Area forecast discussion
National Weather Service San Diego California
920 PM PDT Monday may 20 2013
Synopsis...
marine layer low clouds return to the coastal areas
tonight...burning off around middle morning on Tuesday. Mostly sunny
but not as warm on Tuesday. Noticeably cooler for Wednesday and
Thursday with the marine layer low clouds extending inland to the
foothills during the nights and mornings. Patchy drizzle will be
possible west of the mountains on Thursday morning. Daytime
temperatures will remain below seasonal averages through early next
week...with only minor day to day variations. Gusty west winds will
also develop each afternoon and evening in the mountains and
deserts...with the strongest winds on Thursday.
&&
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
counties...
The afternoon nkx sounding shows the marine layer about 2000 feet deep
with SW winds near the surface and weak NE winds above an eight degree
celsius inversion. The surface pressure gradients are beginning to trend
toward onshore...which likely accounts for the marine layer clouds
moving into the coastal areas several hours earlier than they did
the last couple of nights.
We remain under the influence of a weak upper ridge with the axis to
our northwest and dry northwest flow aloft. The ridge axis shifts over US on
Tuesday...so expect another day of warm conditions inland away from the
increasing marine layer influence closer to the coast.
By Wednesday...the ridge weakens and shifts to our east and is replaced by
an extensive low pressure system moving into the Pacific northwest...with the
associated trough extending southward as far as northern Baja California. This will
bring the onset of a significant cooling trend which will result in
daytime temperatures near or several degrees below seasonal averages on Wednesday
and even cooler on Thursday. Thursday is expected to be the coolest day as
cold air filters in from the northwest. As heights fall and cyclonic flow
aloft becomes established...the marine layer will deepen and result
in low clouds spreading inland to the foothills. A thickening low
cloud layer could even bring patchy drizzle west of the mountains on Thursday
morning. Increasing onshore pressure gradients and SW to west winds
aloft will also bring strong west winds to the mountains and adjacent
deserts each afternoon and evening. Thursday will likely be the windiest
day with gusts around 40 miles per hour possible in some areas.
Relatively cool conditions with extensive marine layer clouds and
fog during the nights and mornings...as well as strong onshore flow
will persist into early next week as the western U.S. Remains under
the influence of this persistent low/trough.
Some of the deterministic models are showing a vigorous shortwave
moving through the mean cyclonic flow which has the potential to
bring US some precipitation next Tuesday. However...this solution still has a
high degree of uncertainty.
&&
Aviation...
210330z...bkn-ovc009-014 tops 018 mean sea level spreading 15sm inland through
15z Tuesday. Between 15-18z Tuesday stratus clearing back to the coastal
waters.
Mtns/deserts...scattered high clouds and unrestricted visible through
Tuesday.
&&
Marine...
a 3-4 feet/16-17 second southwest swell through midweek with elevated
surf and strong rip currents on south and southwest facing beaches.
Highest surf from 4-6 feet will be on exposed southwest facing beaches
with a few sets to 7 feet.
A 6-8 feet short-period northwest wind swell will move into the outer
coastal waters Wednesday and Thursday resulting in choppy seas and
rough boating for small craft in the vicinity of San Clemente
Island. The swell will also bring elevated surf to exposed west
facing shores.
Increasing tidal swings this week with the approaching full moon on
Friday. A 7.2 feet high tide on Friday and Saturday nights will recede
to a -1.7 feet low tide Saturday and Sunday mornings.
&&
Sgx watches/warnings/advisories...none.
&&
$$
Public...pg
aviation/marine...moede
