Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 161602

Area Forecast Discussion
National Weather Service Salt Lake City UT
1002 AM MDT Fri Mar 16 2018

.SYNOPSIS...The broad upper level trough across the western
states will maintain cool and unsettled conditions across Utah
this weekend. High pressure aloft will return for the first half
of next week and bring a warming trend to the region. Another
storm system will impact the region during the latter portion of
the week.


.DISCUSSION...Heights will continue to build aloft today as the
departing trough continues to progress downstream, and the deeper
parent low remains upstream centered over the CA/OR border. Will
note backing flow aloft and a net increase in H7 winds this
afternoon as the influence of the latter becomes more apparent as
it slowly progresses inland and towards the Great Basin area.

Do note existence of residual low level moisture in the 12z KSLC
RAOB (largely below H7) with suitable lapse rates to maintain a
chance of convective snow showers over the higher terrain. Further
destabilization of the column aided by daytime heating will be the
primary driver for this. As a whole though, quite a nice early
spring day is on tap across the area with near seasonal temps and
good mixing.

Although the western valleys will see a net uptick in southerly
winds this afternoon/evening, peak H7 winds coupled with rapid
pressure falls will occur overnight into Saturday morning...this
as the mid level baroclinic zone coincident with the approaching
low transitions across Nevada (overnight) and into the far west
(by dawn). Could see some nocturnal gusts to advisory level
criteria in the prone areas of the western valleys, but these
should remain intermittent and localized.

As the upper trough settles into the central Great Basin tonight a
short wave shearing off from the parent low will lift NE into the
northern Great Basin/Rockies region. Favorable upper jet position
coupled with increasingly diffluent flow aloft will generate
enough lift for showery precip across the far north tonight
(largely UT/ID border region) as this begins. Progression of the
wave will aid to surge the near H7 baroclinicity across northern
Utah Saturday morning bringing the best chance of precip (largely
snow) attm. Focus of this should occur along the northern Wasatch
Front/Cache/Bear River mtns coincident with the tightest thermal
packing and proximity to the short wave, while further south the
push continues to look more frontolytic and less significant for
accumulating snowfall.

Primary focus this shift will be to key in on the wind potential
tonight, and potential for accumulating snowfall over the far
north Saturday morning. Thereafter will delve into the further
evolution of the trough as trends continue to point towards
increased consolidation across central/southeast Utah Sat night
into Sunday. Previous discussion below.

.PREVIOUS DISCUSSION...Meanwhile a secondary shortwave is
forecast to rotate through the lower Colorado River Valley and
Desert Southwest Saturday night into Sunday, bringing snowfall to
much of southern and central Utah above 4000 feet. Southern
portions of the Wasatch Front may find themselves on the northern
fringe of this precip shield. Have increased PoPs substantially
across central and southern Utah during this timeframe, while
cutting back PoPs in the north. Rising heights on the back side of
this departing system should allow for a drying trend Monday.

Zonal flow will be in place to start the long term forecast. A
shortwave is expected to cross northern Utah Monday night into
Tuesday, though at least one operational global model would keep
this shortwave further north and east with little impact to the
CWA. This will be followed by a period of shortwave ridging

Attention then turns to a fairly significant trough that will
impact much of the Southwest later Wednesday into late Friday or
perhaps early Saturday. Model trends continue to indicate this
system has the potential to tap into Pacific moisture around the
southern portion of the Sierras. Research has shown when this
occurs, heavy precipitation is possible. Given how far out this
system is, it`s something to monitor rather than to forecast at
this point. Confidence is increasing, however, that a widespread
precipitation event will occur across much of Utah Thursday into
Friday. Given the trajectory of this system, snow levels are
currently expected to be high.


.AVIATION...Southerly winds are expected to continue through the
day at the SLC terminal with only a 20 percent chance winds will
become either light and variable or light northerly between
21-01Z. Ceilings are expected to predominately remain above 7000
feet AGL through tonight.





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