Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Diego California
920 am PDT Friday Apr 18 2014

Synopsis...
a weak upper level low will move inland across Southern California
today...bringing plenty of high clouds as well as cooler conditions
and a few isolated showers to the mountains. A gradual warming
trend will then develop for this weekend and early next week...as
high pressure builds back across the region. However...the marine
stratus will linger near the coast...with areas of night and morning
low clouds and fog possible. A stronger and colder trough will then
move inland across the west on Tuesday and Wednesday...with cooler
conditions returning once again. A deeper marine layer will be
possible west of the mountains...with strong and gusty west winds in
the mountains and deserts. A minor warming trend will develop for
the remainder of the week.

&&

Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
counties...

Water vapor imagery shows a weak upper low over the Southern
California bight this morning...pulling plenty of high level clouds
across the region. The 12z knkx sounding shows a relatively
saturated profile above 600 mbs...with the marine layer around 3500
feet deep. As a result...precipitable water values are upwards of
0.93 inches. Unfortunately...there is a very substantial dry layer
between these two moist layers. Therefore...the weak echos on the
radar imagery are likely virga or just a few sprinkles. As this
upper level low moves over the region today...isolated showers may
be possible over the mountains...with just a few hundredths possible
at best. Otherwise...just expect today to be another cloudy
day...with a few more sun breaks possible than yesterday.
Temperatures will also be similar to or a few degrees cooler than
yesterday.

High pressure will then build back across Southern California for
this weekend and early next week...with dry and warmer conditions
developing. The inland areas will see the greatest warming
though...as a shallower marine layer lingers along the coast...and
continues to modify temperatures there. Another more potent trough
of low pressure will then move inland across the west on Tuesday and
Wednesday. Any moisture associated with this trough will stay well
to our north...but the marine layer will deepen and become more
widespread each night. The most noticeable difference will be with
our daytime temperatures. The current model runs are not quite as
cold today as they were yesterday...but daytime temperatures will
likely fall 5 to 15 degrees between Monday and Tuesday...before
falling another couple of degrees on Wednesday. Gusty west winds
will also develop in the mountains and deserts these days...with
blowing dust or sand a possible issue. As this trough shift east on
Thursday and Friday...a transitory ridge will briefly rebuild over
the region...with dry and warmer conditions possible.

&&

Aviation...
181525z...coast/valleys/mtn coastal slopes...bkn-ovc stratus from
2500 to 4500 feet mean sea level will continue through 1800 UTC...in addition to
multiple middle and high level cloud decks in the 12000-30000 feet mean sea level
layer. Mountain obscuration likely due to clouds. 1800-19/0000
UTC...stratus becoming scattered-broken 2000-4000 feet mean sea level...with middle and high
level cloud decks continuing. Also...there is a slight chance of high
based convection and virga that could produce brief isolated strong
downdraft winds during the day today. 19/0000-1500 UTC...bkn-ovc
stratus...with bases around 2000-2500 feet mean sea level and tops 3000-3500 feet
mean sea level...gradually forming in the same areas again with scattered-broken clouds
at or above 15000 feet mean sea Level. Mountain obscuration possible due to clouds.

Mountain desert slopes/deserts...multiple middle and high level cloud decks in
the 12000-30000 feet mean sea level layer and unrestricted visible will continue
through 19/0900 UTC...with clouds becoming scattered-broken thereafter. There
is a slight chance of high based convection and virga that could
produce brief isolated strong downdraft winds during the day today.

&&

Marine...
a trough of low pressure moving into California will bring west to
northwest winds of 20-25 knots and 6-7 foot short-period fresh swell
Tuesday evening through Wednesday evening...mainly for the outer
coastal waters. This may result in conditions hazardous to small
craft. Confidence in hazardous small craft conditions over the outer
waters during that time-period is moderate at the moment...with low
confidence in hazardous small craft conditions occurring over the
inner waters.

&&

Skywarn...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

Sgx watches/warnings/advisories...none.

&&

$$

Public...Palmer
aviation/marine...Harrison