Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
200 PM PST sun Nov 23 2014
offshore winds prevailed over the region this afternoon...with
strongest winds occurring over San Bernardino and Orange counties.
Offshore flow will continue through Thursday...with a full fledged
Santa Ana event expected for Tuesday and Wednesday. Afternoon
relative humidity values in the single digits and high temperatures
5-15 degrees above average are in store for Monday through Thursday.
Winds will turn onshore by Friday...ushering in cooler weather for
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Southern California remains caught between a ridge off the West
Coast and a broad trough over the center part of the country this
afternoon. In the wake of a shortwave that moved rapidly through the
central rockies overnight...an area of high pressure is building
over Nevada. This has turned local pressure gradients offshore...with
san-tph currently at -6.4 mb. A change of -13.9 mb from the +7.5 mb
at 3 PM yesterday. As of 1 PM easterly gradients transitioned to
weakly offshore or neutral...with san-nyl at -0.1. Flow induced by
these offshore gradients is combining with weak to moderate low to
middle-level winds to bring locally gusty winds the the
passes...canyons...and coastal slopes this afternoon. Other than the
winds the weather remains quiet with only a few high clouds
propagating over the region from the northwest.
Through tonight...high pressure over Nevada will build to the southeast and
weaken...this will continue to force NE winds for the usual
passes...canyons...and coastal slopes. Temperatures will cool
quickly this evening...with a dry airmass in place and light to
moderate east to NE flow maintaining itself overnight.
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 gusts of +80 miles per hour are likely on Tuesday for the windy
corridors of the San Diego and Riverside County mountains and
valleys. Winds will remain strong in the favored locations of Orange
and San Bernardino counties as well...with frequent gusts over 40
miles per hour and local gust to 60 miles per hour on Tuesday. Santa Ana winds will weaken
slightly for Wednesday...and become weak to moderate by Thanksgiving.
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
the ridge off the coast will begin shifting slowly eastward on
Tuesday...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
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.
232116z...through 24/0000 UTC...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. NE
surface winds at kont and ksna will gradually taper off this
afternoon into early evening. Winds...up/downdrafts and low level wind shear
diminishing a little during the 24/0000-1200 UTC time-frame.
Also...north to NE winds 20-30 knots with gusts 35-45 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 continuing to
experience some strong northwest...north and NE winds...rotors 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.
116 PM...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 which would be hazardous to
small craft in those areas. 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 expected for Tuesday night through Friday.
a red flag warning is now in effect for strong gusty Santa Ana winds
and low humidity for Monday through Wednesday for the
mountains...coastal foothills...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 this evening...gusts to 45 miles per hour will
still be possible in the wind prone areas through Monday. The Santa
Ana winds will then strengthen significantly again for late Monday
into Tuesday...especially across the mountains and valleys of
Riverside and San Diego counties. 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...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 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 from 4 am Monday to 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 Monday to noon PST Wednesday for the
Riverside County mountains...San Diego County mountains...
San Diego County valleys.