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Area forecast discussion 
National Weather Service San Diego California
904 am PDT Wednesday Oct 1 2014

Synopsis...
a weak coastal eddy will weaken today...and low clouds and fog along
the coast should dissipate as well. A building high pressure ridge
aloft and offshore flow at the surface will bring increasingly
hotter and drier weather for Thursday through Saturday...especially
along and west of the Lower Mountain slopes. Day-time highs are
likely to reach 10 to 20 degrees above normal in these areas. The
offshore flow will also bring gusty northeast to east winds at times
for Thursday into Saturday...strongest Thursday morning. Weak
onshore flow and some weakening of the ridge is expected to bring
slightly cooler conditions for the coast on Sunday...but conditions
will still be quite hot elsewhere. Continued slow weakening of the
ridge Monday through Wednesday...resulting in continued gradual
cooling...and a return of night and morning low clouds and fog along
the coast and possibly into the western valleys.

&&

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

A weak coastal eddy has developed overnight which has resulted in
better stratus coverage into the coastal and western valley areas of
San Diego County according to morning visible satellite
imagery...with patchy stratus in coastal Orange County. The 12z
Miramar sounding shows a 3 degree marine layer inversion at around
1700 feet...with weak south flow at the surface from the eddy...and
west flow aloft. The eddy is expected to diminish by late morning
according to local WRF and MOS guidance...and so is the stratus.
Meanwhile...temperatures may rise slightly today as a ridge to the
west starts to build into the area.

Water vapor satellite currently shows a trough moving into the Great
Basin region. Surface high pressure will start to build over that
area in the troughs wake...and produce strengthening offshore
pressure gradients in our area. Gusty offshore winds are likely to
start in the San Bernardino County mountains and Cajon Pass area by
late this afternoon...with winds increasing in coverage and strength
tonight though Thursday morning. Forecast models indicate offshore
pressure gradients about 1 mb stronger than previous runs were
showing...at around 10 mb from San Diego to Tonopah...and 12 mb from
San Diego to Salt Lake City. There is not much upper level support
for winds...with 850 mb winds only at around 15-25 knots according to
local WRF. However...cansac_wrf continues to show 25-35 miles per hour
sustained with possible northeast to east 45-50 miles per hour gusts through
and below the Cajon Pass and San Gorgonio Pass...along the Santa Ana
foothills...and along the coastal slopes of the San Diego County
valleys. Thus...these areas may reach Wind Advisory criteria
Thursday morning. Offshore gradients will weaken later Thursday and
continue a slow weakening trend through Saturday...although the
previously mentioned favored areas may still see northeast to east
gusts to 35 miles per hour at times.

Meanwhile...the ridge mentioned earlier will continue to build over
the region Thursday into Saturday. This...in addition to the
offshore flow...will result in increasingly hotter days...with
day-time highs reaching 10-20 degrees above normal for Friday and
Saturday in the valleys...coast...Santa Ana Mountains/foothills and
Lower Mountain slopes. Saturday looks to be the hottest day
overall...although some coastal locations may experience their
hottest conditions on Friday due to the slightly better offshore
flow on that day. Expected day-time highs for Friday and Saturday
are as follows...low to middle 100s in the inland Empire...upper 90s to
low 100s in the San Diego valleys and inland Orange County...90s in
the lower elevations of the Santa Ana Mountains/foothills...and low
to middle 90s a few miles inland of the coast. A heat advisory has been
issued for Friday through Sunday for the valleys and the Santa Ana
Mountains/foothills. A heat advisory has also been issued for the
San Diego and Orange County coastal areas and the lower slopes of
the mountains for Friday through Saturday...with highest
temperatures occurring inland from the beaches. Slight cooling is
likely to occur at the coast Sunday due to possible weak onshore
flow and weakening of the upper level ridge.

The ridge will continue to slowly weaken Monday through
Wednesday...resulting in slow cooling each day...and gradually
increasing night and morning low clouds/fog along the coast and
western valley areas. Day-time high temperatures may finally reach
near normal by Wednesday.

&&

Aviation...
011445z...coasts/valleys...stratus with bases 1200-1600 feet mean sea level
gradually clearing to the coast 16-18z. Patchy clouds may linger
along the immediate coast through the afternoon...pushing back into
the coastal areas around 03z and up to 10 Michigan inland overnight. Ceilings
will likely begin around 1000-1500 feet mean sea level...lowering to 500-1000 feet
late tonight as offshore flow develops. Clearing will occur by
02/12z Thursday in Orange County...and 14-16z in San Diego County. Visible
may locally drop to 1sm or less over higher coastal terrain in San
Diego County Thursday morning. Northeast winds with surface gusts 25-35 knots
will develop below the Cajon Pass and Santa Ana foothills late
tonight...including near kont. Low level wind shear and moderate uddfs possible near the
coastal foothills of the San Bernardino and Santa Ana Mountains with
these winds.

Mtns/deserts...clear with unrestricted visible through Thursday morning. NE
to east winds with surface gusts 35-45 knots developing through the
passes...canyons...and coastal slopes of the mountains as well as the far
north Coachella Valley by 02/12z.

&&

Marine...
800 am...no hazardous marine weather is expected through Sunday.

&&

Fire weather...
high pressure aloft and offshore flow with locally gusty northeast
winds will bring much warmer and drier conditions for Thursday
through Sunday. Strongest winds...with local gusts to around 40
miles per hour...are expected for late tonight into Thursday morning...followed
by gradual weakening Friday and Saturday. Friday and Saturday will
be the warmest days...especially inland where temperatures of 95 to
105 degrees are possible. Slow cooling may begin near the coast on
Sunday as weak onshore flow returns. Humidities will fall
Thursday...reaching the middle teens by late morning for inland areas.
Expect lowest daytime humidities of 5 to 10 percent for inland areas
Friday and Saturday with poor overnight recovery. Humidities are
expected to slowly recover for Sunday into early next week as weak
onshore flow returns. While more widespread areas meeting red flag
warning criteria is not expected...warning criteria will likely be
met in some locations on Thursday...mainly below the Cajon
Pass...west of the Banning pass...portions of the coastal foothills
of the Santa Ana Mountains...and portions of the San Diego
foothills. Regardless...there will be an elevated threat for
wildfires Thursday into Sunday.

&&

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

&&

Sgx watches/warnings/advisories...
California...heat advisory from 11 am Friday to 8 PM PDT Saturday for the
Orange County coastal areas...Riverside County mountains...
San Bernardino County mountains...San Diego County coastal
areas...San Diego County mountains.

Heat advisory from 11 am Friday to 8 PM PDT Sunday for the San
Bernardino and Riverside County valleys-the inland Empire...
San Diego County valleys...Santa Ana Mountains and
foothills.

Pz...none.

&&

$$

Public...Harrison
aviation/marine...sunset
fire weather...pg

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