Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 162239

Area Forecast Discussion
National Weather Service Salt Lake City UT
339 PM MST Thu Feb 16 2017

.SYNOPSIS...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.


Water Vapor Satellite shows a ridge from southern California into
the Central Rockies. The next storm system is approaching the
Oregon coast. 400-200mb MDCARS wind observations place a 100-145kt
cyclonic jet into northern California and the Pacific Northwest.
GOES/SLC 12Z RAOB/HRRR indicate that precipitable water values
vary from 0.05"-0.10" mountains to 0.20"-0.45" valleys. Blended
Precipitable Water product shows an atmospheric river into the
West Coast with origins from near Hawaii.

Wind gusts have picked up out of the south, ahead of the cold
front currently located near the Nevada state line. Resultant cold
advection across the north will provide enough destabilization for
rain and high elevation snow showers. This activity should wane
overnight as cold advection diminishes.

As the next system cuts off over and drifts southeast over the
eastern Pacific, it will deflect the atmospheric river south of
the Sierras in a more favorable trajectory for southern Utah. The
nose of the Integrated Water Vapor Transport makes its way to
southwest Utah by morning, pivoting from a southwest orientation
to southeasterly as the closed low drops toward the Mexican border
Saturday and Sunday. Though the magnitude of this IVT is not
strong by the time it reaches Utah, the duration is something for
us to monitor as waves of rain and high elevation snow develops
and crosses the region. Warm rain depth is also fairly shallow so
the flood threat is currently not high enough for increased

The first wave of moisture reaches southern Utah late tonight as
diffluence begins to increase. This precipitation is expected to
propagate northward tomorrow and tomorrow evening, with a brief
break overnight.

The next surge of moisture is expected this weekend as the jet
curves northward from Mexico placing the area in a favorable left
exit region. Then the trough passes overhead Sunday. Expecting
more QPF from this second wave, and thus the potential of adding
7-14" of new snowfall above 8kft. A Winter Weather Advisory may be
required as the event nears.

Snow levels look to be around 7kft during the short term period.
Southerly winds increase again Saturday as the closed low
approaches, and may warrant an advisory across the West Desert.

The forecast area looks to begin next week under a somewhat
unsettled pattern. High pressure is progged to build in by Monday,
but lingering moisture will keep some precip going over northern
Utah, primarily over the higher terrain, in warm advection.

By Tuesday, jet support improves over the area, particularly
northern and western Utah, as a broad Pacific storm approaches the
California coast. Shortwave energy moving into the area out ahead of
the system will also aid in the development of precipitation.
However, still think associated precip will be scattered at best
through Tuesday night.

Global models agree that the main system will arrive Wednesday
afternoon and slowly push across the region through the latter part
of the work week. GFS is a bit faster with the system, moving it out
Thursday night/early Friday before high pressure moves in behind it
Friday. The EC keeps shortwave energy on the back edge of the system
over the area through day seven. Have kept in at least chance POPs
through day seven to account for the EC solution. After many days of
unseasonably warm temperatures aloft, this system is expected to
usher in a much colder airmass, with EC/GFS showing 700 mb temps as
low as -10C to -12C by Thursday afternoon.


Surface winds at the SLC terminal are most likely to switch back
to the southeast between 00Z and 02Z, with a chance that
northwesterlies could hold on as late as 03Z. There is a 40
percent chance of rain showers around 01-04Z, which could briefly
bring ceilings below 7000 feet.




SHORT TERM...Rogowski
LONG TERM...Traphagan

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