Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
930 am PDT Tuesday may 5 2015
Onshore flow will continue the cool weather through Wednesday with
gusty west winds in the mountains and deserts and a continued deep
marine layer west of the mountains with widespread stratus and
patchy coastal mountain slope fog. There could be local drizzle late
tonight and early Wednesday. A cold low pressure system from the
north Thursday through Friday will bring additional inland
cooling...stronger gusty west winds in the mountains and
deserts...and periods of showers along and west of the
mountains...mostly likely Thursday night and Friday. Dry weather
will return Saturday with a warming trend Saturday through Monday
under high pressure.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Widespread stratus was occurring from the mountains west to the
coast in a 5500-foot deep marine layer. There was patchy fog in the
mountains along the coastal slopes. Only partial clearing will occur
today as the sounding is unstable below the inversion...and some new
clouds will likely form in areas that have sunshine. The deep marine
layer will mean that areas west of the mountains will be about 5 degree
f below normal...but temperatures in the lower deserts will only be
slightly below normal as 850-700 mb temperatures are similar to those from
Monday. Not much change in the marine layer is expected Wednesday.
The low pressure system from Monday is now over the central
rockies...with a short wave off the central California coast. The
main upper low is over SW British Columbia. The short wave could
interact with the deep marine layer to bring drizzle or possibly
very light showers late tonight...though the chance of measurable
precipitation is very low. The upper low over British Columbia will divergence
south and reach central California Thursday and inland Southern
California by Friday. Models have been in reasonably good agreement
with the tracking of the low. The low should bring some precipitation to
areas from the mountains west to the coast...especially since there
will be onshore trajectories from the coastal waters...and
precipitable water values will be up to 0.8 inches. 500 mb temperatures of -
25 degree c...quite low for may...will bring a chance of
thunderstorms...especially in San Bernardino County closer to the
low. 700 mb temperatures could lower to -7 degree c with 850 temperatures as low as 2
degree c...so the snow level could lower to 5500 feet or so late
Thursday night/early Friday. Precipitation amounts will be variable due to
the convective nature...but local amounts up to one inch could occur
in heaviest showers/thunderstorms...with most areas probably getting
around 1/4 inch. Most of the activity should shift to the east
Saturday morning...with ridging for late saturdsy through Monday and
temperatures recovering to near normal by Sunday.
051440z...coast/valleys...widespread stratus with bases around 3500
feet mean sea level and tops around 4000 feet becoming scattered 3500-4000 feet mean sea level with
areas of broken 3500 and tops around 4500 feet mean sea level after 18z. Visible will be
unrestricted. High confidence that the marine stratus layer will
increase again after 03z...with similar bases and tops expected
through Wednesday morning.
Mtns/deserts...coastal slopes between 3000 and 4500 feet mean sea level obscured
at times through Wednesday. Otherwise VFR with unrestricted visible. West winds
20-25 knots with gusts to 35 knots will produce moderate uddfs/low level wind shear over and
east of the mountains mainly after 21z through 15z Wednesday. Stronger west winds of
25 to 35 knots and gusts 45-50 knots are likely through and below the San
740 am...no hazardous marine weather is expected through Saturday.
However...northwest wind gusts of around 20 knots are likely
afternoons and evenings through Friday...mainly in the outer waters
near San Clemente Island. Also...some showers are possible Thu/Fri.
740 am...south-southwest swells continue today at about 4 feet with a
17 second period. Widespread surf of 3 to 7 feet will continue...with
sets of 8 to 11 feet possible along south-facing beaches. Strong rip
and longshore currents...beach erosion and minor tidal flooding of
low-lying coastal areas during the evening high tide is likely. A
high surf advisory is in effect through this evening. On
Wednesday...the swell is expected to decrease below 4 feet with
decreasing surf. The swell will continue to fall Thursday and
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...Wind Advisory from 4 PM Wednesday to 3 am PDT Friday for apple
and Lucerne valleys-San Diego County deserts-San Gorgonio
Pass near Banning.
High surf advisory until 11 PM PDT this evening for Orange
County coastal areas-San Diego County coastal areas.