Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
350 am PST Wednesday Nov 26 2014
high pressure aloft and weakening offshore flow will bring a warming
trend into Thanksgiving day with well above average high
temperatures for the coast and valleys. A return of onshore flow
will bring a cooling trend for Friday through the weekend and a
return of night and morning coastal low clouds and for. For Monday
through Wednesday of next week...a Pacific low pressure system could
bring moderate to heavy precipitation.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Short term (today through friday)...
surface high pressure over the Great Basin continues to weaken.
Locally gusty east to northeast winds will continue near the coastal
foothills today...but should mostly remain below advisory strength.
Further weakening of the winds will continue into Thanksgiving day.
High pressure aloft combined with the weakening offshore flow will
continue the warming trend into Thanksgiving day with high
temperatures in the 80s for inland coastal areas into the
valleys...10 to 15 degrees above average today...and 12 to 18
degrees above average on Thanksgiving. Warmest high temperatures
could be near 90. For some inland coastal and western valley
Weak onshore flow will return for Friday bringing slight cooling in
the deserts and 4 to 8 degrees of cooling west of the mountains.
Long term (saturday through tuesday)...
onshore flow will bring continued cooling for the weekend and a
return of night and morning coastal low clouds and fog. For Monday
through Wednesday...a Pacific low pressure system could bring
significant precipitation to much of California. There continue to
be model differences with the timing and details. The trend of the
past 24 hours is for this system to be slower and more closed. The
06z GFS...both the operational run and the 13-km parallel soon to be
operational run offer a reasonable forecast given the trends of the
past 24 hours with the Gem similar. This is slower and more closed
than the 12z European model (ecmwf) and earlier runs of the GFS. The 00z European model (ecmwf) is
significantly slower and more closed than the 12z European model (ecmwf) and the
slowest of the models but cannot be completely discounted
considering the trends of the past 24 hours.
A weaker shortwave will move inland across Southern California early
Sunday. This should pass through largely dry...but there is a small
possibility of mainly light precipitation along and west of the
mountains with its passage.
Based on the timing and details of the 06z GFS....Sunday night and
much of the day Monday would be largely dry...but a weak lower level
warm advection pattern combined with an influx of lower level
tropical moisture could bring some mainly light precipitation for
Sunday night into Monday. More significant precipitation is possible
for Monday night into Tuesday. The slower and more amplified model
solutions allow for tropical moisture to be tapped with the 06z GFS
increasing precipitable water values early Tuesday morning to nearly
1.5 inches as far north as San Diego...around 200 percent of normal.
The slower European model (ecmwf) timing would delay the arrival of more significant
precipitation until Tuesday into Wednesday.
The potential remains for rainfall amounts exceeding one inch at the
coast to 5+ inches in some mountain locations.
261000z...clear skies with unrestricted visible today and tonight. Local
surface northeast winds in foothills will produce up/down drafts and
isolated low level wind shear through 20z.
200 am...no hazardous marine weather is expected through Sunday.
a red flag warning remains in effect through this afternoon for the
mountains and inland valleys of Riverside and San Diego counties.
Gusty east to northeast winds will slowly decrease for later this
morning through this afternoon with strongest gusts early this
morning mainly 35 miles per hour or less. Lowest daytime humidities today of 5
to 10 percent. Weaker east to northeast winds will continue into
Thanksgiving day with a slight recovery in humidities.
Onshore flow will return on Friday and strengthen through the
weekend with a cooling trend with increasing humidities. A Pacific
low pressure system could bring significant wetting precipitation
for late Monday into Tuesday or early Wednesday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...red flag warning until 6 PM PST this evening for the Riverside
County mountains-including the San Jacinto Ranger district
of the San Bernardino National Forest...San Bernardino and
Riverside County valleys-the inland Empire...San Diego
County inland valleys...San Diego County
mountains-including the Palomar and Descanso Ranger
districts of the Cleveland National Forest.