Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
925 am PDT Thursday Jul 31 2014
high pressure will continue to build over the region today...with
slightly warmer conditions possible inland and a few high clouds
possible after the low clouds clear the coast. Subtropical moisture
will begin to spread across the region as early as Friday...with a
slight chance of afternoon mountain thunderstorms possible. A
better chance of showers and thunderstorms will develop this
weekend...as an upper level disturbances moves across the region.
Although residual moisture and instability will continue the threat
into Monday...dry and warmer conditions will return next week.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Water vapor imagery shows high pressure over the Desert Southwest
this morning...with the ridge axis just to our south. Water vapor
imagery also shows an outflow boundary lifting northwestward from a
remnant MSC over Mexico...in the form of high clouds. There is also
a surface boundary associated with this cloud deck...as dew points
northern Baja California and Imperial are on the rise...even though the models
do not show a moisture surge until tomorrow. That being said...what
moisture is coming north appears to be above 600 mbs...so do not
anticipate anything other than some high clouds . However...will
continue to watch this feature. Meanwhile...a shallow marine layer
has returned to the coast. The 12z knkx sounding shows that the
marine layer is around 1000 feet deep...with an eight degree
inversion. This marine air will help moderate temperatures along
the coast again today...while inland areas will be similar to or
slightly warmer than yesterday.
This ridge will begin to lift to our north tomorrow and for the
weekend...allowing a better surge of subtropical moisture to spread
into the area. Models are showing precipitable waters increasing to between 1.5 and
1.8 inches for Saturday and Sunday as well as disturbance lifting
across the region. However...there are some timing issues with this
disturbance. If you believe the 12z NAM...moves through on Saturday
and Saturday night...with all the activity east of US on Sunday. On
the other hand...the 12z GFS...which is still coming in...looks more
like a very consistent European model (ecmwf) at this time...lifting this disturbance
across Southern California Saturday into Sunday. The track of this
disturbance would even indicate the not only the potential for
nocturnal convection on Saturday night...but the threat of some
coastal thunderstorms once again. For now...want to wait to see
what the rest of the 12z GFS says as well as the 12z European model (ecmwf)...but
think they might have a better handle on the situation. This
disturbance would then shift east by Monday...with westerly flow
aloft developing. This would likely shut down any convective threat
for Monday...but there could be enough moisture for something to try
and develop over mountains. A gradual cooling trend will also
develop for Friday and the weekend. Otherwise...drier and warmer
conditions should develop for the work week.
311447z...coasts/valleys...patchy stratus 20 miles inland of the San
Diego coast...with bases 1100-1300 feet above mean sea level...tops
1300-1400 feet above mean sea level...and local visibility 3-5
miles...will clear to the coastal waters by 1700 UTC.
Elsewhere...unrestricted visibility and few-scattered clouds at or
above 15000 feet above mean sea level continuing. 1700-01/0500
UTC...unrestricted visibility and scattered clouds at or above 15000
feet above mean sea level. 01/0500-1500 UTC...patchy stratus gradually
forming within 20 miles of the coast...with bases 900-1200 feet above
mean sea level...tops around 1500 feet above mean sea level and local
visibility 3-5 miles. Confidence in timing of stratus for taf sites
is low...with moderate-to-high confidence in stratus occurrence.
Mountains/deserts...some cumulus clouds with bases around 9000 feet
above mean sea level developing over the mountains during the
1900-01/0200 UTC time-frame. Otherwise...increasing clouds at or
above 15000 feet above mean sea level through Friday morning.
747 am PDT...no hazardous marine weather expected through Sunday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.