Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
414 PM MST Thursday Nov 26 2015
Synopsis...a cold upper level low pressure system will remain
over the Great Basin through the remainder of the Thanksgiving
Holiday weekend. High pressure aloft will settle into the region
early next week.
Short term (through 00z monday)...the cold core upper low still
positioned along the Utah/Nevada near kely will begin a westward
migration through Nevada Friday. This upper low will then turn
back to the east Friday night...then track east-northeast across
northern Utah this weekend.
Strong canyons winds along the Wasatch front/Cache Valley are the
main concern in the short term forecast tonight/early Friday.
Light east-southeast winds near 700mb wind earlier today have
strengthened and become a consolidated easterly flow across the
far north this afternoon. Cold advection easterly flow into the
northern Wasatch Range and a 10+ mb pressure gradient between
northern Utah/western Wyoming will support Strong Canyon winds
across the northern Wasatch front/Cache Valley tonight through
Friday morning. Peak gusts expected in this event likely to fall
in the high end of the advisory category...so will leave the
current Wind Advisory in place in the afternoon forecast package.
Considered extending the advisory into the Salt Lake Valley...but
will hold for now as any strong gusts probably will remain just
below advisory criteria.
Friday looks to be the least active day precipitation-wise as the upper
low center settles into western Nevada. Weak dynamic/thermal
support for lift with the low so far remove should limit precipitation to
loosely organized showers during the day. Conditions favorable
for precipitation will return by Friday night as the upper low turns back
to the east through Nevada. Increasing dynamic lift and thermal
advection ahead of the advancing upper low will result in
increasing areal coverage of precipitation across southern/eastern Utah
Precipitation will shift into the north Saturday as the low center moves
into western Utah. Drier air along the southern flank of the low
should bring a fairly quick end to most precipitation down south...with
the bulk of the precipitation in the northeast flank of the advancing
low over Central/Northeast Utah and southwest Wyoming.
As the upper moves northeast into western Wyoming Sunday the
trailing cyclonic northerly flow could generate one final burst
of snow along the urban corridor and adjacent Wasatch mountains
beginning Sunday afternoon. This event could hit a peak during the
late afternoon...and possibly continue beyond the short term
Long term (after 00z monday)...the GFS and ec are in better
agreement at the beginning of this period with both showing a
somewhat elongated low from western Wyoming into northern Utah. This
will bring the coldest air associated with the low across the County Warning Area
Sunday night into Monday along with weak dynamics and moisture
resulting in a chance of snow across the northern portion of the
County Warning Area.
From Monday night through the end of the extended have gone with a
dry forecast as the models show a ridge of varying strengths
developing over the Great Basin. The GFS shows a weak trough trying
to work its way into the northwest portion of the County Warning Area by Thursday
but the trend has been to get weaker with each successive run.
Therefore have leaned toward the ec which does not depict this
Temperatures will be slow to climb in the valleys as a strong
inversion likely to be in place. By Thursday the temperatures get a boost
across the western valley as the ec shows a trough approaching the
Aviation...the main forecast challenge at the slc terminal through
this taf period will be winds. Although the surface gradient argues
for northerly winds...gusty east winds blowing out of canyons in the
Wasatch are causing winds at the ASOS to be east southeast while
Midfield winds are northerly. This dichotomy is expected into this
evening before likely becoming northerly across the entire airfield.
Utah...Wind Advisory until noon MST Friday for utz001-002.
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