Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
116 PM PST Thursday Nov 27 2014
the weather will begin to change on Friday as the offshore flow ends
weakens and the sea breeze returns...spreading higher humidity
inland. There will also be a return of night and morning coastal low
clouds and fog. Low pressure over the eastern Pacific is expected to
begin to spread a deeper moist layer over California sometime next
week. Timing is uncertain...but expect more clouds and a chance of
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Record warmth for Thanksgiving in San Diego
Still no certainty on arrival/amounts of rainfall next week
It was a sunny and very warm Thanksgiving over socal this afternoon.
We gobbled up the old record high of 83 degrees established at
Lindbergh Field back in 1903 with a new record 85 degrees at noon.
There may be more before the day is over. At midday...surface
pressure gradients were still running around 8 mbs offshore from
Nevada...and 1-2 mbs offshore from the lower deserts. The offshore
gradients were still supporting easterly wind gusts as high as 30
miles per hour...but generally winds speeds were 15 miles per hour or less. Relative humidity values were
extremely low at 6-12 percent.
Today should be the peak of the heat west of the mountains as easterly
winds subside. Lighter winds will prevail on Friday as gradients turn
back onshore...bringing welcome marine air back to coastal areas. It
will be cooler as well...but still well above average inland. Skies
will be fair through Friday...then look for an increase of marine
clouds and fog Friday night into Sat morning.
Weather concerns in the near term...other than the extreme dryness
and elevated wildfire threat today...there is a chance of some dense
fog along the coast Friday night/Sat morning. After that...an eddy
should prop up the marine layer and associated clouds/fog. This
would keep any dense fog threat farther inland and elevation
The strong ridge of high pressure overhead will slowly cave into the
weekend. This will allow surface pressure to fall over the Great Basin
and bring a broad return of onshore flow across California. Rain will
develop across northern portions of the state as a plume of high precipitable water
air interacts with waves of low pressure spun off of a large area of
low pressure covering the eastpac. This feature may eventually bring
rain to southern portions of the state next week...but the various
global model solutions handle this complicated situation very
differently...so timing and amounts of precipitation this far south are
uncertain at best.
The general trend of the medium range guidance with GFS/ECMWF/Gem
are to slow down the eastpac system. The European model (ecmwf) runs are the slowest.
On Monday 18z...the 12z run has a cut-off low near 33n/138w (well
offshore) while the 12z GFS has it some 400 nm farther NE. The 12z
Gem is close to the 12z ec solution. The 12z GFS operational/
parallel runs have slowed the system a bit from the 06z run...but
keep it progressive and are by far the most aggressive bringing
precipitation to socal later on Tuesday. There is also some interaction of the
subtropical jet and associated deeper moisture that may enhance
rainfall when the system eventually moves inland.
Based on these disparate solutions...uncertainty reigns supreme with
regard to storm effects on socal next week. For now...we will have
slight chance/chance probability of precipitation for the Sunday period as a shortwave
traverses the area. This would be more of a light...stratiform event
with the greatest amounts on the coastal slopes. Model consensus is
to delay arrival of any significant precipitation associated with low
pressure off the coast until after Tuesday morning...but if the latest
European model (ecmwf)/Gem solutions are correct it would be delayed even further and
diminished with the brunt of the moisture coming inland over
northern California. Probability of precipitation have been reduced accordingly for the later
periods and grids currently reflect a blend of the more aggressive
GFS solutions and the minimal European model (ecmwf) with more clouds through midweek.
272100z...VFR conditions with few/scattered high clouds through Friday.
100 PM...no hazardous marine weather is expected through Sunday.
Isolated showers ahead of a storm system could develop over the
coastal waters Monday.
extremely low relative humidity...daytime temperatures climbing into the 80s to
lower 90s...and locally gusty easterly winds along the foothills...
will continue elevated fire weather conditions through this
Expect some improvement on Friday as the offshore weakens and the sea
breeze develops. There will be some return of moisture along the
coastal strip...but inland...minimum relative humidity will remain below 15
percent. Better recovery on Saturday as onshore flow strengthens.