Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 202228

Area Forecast Discussion
National Weather Service Salt Lake City UT
428 PM MDT Mon Mar 20 2017

.SYNOPSIS...A series of weak weather disturbances embedded in the
southwest flow aloft will impact Utah through Wednesday, The
pattern will turn more active during the latter half of the week,
and remain active through the upcoming weekend.


.SHORT TERM (Until 00z Friday)...The well-defined upper level
trough currently between 130-140W will move slowly east, reaching
the west coast early Wednesday. Ahead of this trough a series of
weak shortwaves will eject northeast across the Great Basin and
impact Utah through at least early Wednesday.

The first in the series of shortwaves is currently moving across
northern/central Utah. Loosely organized weak convection from
earlier today has become organized along the shortwave axis, with
the most active area underneath modest upper divergence along the
spine of the Wasatch range and extending northeast into the
western Uintas. This feature will weaken a bit as it exits the
forecast area by early this evening. Weak upstream convection
could linger for awhile early this evening, but should end before
midnight tonight.

Isolated convection across southern Utah has already ended across
southwest Utah, with little evidence of any further active to the
west. This convection should end late this afternoon or early this

Additional shortwaves ejecting out of the eastern Pacific trough
should bring additional isolated/scattered convection to mainly
northern/western Utah on Tuesday. This convective activity may
get a boost Tuesday night/Wednesday as cooler mid-level air
advances east out of Nevada and into west-central and northwest
Utah. Suspect that organized convection will form along the weak
near 700 mb baroclinic zone that settles into northwest Utah
Tuesday night.

Increasing low-level southerly flow ahead of the upper trough
along the west coast Wednesday will turn the low-level baroclinic
zone back into eastern Nevada. Convection will become terrain-
based during the afternoon, then expand fairly quickly as the west
coast trough clears the Sierras and settles into Nevada.
Widespread precipitation will develop Wednesday night as dynamic
lift and strong thermal advection take hold ahead of the advancing

The heaviest precip early into the storm will concentrate across
southern/central Utah in the area of strong dynamic and thermal
support for synoptic-scale lift. The focus will shift into
northern Utah Thursday as the trough axis moves through the area
and a developing cold northwest flow takes advantage of the
terrain to generate significant snows for the northern mountains
and widespread rain/snow for the adjacent valleys. Precip will
begin to wind down from the west as drier air and dynamic
subsidence trail the trough axis through the state.

.LONG TERM (After 00Z Friday)...The trough continues to slide
eastward through Thursday night, and is well east of the area by 12Z
Friday. A few showers may linger in the eastern half of the CWA
Thursday evening, but otherwise expect a fair drying and warming
trend through Thursday night and Friday, as ridging re-builds over
the Great Basin.

The pattern remains progressive heading into the weekend, with
another storm moving into the region on Saturday. There are still
some timing differences in the models, but the best chance of
precipitation for much of the CWA looks to be Saturday afternoon
and/or evening. Have generally increased POPs through this period,
with good agreement at the moment that the core of the upper trough
will move over the Utah/Arizona border late Saturday, and snow
levels will lower to 6000-7500 feet by Saturday night.

Timing differences begin to increase starting Sunday, but the global
models generally have the idea of a wetter/cooler/more progressive
pattern continuing through at least Monday. Have kept POPs somewhat
elevated and temperatures near climatological normals through the
end of the extended forecast.


.AVIATION...Northerly winds are expected to continue at the SLC
terminal through 02-03Z, shifting to the southeast after that time.
Showers are expected to remain largely away from the terminal but
there is a 10 percent chance of briefly erratic winds near any
showers in the vicinity.





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