Scientific Forecaster Discussion
fxus65 kslc 271240 cca
Area forecast discussion
National Weather Service Salt Lake City Utah
540 am MST Mon Feb 27 2017
Synopsis...the next cold Pacific storm system will impact much of
the area through at least Tuesday evening. An increasingly dry and
mild westerly flow aloft will set up for the latter half of the
Short term (through 12z thursday)...the axis of the approaching
upper trough currently extends across the northern Sierra Nevada
through eastern Oregon. The 700mb baroclinic zone is draped over
northwest Utah per the latest rap analysis, near where a band of
snow currently exists. The boundary will continue to strengthen
through this afternoon as it slowly moves south into central Utah,
with snow filling in along and behind it while gusty southerly winds
will be common across southern Utah ahead of it. With frontogenesis
being strongest across central Utah, the heaviest snow is expected
across Utah County through west-central Utah and the adjacent
mountains later this morning through this afternoon.
Southern Utah may see some light precipitation in the prefrontal
environment through around midafternoon, but the bulk of
precipitation there will occur late this afternoon through the
overnight hours as a plume of moisture arrives from the southwest,
combining with the cold front which will be crossing the area during
that time. Overall, much of the forecast area will see accumulating
snow, with the greatest amounts across central Utah as previously
mentioned. Going winter weather highlights will continue, although
the southern Utah zones probably could have been fine with a later
start time given the greatest impacts will be during the latter part
of the day.
There may be a brief lull in the weather late tonight into early
tomorrow morning as the initial shortwave trough exits the area and
a second disturbance, which is currently located off the British
Columbia coast, approaches Utah. This trough will cross the area
Tuesday afternoon which will bring snow showers back to the portions
of northern and central Utah. A cold and moist northwesterly flow
will keep lingering showers in place through Tuesday night. Warm
advection at 700mb will then develop for Wednesday, keeping some
clouds in place across northern Utah with a few snow showers
possible across the far north.
Long term (after 12z thursday)...high pressure over the forecast
area is expected to weaken some Thursday night into early Friday as
a weak wave grazes northern Utah and southwest Wyoming. Moisture
looks limited so associated precip should be as well, but it looks
to sag a weak frontal boundary into northern Utah.
Behind this wave, ec/GFS shows a more zonal flow developing over the
state for the first part of the upcoming weekend with moisture
increasing over northern Utah in weak warm advection. This will
allow for a chance of precip, with a couple of weak shortwaves
Global models both show another grazing system for the latter half
of the weekend into day seven, but the latest GFS is 12-18 hours
slower bringing the system in compared to the ec. All guidance shows
a good amount of cold air moving into northern Utah with the
boundary with some decent dynamics but very limited moisture, so
have kept pops low at this time.
Aviation...at the slc terminal...prevailing IFR/LIFR in snow is
expected through the early afternoon hours. Occasional snow is then
expected to linger through much of the afternoon before diminishing
during the late afternoon/early evening. Northwest winds are
expected throughout the day.
Utah...Winter Weather Advisory until 4 am MST Tuesday for utz001>003-
Winter Storm Warning until 4 am MST Tuesday for utz004-008>010-
Wyoming...Winter Weather Advisory until 4 am MST Tuesday for wyz021.
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