Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 162200

Area Forecast Discussion
National Weather Service Salt Lake City UT
400 PM 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.


.SHORT TERM(Through 00z Tuesday)...Noting tightening baroclinicity
over central Nevada this afternoon in H7 analysis, and will
continue to see these trends increase through this evening.
Looking at water vapor the short wave trough rounding the base of
the long wave attm will eject and lift NE across eastern NV
tonight through tomorrow morning, this enhancing this zone prior
to shifting into northern Utah during the morning hours.

Ahead of this will see a rapid spike in h7 winds tonight across
western and northern Utah, with speeds approaching 50kts during
the latter half of the night. The aforementioned tightening of
baroclinicity will drive frontogenesis over eastern Nevada as
well, with rapid pressure falls expected over NW Utah. Do expect
surface winds to increase significantly over the mtns tonight,
with western valleys potentially gusting to advisory criteria in
localized prone spots when forced to surface. Opted not to issue a
wind advisory at this time due to nocturnal timing detracting
from a more widespread impact. Will continue to monitor.

Prior to passage of the near H7 baroclinic zone tomorrow morning,
do expect precip to begin to fill in across the far north tonight
as upper jet dynamics become more favorable within an increasingly
diffluent environment. Areal extent of precip and a transition in
P-type to valley snow or rain/snow mix will occur with frontal
passage Saturday morning, with light accums (2" or less) likely
for much of the central/northern Wasatch front and Cache. As a
whole though, the front will be trending frontolytic with loss of
the upper support as it lifts into the northern Rockies region
limiting valley potential. Mountain snow will pick up in earnest
however as further destabilization combined with modest
orographics should aid. Opted to issue a winter weather advisory
for the central/southern Wasatch for the day (generally 5-10").

The primary impacts from this trough are expected to occur with
the parent low energy as it tracks across the lower Colorado
valley Saturday night into Sunday. This trough will reignite the
baroclinic zone of central then southern Utah during that time,
yielding widespread snowfall (above 4kft) from the Uintas south
to the AZ border, with lower elevation impacts most likely from
Nephi south. For now opted to roll out winter weather advisories
for the mountains of central/southern Utah (generally 6-12"), but
do anticipate the need for some lower elevation zones across
central/southwest Utah and the Swell region as well. Later shifts
will refine details and look at the latest moving forward.

Heights will build rapidly in wake of trough departure late Sunday
through Monday allowing for an end in significant precip.

.LONG TERM (After 00z Tuesday)...Global models are in good agreement
through the Tuesday through Thursday period with a ridge building
into the area Monday night into Tuesday, then transitioning to
southwesterly flow and increasing moisture Wednesday into Thursday.
Although the EC is a bit faster in building the ridge into the area
late Monday than the GFS and Canadian, the only real effect will be
a few degrees difference in temperatures.

The GFS and EC are now both intent on spreading Pacific moisture
into the area by Wednesday afternoon within the mild southwesterly
flow that strengthens ahead of a deepening upstream trough. Abundant
moisture would bring widespread precipitation to the area. Snow
levels will remain on the high side through Thursday. The upstream
trough is then forecast to weaken as it ejects across the western
CONUS. This is where model spread increases. Colder air is forecast
to spread into the area late Thursday night into Friday, but the
extent of this cold air is dependent on how far north the trough
lifts before crossing Utah. Nevertheless, there is a potential for
snow to reach the valley floors on Friday.


.AVIATION...A few passing showers remain possible at the SLC
terminal through around 06z with a 20 percent chance of a brief
reduction to MVFR conditions. Otherwise, expect a clearing trend in
showers and sky cover overnight. South winds will become established
by around 04z.


UT...Winter Weather Advisory from noon Saturday to noon MDT Sunday
     for UTZ009-010-517-518.

     Winter Weather Advisory from 6 AM Saturday to midnight MDT
     Saturday night for UTZ008.




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