Scientific Forecaster Discussion
fxus66 ksgx 232009
Area forecast discussion
National Weather Service San Diego California
105 PM PDT Tuesday may 23 2017
high pressure aloft will drift east tonight and a weak trough moving
in from the west will bring cooling Wednesday through Friday. Low
clouds will spread farther inland each day as the marine layer
deepens. There may be areas of light rain west of the mountains
Thursday night into Friday morning. Windy in the mountains and
deserts. High pressure will rebuild over the west this weekend for
warmer weather and a shallower marine layer.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Cool marine air and low clouds surged rapidly inland across the
coastal zones between 10 am and noon today. A steep thermal
gradients was a primary factor in generating the strong onshore push
and the gusty westerly winds. At noon the temperature at Palm
Springs was 108, and 66 at North Island and Oceanside. That's a 42
degree temperature gradient from the coast to the desert. The
temperature at Rancho Bernardo topped out at 81 degrees at 10:43 am,
then fell to 70 degrees at 11:50 am.
It was hot in the valleys and deserts today, but tomorrow won't be
quite as hot as the 588 dm ridge over California moves east and
takes the heat bubble with it. Sixty meter height falls over so-cal
will translate into 5 to 10 degrees of cooling tomorrow in the
valleys and deserts. Lower heights will allow the marine layer to
deepen, and low clouds/fog will spread into the inland valleys by
A weak shortwave ejecting from the parent trough over the Pacific
will track northeast across Santa Barbara/venture/la counties
tomorrow afternoon. This feature may have enough elevated cape and
instability for isolated high-based convection over the San Gabriel
Mountains. The track of the upper low is a little too far east for a
significant chance over the sbd mountains, but there may be
afternoon cumulus in that area tomorrow. 850 mb wind increase to 30-40 kt
tomorrow evening, and it will turn windier in the mountains and
Thursday and friday: the parent trough over the Pacific slowly moves
inland across socal and it will turn noticeably cooler in the
valleys, mountains and deserts. High temperatures will be several
degrees below average both days. Windy in the mountains and deserts
with gusts of 30-40 mph in the afternoons and evenings with gusts of
50-55 mph in the wind prone areas. The marine layer will deepen to
around 5000 feet Friday morning, and this deep moist layer combined
with a weak shortwave aloft will likely produce areas of light
rain/drizzle west of the mountains Thursday night/Friday morning.
Saturday through monday: the trough slides east Friday night with
weak high pressure rebuilding aloft along the West Coast for warm,
dry weather through the Holiday weekend. A shallow marine layer and
weak onshore flow will keep coastal areas cooler.
232000z...low clouds have begun to move ashore this afternoon and
will again spread inland this evening after 04z. These clouds will
be based at about 800-1000 feet msl and spread 15-20 miles inland by
12z Wed. Vis will be reduced to 1-3sm or lower where clouds and
terrain intersect. Otherwise, mostly clear skies except for a few
high clouds and afternoon cumulus over the mountains.
no hazardous marine weather is expected through Saturday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.