Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
926 PM PST Thursday Dec 12 2013
areas of low clouds and fog will likely move into the coastal
areas late tonight then burn off Friday morning...giving way to
mostly sunny skies. Expect daytime temperatures a few degrees
lower than they were today. Dry and warmer with locally strong and
gusty offshore winds for this weekend and early next week. The
offshore winds will be strongest Saturday and Sunday
mornings...weakening by Monday. However...warm and dry conditions
with offshore flow will continue into Tuesday. A gradual cooling
trend will then develop for Wednesday and Thursday...with onshore
flow and coastal low clouds returning.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Satellite imagery shows the upper low accelerating as it moves NE
across Arizona...taking the scattered showers with it. Surface pressure
gradients continue to trend onshore with +2.6 mb san-ipl.
This upper level low will continue to move NE over the next 24
hours. The shortwave trough moving into the Pacific northwest
will continue to break down the upper ridge as it moves southeast across
northern California and into the Desert Southwest during the day
on Friday. The high resolution models are showing the marine layer
redeveloping tonight as the surface flow turns onshore in response to
the approaching trough. Expect slightly cooler conditions to
prevail through Friday...with locally gusty onshore winds
developing across the mountains and deserts.
For Sat and sun...a high pressure ridge rebuilds over California
as the trough moves east...and a surface high moves into the Great
Basin. This will bring dry and warmer conditions with strong and
gusty offshore winds. The NE to east winds will be strongest in and
below canyons and passes...over the coastal slopes and portions of
the inland valleys. The winds will strengthen late Friday night and
continue through Sunday...weakening Sunday afternoon. Numerical
models indicate the potential for wind speeds of 20-30 miles per hour with
gusts 40-50 miles per hour. Local gusts to 60 miles per hour are possible in the wind
prone locations. Daytime temperatures will reach the 70s west of the mountains
on Sat and approach 80 degrees in some inland valley locations on
For Monday and Tuesday...the upper ridge remains in place through
Tuesday...keeping conditions dry and relatively warm with daytime
temperatures in the 70s to near 80 degrees west of the mountains the surface high
over the Great Basin will weaken and move east...resulting in
less of an offshore pressure gradient and decreasing winds.
For Wednesday and Thursday...the upper ridge weakens and shifts east in
response to a trough approaching from the northwest. This will likely
bring a return of onshore flow...and coastal low clouds and fog
during the nights and mornings.
130400z...coast...patchy stratus...with bases around 900 feet mean sea level and
tops near 1500 feet mean sea level...will develop around 5sm inland by middle Friday
morning. Stratus may move inland and back offshore at times
overnight. Visible of 1-3sm br is expected where stratus nears higher
terrain...with some areas of 1/2sm fog. Ceilings and low visible will improve
by late Friday morning.
Valleys/mtns/deserts...mostly clear and VFR conds through Friday
an enhanced northwest swell will arrive to the coastal waters Saturday. The
swell is forecast to peak at 6 feet/16 seconds south of San Clemente
Island Monday evening...then begin lowering Tuesday. Elevated surf
conditions and strong rip currents are expected along exposed west
facing beaches Monday into early Tuesday.
California...Fire Weather Watch from Saturday afternoon through Sunday
afternoon for the Orange County coastal areas...Riverside
County mountains-including the San Jacinto Ranger district
of the San Bernardino National Forest...San Bernardino and
Riverside County valleys-the inland Empire...San Bernardino
County mountains-including the mountain top and front
country Ranger districts of the San Bernardino National
Forest...San Diego County inland valleys...San Diego County
mountains-including the Palomar and Descanso Ranger
districts of the Cleveland National Forest...Santa Ana
Mountains-including the Trabuco Ranger district of the
Cleveland National Forest.