Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
408 am PDT Sat Jul 30 2016
increasing monsoonal moisture will bring a little greater chance
for afternoon and evening thunderstorms to the mountains and
deserts and the potential for flash flooding for this weekend.
This chance for afternoon thunderstorms near the mountains will
continue into the middle of next week. A gradual cooling trend for
inland areas will continue into the middle of next week with a
developing weak trough of low pressure near the West Coast
bringing drying of the monsoonal moisture for the latter part of
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
A thunderstorm complex over southwest and south central Arizona
Friday evening has pushed an outflow boundary across the lower
deserts since midnight pushing what would most likely have been an
impressive haboob across the lower deserts under the cover of
darkness. Winds gusted to near 90 at Gila Bend...but mostly less
than 50 mph across Imperial County and less than 40 mph for the
Coachella Valley and the San Diego County deserts. Visibilities
briefly dropped below 2 miles at el centrol...and 1 mile at
thermal and Palm Springs. The east winds have also pushed through
the mountains of Riverside and San Diego counties and through the
Banning pass with the temperature at Beaumont jumping from 71 to
81 with the passage of the outflow boundary and the dewpoint
increasing into the 60s.
On Friday afternoon...there were isolated thunderstorms in the
mountains along the desert slopes. This increase in lower level
moisture is expected to increase the thunderstorm coverage and
potential for flash flooding a little for this afternoon and early
Friday evening aircraft soundings showed an increase in the marine
layer depth to around 1800 feet. Stratus coverage over the coastal
waters is more widespread than 24 hours ago...but with the arrival
of the thunderstorm outflow aloft...stratus which was near the San
Diego County coast has pushed back offshore a little.
Model quantitative precipitation forecast from the higher resolution models shows slight drying
for Sunday...but that most likely is absent any influx of lower
level moisture should there be another round of convection in
Arizona this evening or tonight pushing more outflow across the
With the increase in monsoonal moisture and the deepening of the
marine layer...cooling is expected through the weekend into early
A developing weak trough of low pressure near the West Coast next
week will keep drier southwest flow aloft not too far away to the
west. Residual monsoonal moisture may be sufficient to maintain
the chance of afternoon thunderstorms near the mountains through
Wednesday or Thursday before the southwest flow aloft pushes the
monsoonal moisture off to the east.
Inland cooling is expected to continue through the middle part of
next week with some warming of inland high temperatures toward
next weekend as drying aloft occurs.
301030z...coast and valleys...p6sm sct150, except for patchy marine
stratus extending from the coastal waters inland up to 15 miles with
bases 1000-1300 feet mean sea level and tops below 2k feet mean sea level through 16z. Local
vis 1-3sm in br where stratus intersects higher coastal terrain.
Mountains...p6sm scattered-bkn150 with isold/sct thunderstorms possible
after 18z through 02z Sunday with strong uddfs and low level wind shear. Local east
winds 20g30kt through and below the passes through 13z.
Deserts...outflow from thunderstorm activity over Arizona earlier in the
night will produce areas of southeast winds 20g30 knots and 1-3sm vis
restriction in blowing dust through 13z. Areas of 3-5sm vis
restriction due to dust may linger until around 15z, otherwise 5sm
in dust through 16z and then p6sm sct150.
no hazardous marine weather is expected through Wednesday.
a south swell from 200 degrees at 2-3 ft with a period of 18
seconds, will build into the coastal waters on Sunday afternoon.
This will produce elevated surf and strong longshore currents,
increasing the risk for strong rip currents and dangerous swimming
conditions late in the day. The surf/swell is forecast to peak
Sunday evening around the time of high tide which may result in
minor tidal overflow at susceptible beaches.
Skywarn activation may be needed for the mountains for this
afternoon and early evening.