Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
352 PM MST Sat Dec 7 2013
Synopsis...the cold winter storm system centered over the
Great Basin will track east across Utah through tonight.
Widespread snow through Sunday will be followed by very cold
temperatures heading into the first half of next week.
Short term (through 00z tuesday)...
water vapor loop shows our next system approaching from the Pacific
northwest and western Great Basin. Acars 400-250mb wind observations
place a northwesterly 125-150kt jet along the West Coast.
GOES/GPS/rap/12z radiosonde observation indicate the precipitable water value is
between 0.05" and 0.25".
Any snow will likely quickly turn into a significant travel impact
with Road temperatures being quite cold.
Winter storm will transition in nature early this evening as the
cold front arrives from the northwest. With 850-700mb flow switching
from south to west...then northwest...expect snow coverage and
intensity to increase along the Wasatch front this evening.
Meanwhile ahead of this boundary across south central and southeast
Utah...high resolution guidance suggets soutwest wind gusts to be in
the 45-55 miles per hour range. This coincides with 700mb flow increasing to 50-
While the frontal band will shift southeast overnight...a second
round is forecast to get going over the north due to the combination
of the passage of the middle level trough and the threat of lake effect
snow. The trough passage is expected to actually encrourage lake
effect due to dynamical lift and spreading of higher relative humidity in the lower
levels. Right now the lake band is expected to impact Salt Lake
County...but will all lake bands...the iniitiation point and
downstream trajectory can be tricky to Pin Point.
Gusty northwest downslope flow across the raft rivers...western
Uinta Basin...and Castle country will contribute to areas of blowing
snow later tonight.
Areal extent of precipitation rapidly decreases late tonight with
the passage of the middle level trough. Counting on lake and
oragraphics to keep local precipitation processes going
Sunday...through not expecting a lot in the way of instability
mountain showers due to being in between two troughs and lack of
instability seen on the sref.
Secondary wave moves overhead late Monday night...potentially
leading to another round of showers...and potentially allowing re-
development of lake effect snow. Otherwise quite cold with fresh
snowpack and lack of widepread cloud cover in place.
Trough axis passes Monday with precipitation ending quickly.
Pressure graident will support locally gusty winds in downslope
Long term (after 00z tuesday)...
cold northwest flow will remain across the region early Tuesday
but warming temperatures will occur through the afternoon. Stable
cold conditions will get locked in the valleys for most of the
week. The only chance of for some snow showers will be across the
extreme north Tuesday night into Wednesday as a weak disturbance
moves through in northwest flow. A strong ridge is forecast to
move overhead Thursday and Friday which will allow temperatures to
warm rapidly across the higher elevations but most of the valleys
are expected to remain trapped under an inversion...especially the
Uinta Basin and western valleys where snow cover is extensive.
Confidence is low on another disturbance brushing by the northern
half of the County Warning Area come Saturday as the GFS shows a shortwave but the
ec does not.
Aviation...ceilings are expected to remain between 2500 and 3500 feet
above ground level at the slc terminal through 23-01z...after which ceilings should
lower as the main trough axis moves across and the winds aloft shift
to northwest. IFR conditions are expected between 01z and 04z with a
30 percent chance of intermittent MVFR conditions. Snow
accumulations of 2 to 4 inches are expected on untreated surfaces
through 06z tonight with additional snow after 06z. Surface winds
should shift to northwest between 23 and 24z.
Utah...Winter Storm Warning until 10 am MST Sunday for utz011>013-
Winter Storm Warning until 6 PM MST Sunday for utz002>004-
Winter Storm Warning until noon MST Sunday for utz001-005-
Wyoming...Winter Storm Warning until 6 PM MST Sunday for wyz021.
For more information from National oceanic and atmospheric administration/S National Weather Service visit...
http://weather.Gov/saltlakecity (all lower case)
For frequently asked questions about the area forecast discussion
http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)