Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Diego California
140 PM PDT sun Apr 20 2014

high pressure will bring predominately clear skies and warmer
conditions through Monday. A shallow marine layer will linger along
the coast though...moderating temperatures...with night and morning
low clouds and fog possible. A trough of low pressure will then
move inland across the west Tuesday and early Wednesday...with
cooler conditions...a deeper marine layer...and strong and gusty
west winds in the mountains and deserts developing. A transitory
ridge will bring minor warming and lighter winds for Thursday.
However...another stronger trough will move inland across the west
for Friday night and the weekend...bringing the return of cooler
conditions...gusty west winds...and the potential for some light


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

Water vapor imagery shows a relatively Flat Ridge of high pressure
over Southern California this a trough of low
pressure continues to dig over the eastern Pacific. As a
result...skies are predominately sunny this afternoon...with warmer
conditions prevailing across the inland areas. However...visible
imagery does show a shallow marine layer already pushing into the
San Diego County beaches...with coastal temperatures running a few
degrees cooler than this time yesterday. These conditions will make
for a very pleasant evening across the region. The local WRF shows
an eddy develop late think the marine layer will likely
stay around a similar depth as last night...with coastal low clouds
redeveloping overnight tonight. Otherwise...expect tomorrow to be
very similar to this weak ridge remains in place.

The trough over the eastern Pacific will then shift inland across
the West Coast on Tuesday and early Wednesday...bring much cooler
conditions as well as strong and gusty winds. Daytime temperatures
across the inland areas will fall 8 to 15 degrees from Monday into
Tuesday...falling back to average or below average for this time of
year. The marine layer will also deepen in response to this
trough...but there may be enough cold air associated to mix out the
low clouds as it pushes inland on Tuesday. The local WRF continues
to trend this way...but then shows enough lingering moisture that
some low clouds may reform Tuesday night. The other story with this
trough will be with the gusty west winds in the mountains and
deserts. Onshore pressure gradients will likely increase to between
9 and 11 mbs between San Diego and Daggett...with the 850 mb and 30
above ground level winds increase to between 35 and 45 kts on Tuesday afternoon.
The latest models have backed off these winds a will hold
off issuing a high wind watch...but advisories will likely be needed
if currently trends continue.

A transitory ridge will then build back across the region briefly on
Thursday. This weak ridge will bring some modest warming to the
inland areas and lighter winds. However...another stronger and
potentially colder trough will dig along the West Coast for Friday
and the weekend. At this time...the models are still varying a bit
on the strength and timing...but the 12z European model (ecmwf) and GFS both came in
speeding up the timing of this trough by about 12 hours. They are
also both showing that some light precipitation could also fall
along and west of the mountains. Therefore...added a slight chance
of showers starting late Friday night and continued the threat
through Saturday. At this point in time...confidence is still not
high...but with the models coming into better is
definitely Worth a mention. The only thing that can be said with
certainty is that cooler conditions will develop along with gusty
west winds in the mountains and deserts...starting on Friday.


202013z...coast/valleys...through 21/0100 UTC...mostly sky clear and
unrestricted visible...except for some broken clouds 1000-1500 feet mean sea level within
3 sm of the central to southern San Diego County coast. 21/0100-0900
UTC...stratus forming within 5-10 sm of the coast...with bases
600-900 feet mean sea level...tops 900-1200 feet mean sea level...areas of visible 3-5sm...and
local visible at or below 2sm...mainly along higher coastal terrain. High
confidence in occurrence...moderate confidence on timing. These
conditions continuing through 21/1500 UTC. Clearing of stratus
21/1500-1800 UTC.

Mtns/deserts...few-sct clouds at or above 10000 feet mean sea level forming over the mountains
through 21/0000 UTC. Otherwise...unrestricted visible and mostly sky clear
through Monday morning.


west to northwest winds will strengthen Tuesday as a trough of low
pressure moves across California. The winds peak Tuesday night with
gusts around 25 knots over the outer waters...and gusts of 15 to
locally 25 knots over the inner waters. These winds will combine with a
6-8 foot short-period swell to bring hazardous seas for small craft
over the outer waters...with low confidence in Small Craft Advisory
conditions for the inner waters. Conditions will improve on


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


Sgx watches/warnings/advisories...none.