Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 132323

Area Forecast Discussion
National Weather Service Salt Lake City UT
423 PM MST Fri Jan 13 2017

.SYNOPSIS...An upper level low will move east across northwest
Mexico through Saturday, with moisture reaching into southern Utah.
In the wake of this low, a drying trend will follow into early
next week. A more active pattern will redevelop by the middle of
the week.


.SHORT TERM (Through 00z Tuesday)...An upper low situated off the
southern California coast continues to drift southward this
afternoon as it becomes cut off from the mean flow. Meanwhile
further north a weak shortwave trough is noted translating through
the northern Rockies as it brushes the far northern Great Basin.
As the upper low continues to drift southward, and further away
from the forecast area this evening, upper diffluence along with
moisture transport will continue to diminish across southern Utah
bringing a temporary end to any lingering precipitation across
the south. Meanwhile further north, drier air associated with the
northern stream trough is expected to help erode cloud cover
overnight across northern Utah and southwest Wyoming, and if skies
do clear out patchy fog will be possible given ample boundary
layer moisture, including along the Wasatch Front.

The upper low is forecast to gradually pivot and turn east
overnight, eventually translating east across the Baja region
Saturday, and northwest Mexico Sunday. As this happens, moisture
is forecast to spread back into southeast and south central Utah
as early as tonight, with the best chance for precipitation coming
Saturday afternoon into Saturday night. Snow levels should remain
in the 5500-6000 foot range through this time. Increased POPs
10-20 percent across south central and southeastern zones through
Saturday night.

Otherwise, with light flow and gradually warming temps aloft,
valley inversions will slowly strengthen across northern and
central Utah into early next week. As such have gone with steady
or slowly declining temperatures across the valleys of northern
Utah into early next week.

.LONG TERM (After 00Z Tuesday)...Sharp upper level ridge axis
overhead Tuesday shown by global models will enhance the valley
inversion across the region keeping valleys colder than adjacent
mountains by a good 8-15 degrees across the north and 5-10 degrees
across the south. This strong ridge will begin to break down
Wednesday as the westerlies punch in across the wrn CONUS. The EC
is faster with moisture spreading in across northern Utah than the
GFS and this seems too fast as both the EC and GFS have been
trending sharper and deeper with the Thursday trof. Considering
this trend, have backed off on PoPs on Tuesday night and Wednesday
more in line with the CONSALL guidance. The onset of precip will
likely be a challenge once again with some pockets of freezing
rain/snow before going over to all rain in the valleys through
Thursday. Snow levels are expected to rise to near 8000 ft late
Wednesday night but then lower back down to near 6000 ft Thursday

The models are in pretty good agreement with a sharp trough
moving through the CWA Thursday into Thursday night. With the
atmospheric attached to this system confidence of widespread
precipitation across most of the CWA has increased and
consequently have boosted many PoPs up to likely. The temperatures
at 700mb fall below -9C across northern and western portions of
the CWA by late Thursday night for snow down to the valley floors.
In the wake of this trough, a weak ridge is forecast by both the
GFS and EC for Friday, but the active westerlies will bring
another storm system in across the region late Friday night and


.AVIATION...VFR conditions are expected to prevail at KSLC through
the evening before visibility becomes reduced into the MVFR
category overnight. There is a 40 percent chance of fog reducing
visibility to less than one half mile between 10-15z Saturday.
Otherwise Ceilings will remain in the 6-7 kft range through the
evening before scattering out. Winds are expected to remain light
northerly through the TAF period.





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