Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
123 PM PST Sat Feb 13 2016
Synopsis... after a brief onshore push today...winds will turn back
offshore as high pressure rebuilds aloft and over the Great Basin.
Some coastal fog may develop again overnight...but drier air will
overspread the region on Sunday. Northeast winds will increase and
become locally strong and gusty again below some passes and canyons
into Monday...then weaken through Tuesday with unseasonably warm and
dry days. This will be followed by cooler weather Wednesday as
onshore flow returns. For Thursday...a low pressure trough moving
inland through the state will bring a chance of showers.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Possible dense fog along the coast again tonight...
Possible advisory strength Santa Ana winds below the Cajon Pass and
the Santa Ana canyons Sun night/Mon...
More record heat on tap for Mon/Tue...
Chance for some light showers Thursday...
Skies were sunny across Southern California at midday...but
satellite imagery showed a large are of marine clouds/fog along the
o.C. Coast and extending SW across a large portion of the bight. It
was noticeably cooler west of the mts at midday thanks to a shallow
marine layer. Dewpoints have surged along the coast and locally
inland which will set the stage for possible fog development
overnight. Surface pressure gradients had weak onshore trends...and
at noon...winds were generally light.
With dewpoints surging inland and light winds and mostly clear skies
overnight. Some fog is likely to move back inland or reform and my
be dense...especially along the coast. Any fog that does form will
burn off Sunday morning as offshore flow increases leaving a sunny
and warmer day.
A weak low pressure trough in the upper atmosphere is moving over
California today and will slip south of the region overnight as the
high pressure ridge off the coast builds east. Once again...500h
will exceed 582 dm over southern parts of the state Monday/Tuesday setting
the stage for more record high temperatures. As a matter of fact...
San Diego is on track for the warmest February on record...and given
the persistence of the ridging over the eastpac...we may well break
The main weather concerns will be for areas of dense fog...possibly
as early as this evening and overnight...and increasing offshore
flow Sunday night into Monday. Advisory strength winds are likely...
particularly below the Cajon Pass...and near the Santa Ana mts.
The incoming trough for Thursday continues to look weak. It is moving
through the ridge and forecast to weaken as it moves onshore. This
pattern frequently looks like showers several days out...then
becomes increasingly dry with most of the energy passing to the
north. In any case...both the Gem/European model (ecmwf) are holding onto decent
height falls across socal with a period of light precipitation on Thursday. The
GFS carries most of the energy and precipitation to the north of the
region. Chance probability of precipitation are in the forecast to cover this event.
Following the trough...a fairly zonal pattern sets up for dry and
seasonally mild weather until next weekend when another ridge
emerges over the southwest for more warm and dry weather. The
extended GFS run looks dry through the end of the month as well.
132110z...coast...through 14/0000 UTC...primarily unrestricted visible
and few-scattered clouds at or above 20000 feet mean sea level...except for local dense fog
along the central and northern beaches of Orange County. 14/0000-
0900 UTC...dense fog/low stratus gradually re-developing 5-10
sm...and locally 15 sm...inland...with bases 100-600 feet mean sea level...tops
300-800 feet mean sea level and areas of visible 1/4sm or less. These conditions
continuing through 14/1600 UTC. Confidence in ksan...kcrq and ksna
being impacted with dense fog at times is high...with moderate
confidence in timing.
Valleys/mtns/deserts...unrestricted visible and few-scattered clouds at or above 20000
feet mean sea level through Sunday morning.
110 PM...patches of fog will continue over the coastal waters this
afternoon. Then more widespread dense fog is likely to re-develop
tonight into middle-Sunday morning. A marine weather statement remains
posted. Also...a large west-northwest swell may create combined seas
at 9-10 feet over portions of the outer waters south of San Clemente
Island today...with a dominant period of around 18 seconds. No
hazardous marine weather is expected Sunday afternoon through
110 PM...latest buoy observations from San Clemente basin buoy show
wave heights/periods from the west-northwest of 10 feet/17 seconds...
while nearshore buoys show 6-7 feet/15-18 seconds. Thus...it appears
that the swell is peaking. This long-period swell west-northwest
swell from 290 degrees will continue at around this level today and
then lower during the day Sunday. Expect strong rip currents and
high surf of 5 to 8 feet to continue through Sunday...with highest
surf north of Newport Beach and south of del Mar. A high surf
advisory remains in effect through 8 PM Sunday. The swell and surf
will continue to lower Monday.
Fire weather... weak onshore flow this evening...will begin to turn
offshore on Sunday...then strengthen Sunday night into Monday
forcing very dry air back over the coastal plain through Tuesday.
Strongest winds are expected below the Cajon Pass...and through and
below the Santa Ana mts...but areas below the San Gorgonio Pass and
in the wind-prone coastal foothills of the San Diego County mts will
see locally strong gusts as well...and very low minimum relative humidity Monday
through Tuesday. Models indicate several hours of critical or near-
critical fire weather conditions are possible from just below the
Cajon Pass...through inland Orange County Monday afternoon.
Northeast winds of 15 to 30 miles per hour are likely along the coastal
foothills late nights and mornings through Tuesday...but local gusts
of 45 to around 50 miles per hour are possible late Sunday night through Monday
morning below the Cajon Pass and near the Santa Ana mts. Lowest
inland humidity of 10-15 percent is expected both Mon/Tue...then
increasing on Wednesday as onshore flow develops.
No fire weather products are expected at this time due to marginal
fuel conditions...and the limited number of hours forecast at
California...high surf advisory until 8 PM PST Sunday for Orange County
coastal areas-San Diego County coastal areas.