Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Diego California
940 am PDT sun Apr 20 2014

Synopsis...
high pressure will bring predominately clear skies and warmer
conditions through Monday. However...a shallow marine layer will
remain along the coast...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 and
Friday. However...another stronger trough will move inland across
the west for the weekend...bringing the return of cooler conditions
and gusty west winds.

&&

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

Water vapor imagery shows a weak ridge of high pressure over
Southern California this morning....as a trough of low pressure
develops over the eastern Pacific. As a result...predominately
clear and sunny skies are prevailing on this beautiful Easter
morning. However...some low clouds are lingering along the
coast...with partly to mostly cloudy skies there. The 12z knkx
sounding shows two separate inversions this morning...with one near
1500 feet and a second lower just off the surface around 500
feet...which corresponds well with current cloud heights. The
sounding also shows that the inversion strength is around 6
degrees...with near 8 degrees of warming just above the surface.
Therefore...believe the inland areas will see some decent warming
today...with daytime temperatures running 3 to 8 degrees warmer than
those of yesterday. Coastal areas though will be modified by this
shallow marine layer...so think these areas will be similar to or
only slightly warmer than yesterday. There is also a question as to
whether or not the marine stratus will clear? The local WRF would
suggest no...but think most beach areas will see some sun today.
Otherwise...expect this warm conditions to continue into Monday...as
this ridge remains over the Southland.

The trough over the Gulf 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 big 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.

A transitory ridge will then build back across the region for
Thursday and Friday. 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 the
weekend. At this time...the models are still varying on the
strength and timing...so there is still quite a bit of
uncertainity. In fact...it appears that the latest GFS is now
trying to speed this system up...besides being the most aggressive
with it. The GFS also suggests that Southern California could see
some light precipitation. Meanwhile..the European model (ecmwf) only shows the
potential for some marine layer drizzle...as it some what washes out
the system as it moves inland. The Gem is then a compromise between
the two. For this reason...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.

&&

Aviation...
201517z...coast/valleys...patchy stratus about 5-10 sm
inland...mainly over southern Orange County and most of San Diego
County with bases around 1000 feet mean sea level...tops around 1500 feet mean sea level and
local visible 3-5sm...will clear to the coastal waters through 1800 UTC.
1800-21/0200 UTC...mostly sky clear and unrestricted visible. 21/0200-0900
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.

Mtns/deserts...few-sct clouds at or above 10000 feet mean sea level forming over the mountains
1800-2300 UTC. Otherwise...unrestricted visible and mostly sky clear through
Monday morning.

&&

Marine...
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
Wednesday.

&&

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