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Area forecast discussion 
National Weather Service San Diego California
123 PM PDT Friday Jul 29 2016

a strong ridge of high pressure aloft will bring very warm
conditions for inland areas today. Monsoonal moisture will produce
increasing chances and coverage of afternoon and early evening
heavy showers and thunderstorms over the mountains and deserts
through Tuesday. Some cooling expected this weekend as the ridge
weakens slightly, then perhaps some warming Monday and Tuesday due
to slightly stronger high pressure. The ridge will then weaken
again Wednesday through the rest of the week as a trough of low
pressure moves in along the West Coast, resulting in slow cooling.
Chances for afternoon and early evening thunderstorms decrease
Wednesday into Thursday due to drier air moving in. Patchy night
and morning marine layer low clouds and fog will continue to be
possible over the coast and western valleys.


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

Afternoon radar imagery shows stationary a stationary pulse
thunderstorm near Big Bear Lake, with the next nearest
thunderstorm activity occurring up in northeast San Bernardino
County. The 12z Miramar sounding shows a precipitable water value
of 1.34 inches which is almost exactly what it was yesterday.
Latest Storm Prediction Center mesoanalysis shows increasing instability over the
mountains and deserts, with 1000-2000 j/kg of surface based cape
indicated. The 19z hrrr shows a some showers and thunderstorms
developing over the mountains and high deserts this afternoon and
early evening, with the best chances over San Bernardino and
Riverside counties. As far as temperatures go, although the ridge
aloft is forecast to weaken slightly, models show 850 mb
temperatures remaining about the same today. Despite this,
temperatures are a few degrees lower than at this time yesterday
over the coast, San Diego County valleys and the deserts, with
temperatures in the inland Empire and mountains a little higher.
The higher dewpoints near 70 degrees in the coast and lower
deserts are likely to culprit for the lower temperatures. Meanwhile,
with the marine layer stratus having been so patchy the past
couple nights and the weather pattern not changing significantly,
am expecting any stratus along the coast tonight and Saturday
morning to be patchy once again.

Water vapor satellite shows a strong upper level ridge over the
Desert Southwest. Models show the ridge weakening through the
weekend which should bring some cooling. Then the ridge rebuilds a
bit Monday and Tuesday which could create slightly warming,
before a slow and gradual cooling trend begins again Wednesday
through the rest of the week as a trough moves in along the West
Coast and the ridge aloft weakens. Models also show monsoonal
moisture increasing from the east to southeast direction through
next Tuesday, with precipitable water reaching 1.4 inches
Saturday, 1.7 inches Sunday and Monday, and 1.8 inches Tuesday.
This moisture, in addition to instability produced by day-time
heating, will result in chances for afternoon and early evening
heavy showers and thunderstorms over the mountains and deserts
through at least Tuesday. Storm motion looks light on Saturday and
Sunday, which would increase the flash flood threat, especially on
Sunday when more low level moisture moves in. The storm motion
increases slightly from the east on Monday and Tuesday, which
could result in thunderstorms developing over the coastal slopes.
However, with a 700-300 mb wind of only 10 kt, it will likely be
light enough to continue to the higher flash flooding threat.

Although moisture starts to decrease Wednesday into Thursday,
wouldn't be surprised if there was still enough moisture and
instability to create isolated afternoon/early evening showers
and thunderstorms over the mountains on those days. Meanwhile,
onshore flow will continue to result in patchy night and morning
stratus/fog over the coast and western valleys.


292000z...coast and valleys...p6sm and sky clear-few100-150, except for
patchy stratus development late tonight between 30/10-16z over the
coastal waters, extending inland up to 10-15 miles with bases 800-
1200 feet mean sea level and tops at or below 1500 feet mean sea level. Local vis restrictions of 1-3
sm possible along the higher coastal terrain.

Mountains and deserts...p6sm and few-sct100-150 through this
evening, except for possible isolated thunderstorm development 20z-
02z along the ridge tops, especially San Bernardino County, and
across the High Desert with assoc uddfs and low level wind shear and occasional


no hazardous marine weather is expected through Tuesday.


Fire weather...
with increasing monsoonal moisture and instability, afternoon
and early evening thunderstorms are likely to develop over the
mountains and portions of the deserts through at least Tuesday.
The thunderstorms may initially produce dry lightning strikes
today and Saturday, and then becoming mainly wet strikes by


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


Sgx watches/warnings/advisories...


Public/fire weather...Harrison

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