Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
137 PM PDT Sat Aug 29 2015
high pressure aloft will be replaced by a weak low pressure trough
over the next few days. This will result in a cooling trend as
onshore flow increases and the marine layer slowly rebuilds
inland. Marine clouds and fog will develop overnight and move
progressively farther inland through Monday. The clouds and mild
ocean waters will keep overnight minimums elevated over coastal
areas...while cooler nights prevail inland. Overall...temperatures
will run a bit below average inland...while coastal areas average
out slightly above normal through next week.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Satellite imagery early this afternoon showed clear skies over the
County Warning Area...except for a few cumulus clouds over the mountain peaks.
Stratus struggled to form along the coast earlier this morning...but
never did get much of a foothold and the coastal waters remained
mostly clear at midday. Surface pressure gradients continued a 3 mb
onshore trend to the NE and remained about 5 mbs onshore to the
lower deserts. The gradient was supporting isolated wind gusts to
around 30 miles per hour through our Winder desert passes.
A strong ridge remains over the eastpac along 170w...with a weaker
ridge over the Great Plains. A deep low pressure trough covered the
NE Pacific along 135w. This trough will swing inland across the
pacnw through sun...then deepen again along the West Coast as cold
air reinforcements slide in from the north. The trough will dominate
the weather over California through next week...maintaining onshore flow and
a moderately deep marine layer. This pattern will also inhibit any
monsoonal flow into the region through at least Labor Day.
Expect near...to cooler than average days...and near...to warmer
than average nights to prevail west of the mountains next week. No
precipitation is expected.
Aviation... 291937z...coast/valleys...unrestricted visible and sky clear
through 30/0300 UTC. 30/0300-1500 UTC...patchy stratus gradually
developing 10-15 sm inland...with bases 800-1100 feet mean sea level and tops
around 1500 feet mean sea level. Expect areas of 2-5 sm visible and local visible at or below 1
sm along higher coastal terrain and inland mesas. Marine layer
inversion strength around 7 degree c. For ksan and kcrq
sites...forecast confidence in occurrence is moderate...with low-to-
moderate confidence for ksna. Clearing of stratus 30/1500-1700 UTC.
Mountains/deserts...after 30/0000 UTC...SW to west winds 20-25 knots with
gusts 35-45 knots along mountain ridges...through/below canyons and
passes...along the Desert Mountain slopes and into the adjacent desert
foothills will create moderate-strong uddfs and low level wind shear over and east of the
mountains winds will gradually weaken early Sunday morning.
Otherwise...unrestricted visible sky clear through Sunday morning...except for
scattered cumulus over the mountain ridges and desert slopes through 30/0200
UTC with bases around 10000 feet mean sea level.
Marine... 1237 PM...northwest winds gusting to 25 knots over portions
of the outer coastal waters this evening and again Sunday afternoon
and evening will result in conditions hazardous to small craft. A
Small Craft Advisory has been issued. Winds and seas will improve by
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
Pz...Small Craft Advisory from 5 PM this afternoon to 2 am PDT Monday
for waters from San Mateo Point to the Mexican border
extending 30 to 60 nm out including San Clemente Island.