Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
438 am MST Thursday Dec 5 2013
Synopsis...the forecast area will remain under a very cold upper
level trough through the end of week. The next cold Canadian storm
system will impact the area over the weekend.
Short term (through 00z monday)...a very cold upper trough
encompasses the western Continental U.S. Early this morning...and will remain
in place through the upcoming weekend. With the exception of
northwest Utah where a stratus deck currenty resides...skies have
cleared out across most of the forecast area overnight...and with
fresh snowcover temperatures have plummeted particularly across
central and southwest Utah...with numerous locations falling below
This cold airmass has also allowed weak lake effect convection to
develop over the gsl...however very light winds have kept this
activity confined over the water. As the day progresses...and a
weak shortwave currently crossing northeast Nevada crosses the
area...this activity may spread off the lake and into portions of
the Wasatch front. Have maintained slight chance wording for this
activity. Otherwise this trough does not have much moisture to
work with...but may be able to initiate show showers primarily
over the higher terrain of northern Utah.
A shortwave trough currently digging south along the British
Columbia coastline is forecast to swing through the Great Basin
late Friday then through the forecast area during the upcoming
weekend. Ahead of this wave warm advection aloft will commence
during teh day Friday across northern Utah bringing an increase in
cloud cover and perhaps some light snow to the higher terrain.
The 00/06z models have trended more favorable in terms of snow
potential across much of the forecast area from roughly Ogden
southward beginning late satudray morning...and continuing
through Saturday night. Given the very cold airmass in
place...snowfall will accumulate quickly on all surfaces from the
onset. As it stands now...this system has the potential to put
down several inches of snow across most valleys...with
accumulating snow also possible in utahs Dixie. Have raised probability of precipitation
considerably across the forecast area for satudray through
Saturday night...with snow tapering off Sunday.
Long term (after 00z monday)...the weekend trough looks to exit the
region Sunday night into Monday. Despite warm advection aloft...
temperatures Monday morning are likely to be quite cold after skies
clear in most locations.
Stable northwesterly flow looks to develop for Monday and
Tuesday...as a broad trough lingers over the Midwest. Some slow
warming should occur during this period...but most valley locations
will likely remain cold and inverted for the beginning of the week.
The GFS and European model (ecmwf) begin to diverge a bit starting Tuesday
night...but both indicate the possibility of another storm moving
into the Great Basin on Thursday. The European model (ecmwf) has the sharper trough
solution...with strong warm advection and increasing west-
southwesterly flow ahead of the system. If the European model (ecmwf)
verifies...improved mixing could be on tap for Wednesday and
Thursday. Current forecast for these days leans toward this less
inverted solution...though have kept temperatures somewhat conservative
given uncertainty this far out and likely snow cover still in place.
Aviation...surface winds at the slc terminal are expected to switch
to the northwest between 16z and 19z...but speeds should generally
remain 7 knots or below. There is a 70 percent chance of ceilings
below 7000ft developing before 00z Friday. There is also a slight
chance of brief MVFR or IFR conditions in light snow showers
today...but little to no accumulation is expected.
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)