Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 231640
Area Forecast Discussion
National Weather Service Salt Lake City UT
1040 AM MDT Thu Mar 23 2017
.SYNOPSIS...A Pacific storm system will continue to move east across
the Great Basin today. High pressure will return for Friday,
followed by another storm system this weekend.
.DISCUSSION...Morning water vapor and H5 analysis indicate the mid
level circulation of the upper trough has shifted east over
south-central Utah, with a cyclonically oriented upper jet lifting
northeast over the 4-corners region. Strong mid level convergence
continues to exist along the northwestern flank of this low aiding
tight near H7 thermal packing within a near stationary axis, this
driving moderate to at times heavy precip along the bulk of the
I-15 corridor from the northern Wasatch Front south through
central Utah. KSLC has thus far recieved 1.25" rainfall setting a
new record for the day, and will likely push for another quarter
of an inch of rain today.
Anticipating a more transitory period to develop through this
afternoon as the upper low continues to shift east and downstream
of the area. The aforementioned axis will shift east-southeast
coincident allowing mid level cold advection to settle in across
the area. With this, anticipating precip to remain focused along
the I-15 corridor (and bordering terrain),likely becoming more
orographic in time through the peak heating hours this afternoon.
Snow levels have been highly dependent on PI rates (as low as
4800ft in the north) over the last several hours, but should in
large settle to near 6000ft this afternoon. Winter Weather
Advisories remain in effect for the mountains with snowfall
continuing at times into this evening, but not anticipating much
if any impact to roadways this afternoon, thus thinking the late
morning expiration is justified. Will reassess over the next hour.
A more rapid downstream translation of the trough late today into
the overnight will allow precip to taper off W-E by nightfall.
Only made minor updates this morning, primarily to tweak QPF/Snow
and raise PoPs beneath the near stationary axis.
PREVIOUS DISCUSSION...A shortwave ridge will briefly build into the
area tomorrow, resulting in warmer and drier conditions. However,
another trough will be crossing the West Coast tomorrow and will
continue through Utah late tomorrow night through Saturday.
Widespread precipitation can be expected once again with this
storm with snow levels falling to near 6000ft. This will be a
faster-moving system and storm totals will not be as large as this
current storm, but brief heavy precipitation can be expected.
The active weather pattern looks to continue through the long
term period, though the latter half of the weekend begins with
high pressure over the forecast area. This ridge shifts east
Monday ahead of the next approaching Pacific storm system, which
consolidates into a closed low before tracking along the UT/AZ
border beginning Monday night. EC is a bit faster with this storm,
moving it through the Four Corners by Tuesday night. In the
latest GFS, the system drifts over Arizona through Wednesday
before tracking east of the area Wednesday night/Thursday morning.
Regardless, both models bring another round of solid precip to
the entire forecast area as the system passes.
Brief ridging is expected early Thursday in between systems, but
models are in good agreement that a colder Pacific Northwest system
moves through beginning Thursday, likely remaining over the area
well past day seven. Have bumped up POPs at the end of the forecast
period to account for this system.
.AVIATION...VFR conditions are expected to prevail at the SLC
terminal this morning, but there will be periods of MVFR conditions
in heavier rain, primarily through 20Z. South winds should switch to
northwest by 18z. Cigs expected to lift above 7000 feet between 19z
and 22z as showers diminish near the SLC terminal and remain mostly
confined to the higher terrain to the east and south of the TAF site.
UT...Winter Weather Advisory until 11 AM MDT this morning for
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