Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
1018 am MDT Tuesday Mar 11 2014
Synopsis...a cold Pacific storm system will move south through
the Great Basin today. This storm will linger over extreme
southern Utah midweek...then turn east through northern Arizona
Discussion...water vapor loop shows trough is shearing westward
over Great Basin. Amdar 400-250mb wind observations reveal a
cyclonically curved 90- 115kt jet over The Rockies.
GOES/GPS/rap/12z radiosonde observation indicate the precipitable water value ranges
between 0.07" and 0.31".
Lake effect that developed across Davis County overnight...has swung
through Salt Lake County and is now affecting Tooele County. These
showers should become less organzied as daytime diurnal instability
take over. 09z short range ensembles indicate plenty of daytime
instability for new shower development...but minimal chance for
As the trough continues to elongate westward today...we see a bit of
warm advection in the middle levels. More importantly...the Arctic
boundary makes it way through southwest Wyoming to the northern
Wasatch late in the day (per 850-700mb rap saturated equivulent
potential and streamlines). Updated winds to show enhnaced easterly
flow which will make its way to the Wasatch canyons tonight. Also
increased probability of precipitation across the northeast forecast area with accumulations
likely across southwest Wyoming and the Wasatch Mountain valleys.
Northeast and east slopes will be favored in this pattern...and the
advisory may need to be extended through the evening for the higher
Previous discussion follows...
precipitation...mostly in the form of snow...has been on the
increase overnight as the upper trough over the northern Great
Basin tracks slowly south through northern Utah. Increasing
instability as the middle-level cold pool moves through northern Utah
along with dynamic lift has led to moderate to heavy snow across
the northern mountains. Looking at a peak period for snow through
late morning...followed by a fairly steady decrease in areal
coverage and intensity as dynamic subsidence takes hold and the
middle-level cold pool shift south into central Utah/east-central
Nevada. Will leave the current Winter Weather Advisory in
place...though accumulating snows will likely end early this
Northern valley locations so far have come up short on precipitation owing
in part to the fairly dry sub-cloud layer over the area. Increasing
convective precipitation along with continued cooling in low-levels should
allow some measurable precipitation to develop this morning. Do not
anticipate that snow will be an issue in the valleys as ground temperatures
remain warm and the duration of the event should be rather short.
Will mention some accumulating snow for The Bench/foothill
area...though amounts should be on the light side.
As the upper trough continues south it will shear apart over
central/southern Utah with a remnant upper low settling into
southern Nevada/southwest Utah on Wednesday. Early on this upper low
should remain a benign feature as it will be somewhat starved for
moisture. Suspect that isolated convection will form near the low
center in the cold air instability across southern Nevada through
northwest Arizona. With time moisture will work north into extreme
southern Utah...with showery precipitation forming in the developing
deformation zone in the northeast flank of the low. This deformation
should remain somewhat active as the upper low tracks east across
northern Arizona Thursday through early Thursday evening.
Up north the deep easterly flow that develops behind the trough will
create conditions favorable for Strong Canyon winds along the
northern/central Wasatch front. The surface pressure gradient is not
all that favorable for very Strong Canyon winds...so will hold off
any highlights for now. Strong gaps winds across extreme southwest
Utah do looks promising for a brief time late tonight through
Wednesday. Strong northeast cold advection along with tight
northerly surface gradient will support strong winds. This event
will likely be short-lived as the deepening upper low over southern
Nevada turns the upper winds more easterly with time.
High pressure building near the West Coast late in the week will
leave the Great Basin under a northwest flow heading into the
weekend. Embedded shortwaves will graze northern Utah
Friday...though with little moisture and minimal thermal and dynamic
support for lift do not see any good reason at this time to expected
significant precipitation across the far north Friday.
A weak system will move through northern Utah Saturday...bringing
light precipitation to the northern mountains. Though there are differences
in details...both the GFS and ec agree that this Saturday system
will bring precipitation to northern Utah...and so increased mountain probability of precipitation
on Saturday. Models begin to diverge early next week...as the ec
brings a strong cold front through the state on Monday...while the
GFS keeps the front well to the north of the state. Because of this
disagreement...did not make any significant changes to the grids in
the extended period.
Aviation...winds will remain from the north through the day at the
slc terminal. Vcsh to prevail with afternoon warming taking place. Ceilings
will permanently lift above 7000ft between 21z and 00z this
Utah...Winter Weather Advisory until 6 PM MDT this evening for
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