Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
200 PM PDT sun Apr 19 2015
Synopsis...a weak low pressure system will move southward over the
California coastal waters through midweek. In response...expect
onshore flow to strengthen...a cooling trend to persist...and a
deepening of the marine layer west of the mountains. A secondary low
pressure system will bring a chance of showers to the area mainly
late Wednesday through Friday of this week. A weak ridge of high
pressure will build over Southern California this weekend...bringing
a drying and a slight warming trend.
Discussion...for extreme southwestern California including
Orange... San Diego...western Riverside and southwestern San
Visible satellite continues to show clear skies over Southern
California with a few patchy low clouds out beyond San Clemente
Island. Weak onshore flow persists across the area this afternoon
with coastal to desert surface pressure gradients generally 1 mb
stronger than 24 hours ago.
Through midweek...a weak low pressure system...which currently
resides 200 miles west of San Francisco...will continue to sag
slowly southward off the California coast. This feature will help to
deepen the marine stratus layer...lower temperatures to near or
slightly below average for this time of year...and create gusty
westerly winds in the mountains and deserts. In addition...low
marine stratus clouds will fill the coastal basins during the nights
and mornings...with mostly sunny skies during the afternoons.
A secondary...slightly stronger...low pressure system will drop
south and influence the weather pattern across Southern California
with cooler weather and a chance of showers Wednesday through Friday
of this week. Light rain showers could begin in the san bernadino
mountains as early as Tuesday evening then over areas west of the
mountains and portions of the high deserts by Wednesday afternoon.
Both the 12z GFS and 00z European model (ecmwf) indicate cyclonic flow aloft over our
region through Friday with the main energy from the storm and
highest vorticity maxima passing over northern Baja California. The best
chances for precipitation appears to be on Thursday as the northwest
quadrant of the low passes overhead. The snow level is expected to
range between 6000-6500 feet with a few inches of accumulation
possible over the High Mountain peaks. As the system moves east of
the area on Friday into Saturday...a transient ridge of high
pressure will take its place. This ridge will bring drier weather
along with a slight warming trend through the weekend.
Aviation... 192000z...a few low clouds will linger over the coastal
waters this afternoon...otherwise fair skies and light westerly
winds will prevail from 17z Sunday to 01z Monday. The only exception
will be the northern inland Empire where areas of smoke from the
Highway fire may temporarily reduce visible to 3-5 sm. Low clouds will
return to the coast after 02z Monday with bases in the 900-1500 feet
mean sea level range extending up to 30 miles inland by 14z Monday. Visible
restrictions of 3 sm or less are likely where low clouds intersect
the coastal mesas and inland valleys from 05z-17z Monday. Low clouds
should clear the coast by 18z Monday morning.
Mountains and deserts....few clouds at or above 20000 feet mean sea level and unrestricted
visible through Monday afternoon.
100 PM...no hazardous marine weather is expected through Tuesday.
A storm system moving into Southern California will bring a slight
chance of showers...a northwest swell of 4-6 feet at 10-13 second...and
increasing northwest winds to the coastal waters late Wednesday through
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.