Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service San Diego California
855 PM PDT sun Apr 20 2014
high pressure will begin to weaken on Monday as a low pressure
trough approaches from the west. Westerly winds will increase late
Monday and continue into early Wednesday over the mountains and
deserts as the trough swings through. Continued mild on Monday...
then cooler Tuesday and Wednesday with a deeper marine layer and
areas of night and morning low clouds and fog. Mostly sunny and
slightly warmer on Thursday...then increasing clouds...blustery and
much cooler with a chance of showers into the weekend as a Pacific
storm system moves across the state.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Marine clouds were evident in satellite imagery offshore and along
the north coast of San Diego County at 8 PM PDT while skies were
clear over the rest of the region. Surface pressure gradients were
1-5 mbs onshore and winds mostly light. The 00z Miramar sounding had
a weak 3 degree c inversion based near 1500 feet.
The main weather concern overnight will be for the development of
patchy dense fog. Dewpoints were well into the 50s at 03z west of
the mountains...and skies were mostly clear. With light winds
expected overnight...the hires models and BUFKIT soundings indicate
saturation of the marine layer. This should result in areas of
fog...becoming locally dense late night where a low cloud deck is
absent and dry offshore drainage from the interior does not prevail.
Any fog/ low clouds should burn off by middle morning on Monday...leaving
a fine and sunny day most areas with near or above average
temperatures. The sea breeze will hold temperatures in check along the
A weak high pressure ridge over socal this evening will drift east
on Monday as an upper-level trough approaches from the west. Onshore
gradients will begin to ramp up on Monday afternoon...and continue
through Tuesday as surface pressures fall over the Great Basin. Tuesday will be
much cooler west of the mountains as the onshore builds the marine layer.
Winds will likely reach advisory strength over the mountain ridges
and through the passes into the deserts by Tuesday afternoon through Tuesday
night. A few peak gusts of 55-60 miles per hour are possible...mainly in wind
prone areas of the deserts.
The trough will slide east on Wednesday/Thursday allowing temperatures to
recover somewhat and the marine clouds to thin before another large
area of low pressure is carved out across the eastpac. This is a
very energetic system for late April with a strong jet core well in
excess of 100 kts. There is plenty of potential with this system...
especially for central and northern California...but several model
runs are hinting at more of that energy dipping farther south. With
that in mind...a chance of showers has been introduced for next
weekend. Showers or not...expect strong onshore winds over the
mountains and deserts of socal this coming weekend...and cooler
210330z...coast/valleys...increasing stratus coverage through 14z
with bases 0800-1200 feet mean sea level and tops 1500 feet mean sea level. Areas of visible
3-5sm...with local visible at or below 2sm along higher terrain within 15 miles
of the coast. Conditions improving Monday morning with stratus
clearing from the coastal airports between 16-18z Monday. Between 02-06z
Tuesday...bkn-ovc015-020 returning to the coastal airports.
Mtns/deserts...unrestricted visible and mostly sky clear through Monday.
computer models are still projecting increasing west to northwest
winds across the coastal waters Tuesday. The strongest winds arrive
Tuesday evening with gusts to 25 knots over the outer waters...and from
15 to 25 knots over the inner waters. These winds combined with a 6-8
foot short-period swell will produce hazardous seas for small craft
over the outer waters. Lower confidence in Small Craft Advisory
conditions for the inner waters. Conditions will improve on
Friday and Saturday...another strong trough will move across
Southern California bringing strong winds and high seas next
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.