Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 291023
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
423 AM MDT Thu Sep 29 2016

.SYNOPSIS...A weakening weather disturbance will track north
across Utah this afternoon through this evening. A cold Pacific
storm system will enter the Pacific Northwest early Saturday, then
strengthen as it settles into the Great Basin by early Monday.
This storm system will impact much of Utah during the early
portion of the upcoming week.

&&

.SHORT TERM (Until 06Z Monday)...The remnant of the decaying upper
low currently over southern Nevada will track north through
western Utah today, then into western Wyoming this evening. This
feature will be moving through a decent moisture field (PWAT
values around .75 to 1.00 inches). This combination of weak
dynamic lift and abundant moisture will lead to increasing
convection this afternoon. South-central and southeast Utah could
see some deep convection where the upper level divergence is
strongest. Looking at the potential for locally heavy rainfall in
those areas, with some flash flooding possible in areas prone to
such events.

Moisture will be slow to clear out of Utah Friday. Will likely
see an increasing trend in mainly terrain-based convection during
the day, though not anticipating strong/organized convection at
this time due to the lack of significant dynamic/thermally driven
lift.

A next upper level trough will reach the Pacific Northwest early
in the upcoming weekend. This feature looks to be quite potent,
with a well-defined closed low settling into the western Great
Basin late in the weekend. Ahead of this feature an increasing
southwest flow will serve to maintain breezy conditions and
temperatures above early October norms. Somewhat drier air will
move into the area, though still could see some terrain-based
convection firing up Saturday afternoon. Potential shortwave
energy ejecting out of the main upper level trough could bring
some organized convection to mainly northwest Utah Sunday
afternoon and evening.

.LONG TERM (After 06Z Monday)...Global model consistency regarding
the amplification and net evolution of the next pacific trough seems
to be coming more in line. In the big picture, the idea of a
somewhat less progressive and more amplified system tracking across
the eastern Great Basin early next week is winning out, solutions
similar to those represented by the EC ensemble mean and some
members of the GEFS from days prior. Though details will continue to
unfold in time, do expect a relatively cold and wet system to impact
the north early next week, with primary impact across the north.

A strong cold front is expected to pass across the forecast area
Monday, this as yet another closed upper low carves into Nevada then
points east across the state Monday into Tuesday. With more
consistency in guidance run to run and model to model, have noted an
uptick in QPF as a combination of large scale forcing and modest
moisture combine within the period of cold frontal passage on
through mid level axis passage. With higher confidence coming to
form, opted to raise PoPs fairly significantly across namely
northern and central portions of the area. H7 temps as cold as -6C
should support snow accumulations across the northern mountains once
again, with snow levels potentially lowering to or just below 7000ft
across the north.

Still not overly confident on track and evolution of the trough
Tuesday on, though global guidance does suggest a somewhat
progressive easterly translation through midweek. Have trended grids
along these lines, but wouldn`t be overly surprised to see things
slow down a touch in later runs. Time will tell.

&&

.AVIATION...Southerly surface winds are expected to be maintained
at the KSLC terminal through late this afternoon, then a 60 percent
chance exists for a brief switch to the northwest in the 22-02z
window. Broken mid level clouds and showers are expected to remain
in the vicinity of the terminal, with likelihood greatest around the
arrival gates. This said, not expecting a significant impact
directly to the terminal today allowing VFR conditions to prevail.

&&

.FIRE WEATHER...Remnants of a shearing low will continue to lift
through the area maintaining elevated levels of mid level moisture,
with a gradual moistening trend down to the surface namely across
the east. Scattered showers and storms will remain possible in this
environment today with areal coverage greatest across the central
and eastern portions of the district where wetting rains are
possible. Southwesterly flow aloft will gradually increase over the
next 24 hours allowing a net drying trend across the west, but
moisture across the east will be slow to erode maintaining a more
isolated precip threat across those locales through Friday.

A much stronger and colder system is expected to approach the
district this weekend allowing a further drying trend across the
western valleys, and a net uptick of southwesterly surface winds.
This storm is expected to surge a cold front through the area by
Monday morning bringing an elevated threat of wetting rains to
namely northern and central portions of the district, and the
potential for high elevation snow accumulations to the northern
mountains.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

Conger/Merrill

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