Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
354 PM MST Thursday Dec 12 2013
Synopsis...a weak weather disturbance will cross the eastern
Great Basin on Friday. A dry northwest flow will follow for the
weekend into early next week...maintaining a stable airmass across
Short term (through 00z monday)...strong valley inversions
prevail across the forecast area this afternoon...and this will
likely remain the case through the weekend and beyond. The result
will be a continued decrease in air quality...and an increasing
chance of fog.
A weak shortwave trough currently along the Pacific coast will
cross the forecast area during the day Friday. This feature will
be weakening as it crosses the forecast area...thus aside from an
increase in middle and high level cloud cover little if any
precipitation is expected even across the higher terrain.
Modest cooling aloft with this feature will likely be
insufficient to have much if any effect on valley
inversions...with the possible exception of The Castle country
area where downslope winds may help temporarily erode the stable
surface layer. As such have maintained haze in the forecast along
with little in the way of temperature changes from day to day
across the valleys.
Long term (after 00z monday)...strong ridge over California Monday
will gradually move overhead late Tuesday and Tuesday night. This
will provide a dry and warming flow across the region. Temperatures
at 700 mb will rise from 0 to 2c early Monday to 4 to 6c Tuesday
afternoon. High elevation locations above about 6000-7000 feet will
experience this warm up but unfortunately with very light winds this
warm up will not be felt in the valleys where a strong inversion
will continue to be in place...except in the Dixie where the
inversion should break. A weak trough will cool temperatures across
the higher elevations Wednesday while little if any change will
occur in the valleys.
After midweek...the ec latches onto a significant cold trough that
it moves whole heartedly through Utah Thursday with a continued
somewhat moist northwest flow with additional disturbances Friday
into Saturday. If the ec is correct...this storm will be strong
enough to overturn the inversion and bring snow back into the area.
However...the operational GFS forecast is not onboard with this
trough on Thursday but it does have a trough coming in on Friday.
Have leaned toward the ec as a few of the GFS ensemble members are
more similar to the ec. The naefs probability of quantitative precipitation forecast greater than
0.01 of an inch is about 20-40 percent Thursday across the northern
half of Utah which supports the slightly greater than climatology probability of precipitation in
the Thursday and Thursday night time frame.
Aviation...at the slc terminal...VFR conditions are expected into
this evening. However...there is a 40 percent chance of MVFR
visibilities after about 04-05z. There is a 10 percent chance that
IFR visibilities could develop across the western runway after 08z
and periodically impact other portions of the terminal. Light
northwest winds will prevail until about 04z and then are expected
to shift to the southeast or be calm.
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)