Scientific Forecaster Discussion
fxus66 ksgx 170426
Area forecast discussion
National Weather Service San Diego California
926 PM PDT Wed Aug 16 2017
an upper-level trough will weaken Thursday through Saturday for
minor warming and a shallower marine layer. Another trough will
form off the Southern California coast early next week for cooler
weather and a deeper marine layer.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
patchy low clouds are developing along the coast this evening.
The 00z knkx sounding shows the inversion base has lowered to
around to around 1600 ft, so expect less inland extent of low
clouds tonight. Elsewhere skies were clear. Onshore pressure
gradients have weakened compared to 24 hours ago, so winds in the
mountains and deserts aren't as strong as yesterday.
From previous discussion...
A West Coast trough weakens Thursday through Saturday with
prevailing dry southwest flow aloft and low level onshore flow at
the surface. The marine layer will turn a little shallower as
heights gradually increase, but low clouds will spread into the
coastal zones and western valleys each night. Temperatures will
remain at or slightly below average.
Early next week shortwave energy over the Pacific will drop down the
backside of the trough. This will once again deepen trough along the
West Coast. The GFS and European model (ecmwf) both forecast a 581 dm closed low near
pt Conception on Monday with increasing onshore flow and a deeper
than normal marine layer early next week. Areas along the coast may
have trouble viewing the solar eclipse on Monday due to possible
marine layer clouds.
170425z...coast/valleys...low clouds with bases near 1000-1500 ft
mean sea level and tops around 2000 ft mean sea level will return to the coast and
western valleys 06z, spreading up to 20-25 miles inland
overnight. Expect areas of vis blo 3sm where clouds and terrain
intersect. Low cigs could impact kont and ksbd aft 09z, but
confidence is not high. Clearing to the coast is expected between
16z and 18z Thursday. Low clouds returning late Thursday evening
with slightly lower bases and tops.
Mountains/deserts...clear skies and unrestricted visibility through
no hazardous marine weather is expected through Sunday.
Beaches...a building moderate period south swell, 2-3 ft at 200
degrees, will arrive in the coastal waters late Thursday and
continue through the weekend. This swell may bring elevated surf
of 4-6 ft and strong rip currents to the beaches Friday through
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.