Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
427 am MST Monday Dec 9 2013
Synopsis...the weather disturbance that crossed northern Utah
overnight will continue southeast out of the state later this
morning. High pressure aloft off the West Coast will maintain a
stable and increasingly dry northwest flow across the Great Basin
Short term (through 00z thursday)...the upper trough that moved
into northern Utah during the evening has shifted into northeast
through central Utah early this morning. This trough will move
quickly off to the southeast...and should be out of the state by
late this morning.
Snow has been ending quickly in the subsidence behind the the
passing trough overnight. The exception remain areas southeast of
the gsl where instability extending up to around 700-650mb is
supporting lake-enhanced snows across the Salt Lake...Tooele and
northern Utah valleys. This activity should persist through the
early morning hours...so will maintain the Winter Weather Advisory
for minimal additional accumulation but significant impacts for
the morning commute.
The high-amplitude upper ridge over the eastern Pacific will
maintain a stable and mostly dry northwest flow across the Great
Basin through midweek. Cloud cover...or the lack thereof...will
have a substantial impact on temperatures the next couple of days. If
skies clear tonight...then valleys temperatures could end quite cold
Tuesday morning. Add to this fairly rapid warming aloft and the
expected valley inversions could be quite strong for several days
to come. Fog and urban haze will become more of an issue with
time...though with the fog it may be a bit slower to develop and
spread out due to the extremely cold temperatures and gradual drying.
Long term (after 00z thursday)...ridge axis is prognosticated to move
overhead by Thursday afternoon...further increasing stability over
the area. This will keep valley inversions strong while 700 mb temperatures
around -1c to 0c would result in mild temperatures at higher elevations. As
the ridge axis moves overhead...global models show a Pacific storm
system moving across Arizona Thursday through Friday morning. This
system likely remains too far south for precipitation over southern
Utah...but could cause some increase in cloud cover.
Ec/GFS continue to indicate a weak storm system will move across
Utah Friday through early Saturday. 700 mb temperatures look to drop to the
-8c to -10c range with the system...and increasing flow aloft might
be enough to provide at least partial mixing of valley inversions.
Because of this...have indicated modest warming of valley temperatures for
the weekend. Moisture looks to be a bit limited with the system at
this time...but would likely be enough to produce some snow...at
least over the higher terrain. Have kept some mountain probability of precipitation in
during this time.
Northwest flow is expected to build back over the forecast area
behind the exiting trough. Models have backed off on the trough for
Sunday/Monday...with the European model (ecmwf) showing a grazing system that might
bring some clouds into northern Utah while the GFS indicates a
system even weaker than that.
Aviation...VFR conditions are expected through the day at the slc
terminal. Ceilings at or below 6000 feet are expected to prevail during
the early morning...becoming more scattered between 14z and 16z.
There is a 30 percent chance of brief low-end MVFR to high-end IFR
conditions in snow showers through about 15z. Northwest winds are
expected throughout the day but there is a 30 percent chance of
light and variable or light southeasterly winds during the morning.
Utah...Winter Weather Advisory until 9 am MST this morning for utz003.
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)