Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
150 PM PST Monday Nov 24 2014
high pressure aloft will bring warm and dry conditions to Southern
California...while a surface high pressure over the Great Basin
brings periods of strong gusty Santa Ana winds through Wednesday.
The strongest winds will occur tonight through Tuesday
morning...with a secondary...but weaker peak on Tuesday night and
Wednesday morning. Onshore flow will return on Friday...with cooler
conditions prevailing through the weekend. Unsettled weather will
also return early next week...as a Pacific low moves inland across
California. This storm could bring periods of moderate to locally
heavy precipitation on Monday.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Water vapor imagery continues to show a large ridge of high pressure
centered along 130 west this afternoon...with north northwesterly
flow aloft over Southern California. A few thin high clouds are
continuing to filter through this flow...with predominately sunny
skies prevailing. Temperatures are warming nicely across the
area...with most coastal areas running 4 to 8 degrees warmer than
this time yesterday. This gradual warming trend will continue
through Wednesday...with only minor fluctuations for Thursday...as
this ridge remains our dominate weather feature for the next several
The main weather concern for the next few days will be with the
gusty Santa Ana winds. The surface gradients are starting to
increase this afternoon...and will peak late tonight and early
Tuesday morning. At this time though...the latest models runs
continue to trend weaker for this event...with the 850 mb winds only
running around 45 kts. There is still some decent support at 925 mb
though...especially in San Diego County...where the 12z WRF showing
some 50 to 55 knots winds. Believe the strongest gusts tonight and
early Tuesday morning will favor the west to east oriented canyons
of Riverside and San Diego County...even though most places will
still be gusty. Although these winds will gradually weaken through
Wednesday...a secondary peak will occur Tuesday night and Wednesday
morning...with most areas still seeing advisory level type winds.
These offshore winds will finally subside Thanksgiving day...as the
gradients become neutral.
Onshore flow will return on Friday...as the ridge of high pressure
begins to break down. As a result...expect a cooling trend to
develop for Friday and the weekend...with the marine clouds
returning to the coastal areas Friday night and Saturday morning.
That then brings US to our other main focus period of the forecast.
The extended models continue to show a rather impressive Pacific
storm developing and moving inland across California early next
week. There are still some timing issues...with the GFS trending
about 12 hours faster than the European model (ecmwf). That being said...all the
models are showing a decent soaking across Southern California.
Therefore...expect precipitation to spread across the region some
time between Sunday afternoon and night...with periods of moderate
to heavy rain developing on Monday. Snow levels will also fall to
around 6000 feet...so some accumulating snow possible over the
higher peaks. Except for the timing issues...this storm looks
promising...with good run to run consistency. Therefore...increased
the probability of precipitation to likely for Monday.
242110z...through 25/0300 UTC...areas of NE to east winds 15-25 knots with
gusts 30-40 knots over mountain ridges...through and below
canyons/passes...along the coastal slopes and into the coastal
foothills will result in moderate-strong up/downdrafts and low level wind shear where winds
do not surface SW and west of the mountains. After 25/0300 UTC...the NE
to east winds will strengthen to 25-35 knots with gusts 45-60
knots...resulting in strong-severe up/downdrafts...rotors and low level wind shear SW and west
of the mountains. Winds at kont and ksna should diminish around
25/0000-0200 UTC. For ksan and kcrq...low level wind shear likely to start around
25/0200-0400 UTC and continue into Tuesday morning. Kcrq may
actually have some 20 knots easterly surface winds by 25/1200 UTC but
confidence is low.
Otherwise...sct-few clouds at or above 20000 feet mean sea level becoming sky clear after
25/0300 UTC. Unrestricted visible through Tuesday morning.
110 PM...offshore wind gusts could reach 25 knots over the coastal
waters on Tuesday. Conditions that reach small craft conditions will
likely be localized and focused over the nearshore waters.
After Tuesday...no hazardous marine weather expected through
a red flag warning is in effect for strong gusty Santa Ana winds and
low humidity through Wednesday for the mountains...coastal
foothills...valleys...and inland Orange County.
Moderate Santa Ana winds will continue through this afternoon...with
strongest northeast winds occurring in the Santa mountains and
foothills as well as the coastal slopes of the San Diego County
mountains...with gusts to 45 miles per hour possible in the wind prone areas.
The Santa Ana winds will then strengthen significantly again for
late tonight into early Tuesday morning...especially across the
mountains and valleys of Riverside and San Diego counties as the
direction turns more easterly. These winds will combine with single
digit humidity values and poor overnight recoveries to elevate the
fire danger through Wednesday. Winds will continue to decrease on
Thanksgiving...though still somewhat gusty offshore...with a slight
recovery in humidities possible. Onshore flow will return for Friday
into next weekend with cooling and further increasing humidity.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...High Wind Warning until noon PST Wednesday for the Orange County
coastal areas...San Bernardino County mountains...San
Bernardino and Riverside County valleys-the inland Empire...
Santa Ana Mountains and foothills.
Red flag warning until 6 PM PST Wednesday for the Orange County
coastal areas...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 Bernardino County mountains-including
the mountain top and front country Ranger districts of the
San Bernardino National Forest...San Diego County inland
valleys...San Diego County mountains-including the Palomar
and Descanso Ranger districts of the Cleveland National
Forest...Santa Ana Mountains-including the Trabuco Ranger
district of the Cleveland National Forest.
High Wind Warning from 4 PM this afternoon to noon PST Wednesday
for the Riverside County mountains...San Diego County
mountains...San Diego County valleys.