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Area forecast discussion 
National Weather Service Salt Lake City Utah
445 am MDT Friday Oct 31 2014

Synopsis...a mild and increasingly strong southerly flow will
remain over the area through early Saturday. A vigorous Pacific
storm system will reach Utah Saturday. Cool and unsettled weather
will remain over the area Saturday night through early Monday.


Discussion...the cold core eastern Pacific trough approaching
130w early this morning will bring a dramatic change in
temperatures and precipitation this weekend. The axis of the trough will
reach the West Coast this evening. A vigorous shortwave rounding
the base of the trough will lift northeast across southern Nevada
early Saturday...then lift quickly north through Utah Saturday

The associated surface cold front will enter western Utah early
Saturday...then lift northeast with the shortwave during the day.
Increasing frontogenic forcing along this boundary late Saturday
morning/afternoon along with strong dynamic lift should easily
support deep convection along the frontal boundary. Substantial
deepening of the surface low over northeast Nevada in the area of
fairly strong upper divergence suggests that the strongest
convection will exist across northern Utah during the afternoon.

Besides the convection winds will be a major issue with this
storm tonight/Saturday. Ahead of the front we will see the typical
increase in southerly winds with the favorable surface gradient
and increasing low-level wind support. Winds could approach Wind
Advisory criteria this afternoon...but suspect that tonight may be
the more likely period for these stronger winds. Because of the
southwest to northeast track of the surface front...the still
strong low-level southwest flow will likely mix down and create
additional strong southerly winds across the western and northern
valleys Saturday late morning through mid-afternoon.

Pattern gets a bit complicated for the balance of the weekend as
the ejecting shortwave pulls away in the northern rockies...
leaving the main trough hanging back across the Great Basin. The
best dynamic forcing will shift into the southern end of the
trough over northern Arizona/extreme southern Utah. The focus of
organized precipitation will remain near the baroclinic zone stretched
out along a southwest to northeast axis through the center of the
state. Increasing instability as the cold air settles into the
state combined with dynamic lift and convergence into the
baroclinic zone should result in significant precipitation near the
boundary Sunday through Sunday night.

North of the baroclinic zone a decent pool of cold/moist air
exists...but the dynamic lift may turn out to be weak between the
exiting system in the northern rockies and the system well to the
south. Looking for instability showers late Saturday night/early
Sunday...with one last weak shortwave bringing some organization
to the precipitation Sunday afternoon and evening. Precipitation type will be
snow at the higher elevations...with a mix of rain and snow
throughout in the valleys. Intensity of the precipitation will likely
determine if snow falls in the lower valleys...with minimal
accumulations expected. Some orographic enhancement to the
snowfall is possible in the mountains...though the mean layer is
not all that strong and may not produce significant enhancement to
snow totals.

Building heights beginning late Monday should signal the end of
precipitation by Monday evening. The upper ridge building in from the
eastern Pacific will bring a period of dry and mild conditions
back to the region through much of the week. A series of
shortwaves moving through the northern rockies will spread some
clouds into northern Utah...with no real threat of any substantial
precipitation during the extended period.


Aviation...southerly surface winds are expected to increase
throughout the day at the kslc terminal. Gusts in excess of 30 miles per hour
are expected this afternoon beginning between 20-22z...a 70 percent


Fire weather...high pressure has started to shift east over the
last 12 hours allowing a strengthening southwesterly flow aloft to
develop this morning. Very warm and dry conditions will persist
today as such but changes will come Saturday into early week as a
cold Pacific storm moves through the region. Southwesterly winds
will ramp up significantly Saturday as a strong cold front pushes in
from the west. This front will bring widespread wetting rains and
high elevation snow to much of the district Saturday afternoon into
the overnight hours...and very gusty southwesterly winds...with
focus across the north. New snow accumulations will generally stay
above 8000 feet with up a to a couple of inches possible. A
secondary piece of the storm will track through The Four Corners
region Sunday into Monday bringing a focused round of precipitation to the
southeast at that time.

High pressure will build back into the district Tuesday through the
end of the week with another round of warm/dry/stable conditions
during that time.


Slc watches/warnings/advisories...


aviation/fire weather...Merrill

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