Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 111058
Area Forecast Discussion
National Weather Service Salt Lake City UT
358 AM MST Wed Jan 11 2017
.SYNOPSIS...The next eastern Pacific trough will track east
across the Great Basin today. One final disturbance will impact
the south tomorrow into Friday, followed by high pressure for the
.SHORT TERM (THROUGH 00Z SATURDAY)...
Water Vapor Satellite shows the next storm system crossing Oregon
and Northern California, with a tight circulation rounding the
corner, soon to trail the first storm. 400-200mb MDCARS wind
observations place a 140-160kt Westerly jet over central
California and into the Central Rockies. GOES/SLC 00Z RAOB/HRRR
indicate that precipitable water values vary from 0.15"-0.30"
mountains to 0.40"-0.60" most valleys.
No changes to going headlines. Contemplated a wind advisory for
Western Uinta Basin, south central Utah and the San Rafael swell
but kept gusts just below criteria. Next shift will likely have to
look into some winter advisories for central and southern Utah for
the next storm system.
Warm advection underway as the lead wave approaches from southwest
Idaho and central Nevada. There may be some jet coupling between
the right entrance region of a departing jet and left exit region
into the next one already nosing into southern Utah. This has
lead to an uptick in precipitation area and intensity.
The passage of the wave this morning will usher in the beginning
of 700mb cold advection, though the best cold advection occurs
tonight, leading to snow levels falling to the valley floor.
SREF indicates instability developing this afternoon with
microphysics potentially supporting thunder. Have placed a mention
of thunder in the forecast.
The remaining Pacific energy will enter California tomorrow morning,
cutting off the storm. Warm advection will develop further south,
likely over Central Utah, increasing precipitation chances there.
Precipitation fills in across much of Central and Southern Utah
Thursday afternoon and night as diffluence aloft increases.
With the cyclone position to our southwest, will have to keep an
eye on 700mb cold advection/winds and pressure gradient for
potential of canyon winds both Wasatch Front and eventually Dixie.
There is a 10-12mb northerly gradient across Utah tomorrow night,
however synoptic flow supports splitting of arctic airmass
eastward along the Canadian border as opposed to building westward
across Wyoming. This will minimize the threat of strong gusty
winds with this system.
Global models slower with the progression of the cutoff low out of
the area, so raised PoPs across southeast Utah.
.LONG TERM (AFTER 00Z SATURDAY)...
Global models are in good agreement in location and strength of
closed low over srn CAL/nrn Baja by 00Z Saturday. The downstream
warm advection wrap around will still clip srn UT through
Saturday. Have leaned toward the higher PoP probability of the EC
as the 700mb convergence and southeast upslope flow into this
portion of the CWA should be enough to set off some showers from
Kanab to Bryce Nat`l Park eastward. Farther west have opted to
lower PoPs as down slope n-s surface gradient should cause air
mass to dry. Breezy to moderately windy conditions expected
Saturday into Monday in the north-south oriented canyons of Dixie.
The remainder of the CWA will finally have a respite from the stormy
weather pattern of late as a ridge builds in across the wrn CONUS
Sunday into early next week. This ridge will create an inversion
beginning Sunday, but it will pale in comparison to the past strong
valley inversion since there is a lack of valley snow cover the air
is of maritime origin vs arctic origin. Have gone with the low end of
The global models differ on the timing of a shortwave disturbance
running out ahead of the westerly flow breaking down the ridge by
Wednesday. The GFS is faster while the EC is about 6-12 hrs slower.
Have gone with an average as the 00Z EC is trending a faster
breakdown of the ridge between the 12Z and 00Z runs and may be
similar in timing to the GFS by the time the next 12Z run rolls
around. This looks like another moist and mild system initially
VFR conditions are expected at the SLC terminal today. However,
there is a 20 percent chance of high end MVFR conditions between
13Z and 18Z in rain and lower CIGS. South winds will generally
prevail but there is a 40 percent chance of winds shifting to the
west between 19 and 00Z. Snow/Rain showers may occur at times this
afternoon but the best threat of snow will be after 02Z.
UT...Winter Storm Warning until 10 PM MST this evening for UTZ006>010.
WY...Winter Storm Warning until 10 PM MST this evening for WYZ021.
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