Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
930 PM PDT Wednesday may 6 2015
Synopsis... a deep low pressure system will bring colder weather
Thursday and Friday along with scattered showers and isolated
thunderstorms. Gusty west winds will continue in the mountains and
deserts. Continued cool Saturday...then dry and warmer Sunday and
Monday with weak high pressure aloft.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
A deep 550 dm closed low over Oregon this evening will move rapidly
southward tonight aided by a powerful 110 knots jet stream. By Thursday
afternoon it will be over central California and intensify into a
548 dm low. Areas of light rain may begin in so-cal tonight and
continue through Thursday as the moist layer continues to deepen
increasing onshore flow. The best chances for showers and
thunderstorms will be Thursday afternoon through Friday when positive vorticity advection is
optimized and the 500 mb cold pool descends over so-cal. Boundary
layer moisture deepens to around 8000 feet Thursday night...briefly
spiking above 10kft Friday morning. Precipitation is becoming more
of a certainty with this storm and probability of precipitation were raised in the evening
Storms of this nature produce highly variable precipiation totals.
The greatest precipitation totals will likely be over the foothills and the
west facing mountains slopes where enhanced orographics will produce 1-2"
in some areas. Precipitation totals west of the mountains will vary quite a
bit...ranging from 0... a 0.50-0.75" or more in those
areas beneath the stronger cells. The lower deserts will not see
much precipitation from this system since most of precipitation will be wrung out
over the mountains...and only a trace to a tenth of an inch is
expected. Snow levels will lower to around 5500 feet in San
Bernardino County and Montana San Jacinto where a few inches of snow
A second weaker shortwave trailing the main vorticity maximum will sweep
across so-cal Friday evening. Cold instability showers and island
banding is possible in San Diego County Friday night.
Friday will be a cold day with highs in the low to middle 60s west of
the mountains...the 30-40s in the mountains...and the low 70s in the
lower deserts. Some record low maximum temperatures may be broken.
Saturday will be a mostly dry and cool day in cold northwest flow
behind the departing low. Warmer Sunday and Monday with weak high
pressure over the southwest. Another trough will bring cooling and a
deeper marine layer Tuesday.
070400z...coast/valleys...widespread stratus will continue over the
coastal basin through Thursday with layers from near 2500 feet mean sea level to 5500
feet mean sea level. Visible generally unrestricted...except occasionally for local
terrain above 2000...and locally in possible light rain showers
overnight. Low to moderate confidence in ceiling heights and timing in
the tafs due to possible light rain showers and discontinuous trends
in coverage of the various layers.
Mts/deserts...clear skies with unrestricted visible...except the coastal
slopes which will be largely obscured in clouds. West winds of 20-30
kts with higher gusts over the ridges...along the desert slopes...
and locally into the deserts will create areas of up/down drafts and
low level wind shear over and east of the mts. Strongest west winds of 30-40kt with
gusts of around 50 knots will continue through and below the San
Gorgonio Pass...north of Palm Springs.
900 PM...there is a chance of thunderstorms and isolated cloud-to-
water lightning strikes over the coastal waters Thursday night into
early Friday. Otherwise...no hazardous marine weather is expected
900 PM...surf has gradually subsided today along with a fading
southwest swell. The south swell will continue to fade through
Thursday...along with the very strong the rip currents...especially in
Orange County. A shorter-period west swell will fill in and keep the
surf moderate along the San Diego County coast on Thursday. For surf
details see the surf zone forecast (laxsrfsgx).
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...Wind Advisory until 3 am PDT Friday for the apple and Lucerne
valleys-San Diego County deserts-San Gorgonio Pass near Banning.