lower than the EC
while the GFS ensemble mean heights are about 60 meters lower than
the EC. The EC has been been trending slower with lowering of the
heights with the GFS playing catch up. Therefore have based forecast
on the EC solution.

With the higher heights across the CWA have backed off on the PoPs
through Wednesday and raised the temperatures a few degrees as well.

By Wednesday night the trough originating in the northern Pacific
will drop southeast and move into the Great Basin with substantially
colder air than past several storm systems which had originated over
the central Pacific. The EC and GFS timing of this system with the
associated 700mb trough axis moving across the CWA Thursday are
remarkably close which added confidence to boost PoPs Wednesday
night into Thursday. With the 700mb temps lowering to -10C degree
and colder, snow levels will come down to most valley floors with
this system.


.AVIATION...Light and variable winds at the SLC terminal early this
morning will become southeast and gradually increase by early
afternoon and remain southerly through the afternoon and evening.
There will be a chance of rain showers after about 02Z tonight.
There is a 40 percent chance that cigs will lower to below 7K ft
after 03Z.





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