Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
1045 am PST sun Nov 23 2014
winds over the region shifted from onshore to offshore
overnight...with strongest winds for today expected over San
Bernardino and Orange counties. Offshore flow will continue through
Thursday...with a full fledged Santa Ana event expected for Tuesday
and Wednesday. Low relative humidity values and high temperatures 5-15 degrees
above average are expected Monday through Thursday. Winds will turn
onshore by Friday...ushering in cooler weather for next weekend.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Southern California finds itself caught between a ridge off the West
Coast and a broad trough over the center part of the country this
morning. In the wake of a shortwave that moved rapidly through the
central rockies overnight...an area of high pressure is building
over Nevada. In response...local pressure gradients turned rapidly
offshore overnight...with san-tph currently at -6.6 mb. A change of
-14.1 mb from the +7.5 mb at 3 PM yesterday. In contrast west-east
gradients remain neutral to weakly onshore...with san-nyl at +0.5.
These gradient shifts...along with the north-northwest winds in the low to
middle-levels indicated by the 12 nkx sounding...are resulting in
moderate to locally strong north-NE winds over portions Orange and San
Bernardino counties. Outside of the winds...the weather is benign
this morning...with only a few high clouds propagating over the
region from the northwest.
Today and tonight...high pressure over Nevada will build to the southeast and
weaken...this will continue to force NE winds for the usual places
in Orange...San Bernardino...and Riverside counties. Gradients in
San Diego County should also come around and turn offshore by this
afternoon...bringing weak offshore flow to mountain and valley
locations. With the shift to offshore flow....highs for the upper
deserts and mountains will be 5-10 degrees lower than
yesterday...while areas west of the mountains will see a bump up of
3-5 degrees. Temperatures will cool quickly this evening...with a
dry airmass in place and light to moderate east to NE flow.
Monday into Thursday...offshore flow will remain in place through
this time period...bringing periods of strong Santa Ana winds and
increasing high temperatures to 10-15 degrees above seasonal
averages west of the mountains. The day of greatest concern remains
Tuesday...as the high currently over Nevada shifts southeast over Arizona and is
reinforced by a shortwave diving down The Spine of The Rockies. This
surface high position will promote an intense easterly surface
gradient...forcing strong east-east-northeast winds. Frequent wind gusts to 50 miles per hour
with local gust of +80 are likely on Tuesday for the windy corridors
of the San Diego and Riverside County mountains and valleys. Santa
Ana winds will weaken slightly for Wednesday...and become weak to
moderate by Thursday.
As is typical with these events...temperatures will be on the rise
west of the mountains. Upper 70s to low 80s will prevail on Monday
and Tuesday. By Wednesday and Thursday...the ridge off the coast
will shift inland increasing 500 mb heights to near 589 mb and
bumping high temperatures west of the mountains into the low to middle
80s. Our region will likely see the warmest temperatures in the
Continental U.S. For Thanksgiving day.
Friday and the weekend...the GFS and European model (ecmwf) are in good agreement
that the ridge along the West Coast will flatten in response to a
shortwave moving onshore in the Pacific northwest. This...along with
a transition to onshore flow on Friday...will bring cooler
temperatures and a return of the Marne layer along the coast.
231616z...areas of north to NE winds 20-35 knots with gusts 40-55 knots over
mountain ridges...through and below canyons/passes...along the
coastal slopes and into the coastal foothills will result in strong-severe
up/downdrafts...possible rotors and low level wind shear where winds to not surface
SW and west of the mountains...with winds strongest in the northern
areas. Strong NE surface winds will persist at kont this morning
before weakening in the late afternoon and evening. Strong NE
surface winds should also occur at ksna...likely starting by 1800
UTC...and continuing through the early afternoon before weakening in
the late afternoon. Surface winds and low level wind shear should not be an issue at
ksan and kcrq.
Also...north to NE winds 20-35 knots with gusts 45-55 knots over the Little
San Bernardino Mountains may locally surface in the Coachella Valley
and bring some low level wind shear to spots where the winds do not surface. Blowing
dust may reduce visible below 3 sm at times in the deserts through this
afternoon. Moderate confidence in kpsp and ktrm experiencing some
strong north winds and low level wind shear at times through 24/0000 UTC.
Otherwise...few-sct clouds at or above 20000 feet mean sea level and unrestricted visible
through Monday morning.
816 am...no hazardous marine weather is expected through Monday
On Tuesday...localized east to east-northeast wind gusts may reach
20-25 knots over the coastal waters. Confidence in winds this strong
occurring over the waters on Tuesday is low to moderate at this
time. Winds will begin to weaken late Tuesday afternoon. Then...no
hazardous marine weather for Tuesday night through Thursday.
Fire Weather Watch remains in effect for strong gusty Santa Ana
winds and humidities for Monday through Tuesday for the
mountains...valleys...and inland Orange County.
Moderate to locally strong Santa Ana winds will continue through
this afternoon...with strongest northeast winds occurring below the
Cajon Pass and in the Santa mountains and foothills. Although these
winds will diminish somewhat for late this afternoon...gusts to 45
miles per hour will still be possible in the wind prone areas through Monday.
These Santa Ana winds will then strengthen again for late Monday
into Tuesday...and spread southward into the mountains and valleys
of Riverside and San Diego counties. Although humidities will fall
today into the 10 to 20 percent range...with the lowest daytime
humidity values will occur on Monday through Wednesday...with
widespread poor overnight recovery developing. Gusty Santa Ana
winds will likely continue through Wednesday...favoring the eastern
slopes of Riverside and San Diego counties. Winds will continue to
decrease on Thanksgiving...with a slight recovery in humidities
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...High Wind Warning from 4 PM Monday to noon PST Wednesday for the
Riverside County mountains...San Diego County mountains...
San Diego County valleys.
Fire Weather Watch from late tonight through Tuesday afternoon
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 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.
High Wind Warning until 6 PM PST this evening for the Coachella