Scientific Forecaster Discussion
fxus65 kslc 102313
Area forecast discussion
National Weather Service Salt Lake City Utah
413 PM MST Sat Dec 10 2016
Synopsis...a moist westerly flow over the region will dry out on
Sunday. Additional moisture will spread back into the area on
Tuesday and persist through the end of the week.
Short term (thru 12z tuesday)...strong moist westerlies continue
over the nrn County Warning Area this aftn. Precip has remained fairly widespread
in the valleys south to about Nephi with mtn snow noted south to
Snow levels are hovering around 6000 ft but will start to lower
from north to south behind a cold front working its way into the
County Warning Area. Expect precip to turn showery across the north as the colder
air spreads in and it changes to snow. This should limit the
amounts across the far north and in the Cache Valley and have
opted to not issue any winter weather highlights for these
valleys, altho local slushy roads could briefly develop.
Snow will continue across the mtns as well as swrn Wyoming with roads
becoming snowy again between now and sunset. Existing winter
weather warnings and advisories remain on track.
Expect similar developments in the Wasatch mtn valleys with roads
also becoming snowy by dark. The winter driving conditions will be
expanding to the lower elevation valleys as snow levels drop
with the advancing cold air. Have added this zone to the Winter
Weather Advisory suite.
The precip will spread into central and srn Utah during the night
weakening as it GOES. This could produce some minor travel
impacts over the summits along I-15 and over the central and srn
mtns but most valleys will stay just rain.
The fast westerlies will persist but drier conditions spread over
the area by midday sun as the low amplitude wave currently
crossing the Great Basin slides east. Another weak flat wave
ripples past Mon with maybe a little precip lingering along the
The flow starts to buckle Mon night as low amplitude ridging
develops over the W coast and a warm front forms over the nrn County Warning Area.
Long term (after 12z tuesday)...the global models have finally
come into very good agreement with each other at the beginning
of this long term period. Both models show a moderate warm
advection pattern penetrating across northern Utah and southwest
Wyoming during the course of the day Tuesday which is associated
with a weak disturbance in the southern stream moving rapidly
eastward across the northern Great Basin. The impacts from this
system will be across the northern third or half of the County Warning Area.
In the wake of this disturbance, the GFS more so than the ec,
pumps the ridge up across the County Warning Area Wednesday into Thursday. Have
trended the pops northward during this period, especially
Wednesday night. The 700 mb temperatures warm to between 0 and -3
across northern portions of the County Warning Area so that all valleys with pops
will have rain rather than snow and even the mountain valleys will
have a better chance for rain than snow as snow levels rise to
near 7 kft. Have warmed temps by several degrees for Wednesday and
This ridge is short lived as the long wave trough reestablishes
itself over western Canada and it intensifies the trough off the
pac northwest coast and swings a full latitude trough across the region
Thursday night through Friday according to the GFS. The ec keeps
the pac northwest trough separate from the developing long wave trough.
Not sure which is the correct solution but either way, a
significant widespread precipitation event is expected Thursday
night into Friday. Have gone with likely pops across much of the
County Warning Area Thursday night. Much colder air will move in behind this
system with the GFS showing -20c 700 mb temperatures over northern
Utah with -10 to -12c over southern Utah by Saturday morning. The
ec, which was very cold on its previous 00z run, has backed off to
-16c over nrn Utah while about -12c over srn Utah. Have leaned
toward the ec for now as MOS guidance supports somewhat less
frigid temps for Friday.
Aviation...northwest winds have overspread the kslc terminal and
should persist through the evening push. There is a 30 percent
chance that the winds will Switch Back to the south for a few
hours overnight. MVFR visibilities are expected at times in rain
this evening and then possibly in a rain/snow mix after 0800 UTC.
No snowfall accumulations are expected.
Utah...Winter Weather Advisory until 9 am MST Sunday for utz006-010.
Winter Storm Warning until 9 am MST Sunday for utz007>009.
Wyoming...Winter Weather Advisory until 9 am MST Sunday for wyz021.
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