Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
945 PM PDT Friday Jul 3 2015
Synopsis...dry and seasonal Summer weather is forecast over the
Holiday weekend. Marine layer clouds will retreat to the coast each
afternoon. Weak monsoonal flow aloft will continue over the
mountains and deserts but it appears too weak to produce any
showers. Next week will trend cooler with a moderately deep marine
layer and gusty afternoon winds in the mountains and deserts.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Southern California will be on the far western edge of the monsoonal
flow through Monday. South-southeast flow aloft between the upper
ridge moving into The Four-Corners region will entrain drier air
moving in from the west with the upper low 800 miles off the coast.
Normalized precipitable water averages around an inch over the
mountains and deserts Saturday through Monday...which is marginal
for precipitation potential. Much higher precipitable waters of 1.50" will be just east
of the area over the lower Colorado River valley. A slight jog to
the west of this moisture field would boost our precipitation chances...but
neither the cansac 2km WRF nor the local WRF suggest that
possibiltiy and generate zero quantitative precipitation forecast over the mountains through the period.
The 12z global European model (ecmwf) is also dry. The 00z gfs40 is the outlier this
evening with quantitative precipitation forecast over the mountains each afternoon. But the gfs40 has
been overestimating quantitative precipitation forecast lately and has been discounted. So with all
that being said...the forecast remains dry at this point and only
afternoon cumulus are expected over the mountains
Marine layer clouds will spread back into the valleys tonight and
then retreat back to the coast Saturday afternoon...then return to
the coastal zones Saturday evening. Impacts on viewing the fireworks
near the coast should be minimal with scattered-broken clouds with bases
around 1000 feet.
Next week a low pressure trough off the coast will move slowly east
and make landfall over central California on Thursday. Dry southwest
flow aloft ahead of the trough will shut down the monsoon and bring
strong onshore flow and gusty mountain and desert winds. The marine
layer will be unseasonably deep for July with clouds spreading into
the valleys. High temperatures will be slightly below seasonal
Aviation... 040300z...coast/valleys...patchy stratus currently
along the San Diego County coast will continue to fill in and spread
20-25 Michigan inland tonight with bases 1100-1400 feet mean sea level and tops to 2000
feet mean sea level. A few low clouds could briefly reach kont after 12z...though
there is low confidence in a ceiling there. Areas of higher terrain
in the valleys will be obscured with local visible below 3 Michigan in some
locations between 04/08z-15z. Clearing could be quite slow or even
partial Saturday near the coast...with coastal airports likely
clearing after 18z.
Mtns/deserts...local surface winds from the west 15-25 knots gusts 35-40 knots
will occur 22z through 08z tonight through the San Gorgonio Pass and
desert slopes of the San Diego County mountains otherwise broken clouds
at/above 15000 feet mean sea level and unrestricted visible will continue through
tonight...with decreasing clouds Saturday.
Marine... 800 PM...no hazardous weather is expected through
Skywarn... Skywarn activation is not requested. However weather
spotters are encouraged to report significant weather conditions.