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Area forecast discussion
National Weather Service San Diego California
914 PM PDT Tue Jun 27 2017

Synopsis...
stronger onshore flow will bring a cooling trend through Thursday
with high temperatures returning to near average for Wednesday and
Thursday. Low clouds and fog will return to coastal areas tonight,
and spread into some valleys into Thursday morning. Slightly warmer
Friday under weak high pressure, then seasonal Summer weather
prevailing through the Holiday weekend.

&&

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

Satellite imagery this evening showed clear skies prevailing over
socal once again, but marine clouds were gathering over the bight
and spreading toward the coast. The 00z Miramar sounding had a weak
inversion based near 1500 feet mean sea level and weak west winds below 3k feet.
The inversion was about 300 feet higher than last night, and the
inversion top was 5 degrees c lower than yesterday at 00z. Surface
pressure gradients showed good onshore trends, continuing to support
westerly winds of 15-25 miles per hour with peak gusts of 35-45 miles per hour through
wind-prone mtn/pass/desert areas.

A red flag warning remains in effect from the mtn crests, east into
the deserts of Riverside and San Diego counties. No forecast changes
this evening, cooling is on track.



From previous discussion...

Temperatures are a few degrees lower at 1 PM today than they were
yesterday at this time, except for the Lower Desert. A brand new
marine layer has come off the factory floor (along the central
coast), and this shiny new marine layer will drive into the Southern
California showroom tonight. This appears to be in response to a
shortwave moving by to our north, which has also flattened out the
monster ridge responsible for our recent heat. The relaxed intensity
of the high will help the intense heat take a chill pill in the
interior away from the marine layer, and the marine layer cruising
into Southern California will take care of the cooling west of the
mountains. Daytime temperatures will be noticeably lower Wednesday
and Thursday, especially west of the mountains. This new low cloud
deck is not a dense fog deck as was its predecessor at the coast
this morning. As the new coastal clouds move ashore, there might be
dense fog briefly on coastal mesas and hills, but true fog with low
visibility will not be an issue at the coast itself. As it moves
ashore this evening it should deepen overnight enough to spread into
western valleys. For the coming week, the stagnant summertime
pattern will have only very minor fluctuations between the influence
of a weak ridge or a weak trough over Southern California. Right now
we see relatively cool Wednesday and Thursday followed by a slightly
warmer Friday and Saturday, a cooler Sunday and Monday, and a warmer
Fourth of July. The coastal clouds will make it into some of the
westernmost inland valleys during the nights.

&&

Aviation...
280400z...coast/valleys...stratus will gradually develop tonight
over coastal areas, spreading into some valleys, to 15-25 miles
inland by 12z Wed. Bases will be 800-1100 ft mean sea level with tops to 1500
ft mean sea level. Kcrq will have a ceiling very soon with ksan likely by 06z and
ksna around 08z. Local vis below 1 mile will occur in some coastal
valleys, including vicinity krnm mainly 10z-15z. Most areas will clear
15z-18z Wed, with stratus returning early Wed night.

Mountains/deserts...clear skies with unrestricted vis will prevail
through Wed evening. West winds gusting 30-40 kt will occur over and
east of the mountains through 12z Wed, producing low level wind shear and MDT
up/downdrafts over and east of the mountains.

&&

Marine...
no hazardous marine conditions are expected through Sunday.

&&

Fire weather...
very low relative humidity will continue over the deserts and desert slopes of the
mountains through Wednesday with slight recovery Thursday. Winds
will become more localized however, limiting the areas and periods
of critical fire weather conditions, and confining them largely to
the deserts where fuel is limited. So the red flag will be allowed
to expire late tonight.

&&

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

&&

Sgx watches/warnings/advisories...
California...red flag warning until 1 am PDT Wednesday for Coachella Valley-
including the Palm Springs South Coast desert district-
Riverside County mountains-including the San Jacinto Ranger
district of the San Bernardino National Forest-San Diego
County deserts-including the Anza Borrego Desert State Park-
San Diego County mountains-including the Palomar and
Descanso Ranger districts of the Cleveland National Forest-
San Gorgonio Pass near Banning.

Pz...none.

&&

$$

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