Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
128 PM PDT Sat Jul 4 2015
Synopsis... solid onshore flow at the surface and increasing
southwesterly flow aloft will guarantee some fine Summer weather
across the Southland through next week. A deep marine layer will
bring low clouds each night and morning well into the valleys...
which and may linger near the beaches into the afternoons. This will
mean cooler than average Summer days next week. There remains a
small chance of isolated thunderstorm activity near the mountains
this weekend...and patchy drizzle from the marine layer some days...
otherwise the weather will be dry.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Marine clouds were still extensive at midday over the California coastal
waters...but had burned off inland to the coastal strip. High clouds
covered portions of far eastern California and much of Arizona. A few cumulus had
developed over the mts of socal as well. Surface pressure gradients
were running 5-8 mbs onshore to the deserts...with a weak onshore
trend. The windiest desert passes had gusts to 25 miles per hour at noon PDT.
Temperatures west of the mts at noon PDT were running some 2 to 8
degrees f lower than yesterday noon....but it was still quite hot in
A Rex block over the far east Pacific this afternoon is not expected
to break down until the middle of next week. Meantime...a southerly
flow aloft around high pressure centered over The Four Corners area
will continue to advect monsoonal moisture northward into eastern
California...AZ...and Nevada. The edge of this deeper moisture is forecast to
remain just east of the County Warning Area...but is close enough so that weak
disturbances in the flow aloft could tap some of it and result in
isolated mountain/desert shwrs/tstms. For the now...the models support a
dry solution...but with towering cumulus over the mts much of the day...included
a slight chance into this evening there.
Any uncertainty regarding shower/thunderstorm development will be swept away
by the middle of next week as The Block breaks down over the
eastpac...and the low approaches the coast with increasing...dry SW
flow aloft. This pattern also favors solid onshore flow deep into
the interior for a deeper than average marine layer and cooler than
normal days. The models begin to rebuild the subtropical high back
over New Mexico and The Four Corners area after next week. Expect
warmer weather with a shallower marine layer then.
In the meantime...models show the marine layer deepening Sunday...
which could put it close to 3k feet deep. Some fluctuations are likely
through next week...but the pattern suggests it will remain near
2500 feet. This will bring nocturnal clouds/fog deep into the valleys
each night/morning...and hold maximum temperatures below average. Depending on
the inversion strength...this could result in limited clearing near
the beaches some days.
Aviation... 042000z...coast/valleys...low clouds...with bases from
1600-1900 feet mean sea level and tops to 2400 feet mean sea level...will likely linger along
the San Diego County coast this afternoon due to an 11 degree c marine
layer inversion. Stratus will become more broken/overcast late this
afternoon elsewhere along the coast...and push around 40 sm inland
by early Sun morning...with slightly higher tops and bases. Visible of 2-
4 sm br will be possible tonight where stratus nears higher terrain.
Similar clearing is expected Sun morning. Otherwise scattered-broken clouds
at or above 15k feet mean sea level and unrestricted visible through Sun morning. Forecaster
confidence in stratus forecast is moderate to high.
Mtns/deserts...sct-bkn clouds at or above 15k feet mean sea level and unrestricted visible
through Sun morning. Local west surface winds gusting 30-40 knots through
the San Gorgonio Pass and along the Desert Mountain slopes this
afternoon and evening with the normal sea breeze. Slight chance of a
light shower over the highest peaks this afternoon.
Marine... 100 PM...no hazardous weather is expected through
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.