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Area forecast discussion 
National Weather Service San Diego California
331 am PDT Thursday Jul 30 2015

Synopsis...
monsoonal moisture around strong high pressure over The Four Corners
region will continue to bring warm and humid weather into the
region through Friday. Showers and thunderstorms are likely today
and this evening with the strongest coverage over the mountains
and deserts. The airmass dries out over the weekend into early
next week for lower chances for afternoon thunderstorms over the
mountains and deserts. The marine layer will remain mainly over
the coast and portions of the valleys.

&&

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

A band of light rain is moving through southeast California early this
morning...across eastern San Bernardino and Riverside
counties...this feature is coincident with the middle level wave
that we've been tracking for the last few days. The middle level wave
will generally ride west-northwest this morning and move into south-central
California by late morning. Light rain band will cause the airmass
to stabilize for several hours through the middle morning...putting a
damper on the overall convective potential. However...very moist
southeast flow will continue with about 10-20 kts environmental flow
into the afternoon...and with partial sunshine we should expect
decent instability to form. With very little capping environment
we should see significant coverage of convection but with little
organization...in terms of strength of individual cells. Flash
flood potential will be dependent on the heavier cells and
training environment due to persistent southeast flow...with the greatest
flash flood threat over Riverside and San Bernardino counties this
afternoon and early evening. Convective potential will greatly
diminish after sunset this evening although isolated convection
could continue in those areas overnight.

Have continued the Flash Flood Watch with the greatest risk over
the northern mountains and the High Desert. Have increased the
probability of precipitation in this region as well. The chance for showers and storms
will be very small in the immediate San Diego coastal area...but
not non-existent...in this area of weaker instability and positive vorticity advection.

Some subtle ripples in the southeast flow will likely continue into
Friday with continued mention of chance probability of precipitation focused again over
the mountains and deserts.

Residual moisture and diurnal instability over the mountains and
high deserts will keep a slight chance of thunderstorms in the
forecast for this weekend...but overall a change to more of a SW
flow aloft in the synoptic pattern should gradually dry out the
atmosphere over this weekend...and re-establish the marine layer
weather close to the immediate coastal strip.

For early and middle next week...the large subtropical high will
actually sink to the SW and into northwest Mexico. This should
bring a slow increase in temperatures especially to our inland
locations...and squash our precipitation chances.

&&

Aviation...

300930z...coast/valleys...few/sct low clouds persist over the
coastal basin with bases near 1500 feet mean sea level and tops 2000 feet mean sea level.
These stratus clouds should not become a broken/overcast deck...due to high
clouds at or above 10000 feet mean sea level moving overhead. No visible restrictions
tonight. The low clouds will erode the coast between 30/1500-1800z.
There will be a slight chance of showers and thunderstorms through
this evening across the entire region. However...confidence on
timing is low and will be excluding thunderstorms in the vicinity from the tafs until higher
confidence is realized. Stratus with similar bases and heights as
this morning will be pushing inland after 31/0200z.

Mtns/deserts...a chance of showers and thunderstorms exists through
this evening across the mts and deserts. Greatest storm coverage
will be after 30/2000z. Thunderstorm cloud tops to 40000 feet mean sea level and
bases will generally be at or above 8000 feet mean sea level. The main threats
from these storms will be brief heavy rain...lowering
visibility...and frequent cloud to cloud and cloud to ground
lightning.




&&

Marine...

230 am...there is a slight chance of showers and thunderstorms over
the nearby coastal waters and estuaries through this evening as an
upper level disturbance moves over the area. Otherwise...no
hazardous marine weather is expected through Sunday.

&&

Beaches...

230 am...elevated surf on Wednesday caused a few problems including
strong rip currents at the beaches of San Diego County and southern
Orange County. The surf is subsiding today...but the risk of
lightning continues through the evening. Large rip currents are
possible and lightning...therefore the beach hazard statement will
continue through this evening. Surf conditions will improve slightly
during the day as the swell declines to around 2 feet at 14-15
second...but the rip current risk will remain high. The slow downward
trend in the swell will continue for Friday through the weekend.

&&

Skywarn...
Skywarn activation may be requested later today due to
thunderstorms and potential flash flooding.



&&

Sgx watches/warnings/advisories...
California...Flash Flood Watch through this evening for apple and Lucerne
valleys-Coachella Valley-Riverside County mountains-San
Bernardino County mountains-San Bernardino and Riverside
County valleys-the inland Empire-San Diego County deserts-
San Diego County mountains-San Gorgonio Pass near Banning.

Beach hazards statement through this evening for Orange County
coastal areas-San Diego County coastal areas.

Pz...none.
&&

$$

Public...Brotherton
aviation/marine...jt

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