Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
1051 am MST Thursday Nov 26 2015
Synopsis...a cold upper low will meander around the Great Basin
through the Thanksgiving weekend.
Discussion...morning analysis places a vertically stack low to
middle-level circulation center near the Nevada border south of
Wendover with a strengthening shear axis above evident in water
vapor imagery from central Nevada extending into extreme southeast
Montana. Light snow will continue underneath the shear axis along
the northern flank of the middle-level circulation near the border
with Idaho and Nevada border through this afternoon. Also looking
at an area of organized light snow continuing over the central and
northeast mountains associated with a vorticity maximum rotating
northeast around the main upper low today.
Veering near 700mb winds beginning late this afternoon will create
a cold advection easterly flow across far northern Utah tonight
through Friday morning. Have discounted the 12z NAM solution as it
weakens the near 700 mb flow overnight and maintains the cold
advection well back into southwest Wyoming. Will follow the 12z
GFS solution with its fairly strong near 700mb cold advection
spilling into the far northern Utah tonight. Strong canyons winds
look to be a given across the Cache Valley/northern Wasatch
front...with a lesser event for the Salt Lake Valley.
Question becomes will this turn into a downslope high wind event
for the northern Wasatch front/Cache Valley. The latest GFS has
brought significantly strong cold advection farther south and west
into the back side of the northern Wasatch Range with a solid
25-30 kts cross barrier flow tonight through early Friday. This
still looks to be primarily a canyon wind event...though the
trends has moved towards a downslope event for the above mentioned
zones. Will maintain the current Wind Advisory for canyon winds...
though if the 18z guidance continues the upward trend will have to
consider boosting this to a warning.
The veering flow may also bring an increase in snow across
northeast Utah tonight. Increasingly moist low-level warm
advection as the flow aloft veers could lead to increased
snowfall along favorably oriented terrain in the northeast
On Friday the center of the upper low will migrate back to the
west into western Nevada. This repositioning of the low center
will leave Utah open to vorticity maxes rotating north through the
state Friday through Friday night. Periods of organized snow
likely during that time...though heavy snows are not anticipated.
The upper low will again turn back towards Utah Friday night...
tracking northeast through western/northern Utah Saturday through
Saturday night. An expanding area of snow will likely form in the
northern/eastern flanks of the low as it moves through region.
Snow should persist across northern Utah late in the weekend...
then gradually decrease as high pressure aloft moves east across
the Great Basin early next week.
Aviation...light and variable winds are expected at the slc
terminal through this morning but should be northwest this
afternoon. Few to scattered clouds this morning but likely to
fill in and become broken later this afternoon. There is a 40
percent chance that ceilings end up lower than 7k feet above ground level after
Utah...Wind Advisory from 6 PM this evening to noon MST Friday for
Wyoming...Winter Weather Advisory until noon MST today for wyz021.
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For frequently asked questions about the area forecast discussion
http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)