Area Forecast Discussion
Issued by NWS San Diego, CA

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468
FXUS66 KSGX 220549
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PST Tue Feb 21 2017

.SYNOPSIS...
Mostly cloudy conditions will occur overnight with patchy fog west
of the mountains. It will be cooler and breezy Wednesday through
Thursday as a trough of low pressure moves by to the north, though
it will most likely remain dry. Weak high pressure aloft will bring
dry and slightly warmer weather Friday through Saturday. A couple of
low pressure troughs will bring periods of rain Sunday through
Tuesday of next week, along with gusty winds in the mountains and
deserts.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

Mid and high clouds were drifting over the region. Patchy low clouds
and fog will form west of the mountains due to some marine layer
moisture moving in based on the local WRF, and the fog product shows
some stratus off the coast most of this evening so far, but the
stratus will not be widespread overnight. Ramona airport did just
have a visibility fall to 3/4 mile, and the lowest visibilities will
most likely be in the far inland valleys and lower mountain
foothills.

A broad upper level was off the northern California coast. Most of
the dynamics and moisture will stay to our north, but periodic
moderate amounts of moisture moving through aloft could bring
isolated sprinkles at times but no significant precipitation.
Increasing onshore surface pressure and height gradients will bring
gusty winds to the mountains and deserts with a few gusts in the 45-
55 mph range, especially through passes and along and just north and
east of crests. Cooler weather will return due to cooling aloft and
the stronger onshore flow, with highs Wed/Thu only in the lower 60s
west of the mountains. Eventually the trough will shift east into
the Plains by Friday with weak semi-zonal ridging over So-Cal
Fri/Sat for some warming, though temps west of the mountains will
mostly stay below 70.

An upper level low dropping south from the British Columbia coast
will combine with a subtropical jet to our southwest along with a
decent moisture fetch and PWs to around 1 inch. This will likely
bring moderate to locally heavy rain Sunday with a colder secondary
low possibly prolonging precipitation through Tuesday and bringing
some mountain snows. Models are not extreme with rainfall amounts,
but current estimates are for 1 to 2 inches west of the mountains
with possible higher amounts on the coastal slopes. Some winds could
occur as well in the mountains and deserts. The second low while
colder is also drier, but some substantial snowfall will be possible
at higher elevations, especially in San Bernardino County.

&&

.AVIATION...
220500Z...Scattered to Broken low clouds will form near the coast
and several miles inland after 08Z this evening, continuing through
about 14Z Wednesday morning. Bases will be 1200-1800 MSL with tops
2000-2500 MSL. Mid level clouds will continue at 7000-10000 feet.
Forecaster confidence has improved to moderate for the formation of
low ceilings overnight. VFR conditions will then prevail after 15Z
Wednesday morning. Gusty winds will be likely Wednesday afternoon
and evening, with the strongest winds over the mountains and along
the desert slopes with SFC gusts of 40 knots at times, with periods
of moderate wind shear and turbulence Wednesday afternoon and
evening.

&&

.MARINE...
Northwest winds and seas will increase Wednesday and continue
through Thursday. A swell from 280-290 degrees will build in on
Wednesday, peaking at 8-12 feet late Wed afternoon and evening with
a period of 14 seconds. The increasing winds and building swell will
result in hazardous boating conditions...and a Small Craft Advisory
continues in effect Wednesday through early Friday.

&&

.BEACHES...
Increasing westerly swell will bring high surf Wednesday and
Thursday. The swell will come in from 280-290 degrees at 14 seconds,
producing high surf late Wednesday with sets reaching 8-10 feet.
A High Surf Advisory is now in effect Wednesday through Thursday
night.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 1 PM Wednesday to 1 AM PST Thursday for Apple
     and Lucerne Valleys-Riverside County Mountains-San
     Bernardino County Mountains-San Diego County Deserts-San
     Diego County Mountains-San Gorgonio Pass Near Banning.

     High Surf Advisory from 7 AM Wednesday to 2 AM PST Friday for
     Orange County Coastal Areas-San Diego County Coastal Areas.

PZ...Small Craft Advisory from 7 AM Wednesday to 2 AM PST Friday for
     Coastal Waters from San Mateo Point to the Mexican Border
     and out to 30 nm-Waters from San Mateo point to the Mexican
     Border Extending 30 to 60 nm out including San Clemente
     Island.

&&

$$

PUBLIC...Maxwell
AVIATION/MARINE/BEACHES...JMB



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