Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
355 am PDT Tuesday Sep 16 2014
Corrected Skywarn action statement
moisture from Tropical Storm Odile will continue to spread
northward through Wednesday...elevating the chance for showers
and thunderstorms across Southern California. Some of the storms
may produce heavy rainfall and there will be a threat of flash
flooding...mainly during the afternoons and evenings near the
mountains. There will not be much relief from the heat and
humidity until Thursday when a trough of low pressure brings
cooling and drying from the northwest. Isolated showers and
thunderstorms are still possible into Friday over the mountains
and deserts...then partly cloudy weather with much more seasonal
temperatures for the upcoming weekend.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Well Odile (now a tropical storm) continues to churn north along
the eastern edge of Baja California California and possibly tapping some warm
water from the Gulf of California...although generally the
circulation is becoming very broad and losing it's inner core.
Models continue to have strong consensus to shift the remnants of
the tropical cyclone to the northeast beginning tonight and then
possibly reaching southern Arizona Wednesday night as a remnant
circulation. The best forcing is projected to be along the
northeast periphery of the remnant circulation.
Low level moisture has been streaming North Well ahead of the
system all night and may continue through today as well...although
the main axis of moisture will eventually get shunted to the east
as a trough of low pressure moves into coastal socal. When exactly
the low and middle level moisture gets shunted to the east...possibly
as early as Wednesday or as late as Thursday...will dictate the
possibility of precipitation especially for coastal locations. We
haven't made any significant changes early this morning to the
ongoing forecast database giving some uncertainty with related to
the tropical cyclone and interaction of the approaching upper
One change we've made is an increase in the probability of precipitation for this
afternoon and evening as hi res model instability projections are
decent and the super high res (hrrr) model is generating a
considerable amount of convection for this afternoon over the
mountains. The moist surge of low level moisture that took place
overnight has abated somewhat although decent southerly winds
continue out ahead of Odile. At this time our confidence is not
high enough to warrant a Flash Flood Watch for this afternoon but
that will be something to consider if the trends continue to look
a little more favorable for convection.
Hot temperatures will continue to be a concern for areas from west
of the mountains to the coast. An increase in low level moisture
will keep overnight temperatures quite warm tonight and may bring some
more record or near record warm min's tonight. The heat advisory
will remain in place through this afternoon.
For Wednesday our region may become more influenced by subsidence
on the northwest periphery of the tropical circulation...and with
the winding down of the system...the best moisture fetch will get
sheared well out to the northeast. Still there will be enough
residual moisture especially in our mountains and deserts to
generate scattered diurnally-driven convection Wednesday afternoon
and evening over the mountains and deserts.
For coastal areas of San Diego and Orange County...it now looks
like about the only chance for any measurable precipitation might be when
the upper low approaches the coast Thursday and Thursday night and
could help generate some showers over the coastal waters and the
adjacent coast. Then later into the upcoming weekend...the upper
low will bring some onshore flow and drier southwest flow aloft to
push any residual moisture well out of our area and bring an end
to even the low chance probability of precipitation. This will also bring a welcome cool
down for our region and much closer to seasonal temperatures.
160900z...a patch or two of low clouds could develop along the coast
this morning...but confidence is high that coastal aerodromes will
not be impacted. Cumulus buildups mainly over mountains this
afternoon with some turning into thunderstorms. These would have
bases around 10000 feet mean sea level with tops to 35000 feet. Erratic and
gusty winds around any thunderstorm. Scattered clouds at or above 12000 feet
mean sea level tonight.
200 am...no hazardous marine weather expected through Sunday.
Skywarn activation may be requested this afternoon due to possible
thunderstorms over the mountains and deserts. Activation is again
possible Wednesday afternoon in the same areas. Weather spotters are
encouraged to report significant weather conditions to the National
Weather Service as soon as is safely possible.
California...heat advisory until 7 PM PDT this evening for the Orange County
coastal areas...San Bernardino and Riverside County
valleys-the inland Empire...San Diego County valleys...
Santa Ana Mountains and foothills.