Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
940 PM PDT Sat Sep 20 2014
the upper low that hung out along the central California coast on Saturday
will depart to our north and east on Sunday. This will result in
earlier clearing of the low clouds and an increase of 1 to 3
degrees in the high temperatures for Sunday. A building ridge of
high pressure will bring a warming trend for the first half of the
workweek...with above average temperatures arriving by Tuesday and
Wednesday. Low pressure moves inland along the northern California
and Oregon coasts Thursday and Friday...bringing dry and cooler
weather to Southern California.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Water vapor imagery this evening shows a high amplitude ridge over
the western US...with an embedded cutoff upper low along the central
California coast inducing thunderstorms over the Great Basin and sierras. A
lack of moisture limited southwest California to only a few vertically
challenged cumulus over the higher peaks and upper deserts today.
West of the mountains temperatures were 1 to 3 degrees cooler than
yesterday...due to a stubborn deck of marine stratus.
Through Sunday evening...low stratus deck will redevelop from the
coast to the western slopes of the mountains overnight...with areas
of patchy fog between 1500 and 2500 feet. The shifting of the trough
axis to the northeast and drying in the middle-levels will bring lower
marine layer tops and a thinner stratus deck tonight. As a
result...clearing should be quicker on Sunday.
The upper low currently over the central California coast will slowly
transition to and open wave embedded in the broader flow during the
day on Sunday. In response...500 mb heights will begin to slowly
increase over the region. When combined with quicker clearing
times...this will add a couple of degrees to mainly inland high
temperatures on Sunday.
Monday through Wednesday...a transitory ridge will slowly amplify
over southwest California...as a trough digs off coast of the Pacific
northwest. As a result...high temperatures will trend
upward...returning to 3 to 6 degrees above average by Wednesday. A
slow decrease in the coverage and depth of the marine layer can be
expected though Wednesday morning...with 500 mb heights increasing
to around 591 dm.
Thursday though Saturday...a broad trough with several embedded
shortwaves will push inland along the West Coast. Onshore flow and
height falls will bring cooler weather to our region with locally
gusty winds through the passes and along the desert slopes. The
European model (ecmwf) and GFS have come into better agreement on the amplitude of
the trough compared to this time yesterday...but continue to
disagree on the rate of eastward propagation. Have trended the later
forecast periods toward the GFS solution given slightly better run
to run constancy.
210330z...coasts/valleys...stratus will develop slowly this
evening...mainly reaching coastal airports between 06z and 09z.
Bases will be 1500-2000 feet mean sea level with tops to 2500 feet mean sea level. By
12z...stratus will spread 25-30 Michigan inland...including west and south
parts of the inland Empire. Most visible will remain above 5 Michigan...though
higher terrain will be locally obscured. Clearing will occur in most
areas between 16z and 18z Sunday. Stratus will redevelop Sunday
evening with slightly lower bases.
Mountains/deserts...mostly clear with unrestricted visibility
through Sunday night.
830 PM...no hazardous marine weather is expected through Thursday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.