Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
907 PM MST Friday Nov 27 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 (until 00z tuesday)...the vorticity maximum lifting north
through east-central Utah appears to be based on water vapor
animation becoming better organized this evening. Deep and
steadily increasing lift as evidenced by cold top cooling and
widespread radar return over eastern Utah/western Colorado exists
in the north and east flanks of advancing vorticity maximum. Deep
layer and moisture warm advection will drive precipitation generation and
intensification as the maximum heads into southwest Wyoming overnight.
Have updated the afternoon forecast to increase probability of precipitation and the
expected snowfall accumulations in the Uinta Mountains and across
extreme southwest Wyoming tonight through early Saturday morning.
The above mentioned dynamic feature will likely turn back to the
west and track across northern Utah Saturday. Light snow will
likely develop along the northern/central portions of the urban
corridor near the vorticity maximum Saturday morning. Moist warm
advection will still exist ahead of this features to the west and
south of the maximum...leading to an increase in precipitation across
northwest through west-central Utah during the afternoon. The 00z
GFS representation of the precipitation looks best with this at first
glance this evening.
Canyon winds remain an issue along the northern/central Wasatch
front this evening. This evening event is much more localized to
the wind prone areas south of I-84 through Davis County. The
surface pressure gradient has relaxed from 10+ mb to around
5-7mb between central Wyoming and the Wasatch front. Supporting
cold advection easterlies will persist through late tonight...
then turn more northerly Saturday morning.
The migration of the broad upper low over the Great Basin to the
east of Utah late in the weekend will shift the emphasis for snow
to northern Utah. A moist and cyclonic northwest flow on the back
side of the exiting upper low will bring light to moderate snow to
the urban corridor and the adjacent mountains Sunday morning the
best chance for snow will exist Sunday afternoon/evening...then
taper off to just light mountain snows late Sunday night/early
Monday. High pressure aloft working into the state from the west
will likely bring an end to any lingering showers by late Monday
Previous long term (after 00z tuesday)...continued downstream
progression of the closed low will allow for rapidly building
heights and onset of a notable warming trend aloft beginning
Tuesday. The short wave ridge responsible for this will begin to
amplify over western Nevada at that time then gradually spread
overhead Wednesday into Thursday further stabilizing the airmass
in place. Maintaining a dry forecast through Thursday night as
Ample warming aloft /h7 temperatures trending from roughly -12c 00z Tuesday
to near 0c come 00z Thursday/ will likely aid in developing
relatively Stout inversions across the valleys and basins across the
state...especially those retaining at least some snow cover. This
makes valley temperatures especially challenging in the forecast and will
have to monitor trends and details regarding cloud cover through
early week to better handle just how much warming will be realized.
Will also have to monitor the potential of building haze through the
Globals beginning to key in on the next potential trough Friday into
the weekend. All signs point to another hard split...with most
likely scenario at this time forming yet another closed low over the Desert
Southwest. Will continue to monitor...but feel guidance such as the
European model (ecmwf) with its slower progression and more western split will
continue to be the way to lean unless proven otherwise.
Aviation...clouds will increase from the east late this evening
with brief periods of light snow possible after 06z. Ceilings
initially near 9k feet will gradually lower to between 5k and 6k feet
after 11z. Ceilings/visibilities may briefly lower further during
light snow events...but likely remain in the VFR category. Canyons
winds along the East Bench will maintain east-southeast winds at
the terminal through Saturday morning. Brief periods of light
west-northwest winds are possible during the strongest canyon
winds through around 15z.
Utah...Wind Advisory until 9 am MST Saturday for utz002.
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