Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
853 PM PST Wednesday Nov 25 2015
a cold and nearly stationary low pressure system over the Great
Basin will continue cool weather with periods of scattered showers
across Southern California through the Thanksgiving Holiday
weekend. Warmer early next week as the low moves east.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Minor changes to the forecast to classify near-term probability of precipitation in terms of
coverage instead of probability.
Satellite imagery this evening showed areas of marine clouds
covering much of the California bight...and some lingering clouds inland
over the mts. Radar had scattered very light showers developing over
the coastal waters and drifting slowly inland. No amounts have
been recorded in the past few hours. The 00z Miramar sounding had a
steep lapse rate in the lowest one mile...topped by a weak 1.5
degree c inversion based near 6k feet. Precipitable water was just below one-half inch.
At 8 PM PST...surface pressure gradients were running 2-4 mbs
onshore...helping to fuel peak wind gusts of 35-45 miles per hour along the
windier mountain ridges.
Given the steep lapse rate below 800 mbs and weak onshore flow...
expect isolated/scattered showers will continue to develop overnight and
drift inland with minor precipitation amounts along and west of the mts.
Friday still looks more favorable for greater precipitation amounts with
moderately low snow levels...but models are not very bullish with
quantitative precipitation forecast...except for the 12z cansac WRF run. Would like to see more
models jump on board with the greater quantitative precipitation forecast amounts as depicted on the
cansac WRF before cranking up probability of precipitation further. But the upper air
pattern and cold air aloft support some precipitation here on Friday.
From previous discussion....
The deep closed lower over the Great Basin will bring below average
temperature through the weekend. 500 mb vorticity maxima rotating
around the Great Basin low will track across so-cal at time to bring
a few additional periods of mainly light showers through Friday.
Most of the time it will be dry but there are a few periods where
precipitation chances will be enhanced by these weak impulses aloft. The
first vorticity maximum is weak and arrives Thursday for small chances of
light rain and mountain snow. A second...stronger wave on Friday holds
better chances for more appreciable precipiation. Rain chances will
generally be greater over San Diego County and less to the north.
Snow levels will hover between 4500 to 5500 feet through Friday with
the lowest snow levels over the San Bernardino and Riverside County
Saturday through Tuesday...
over the weekend the Great Basin low fills and slowly begins to
drift northeast. Both the GFS and European model (ecmwf) forecast brief ridging
Monday for dry...warmer weather before the next upstream shortwave
moves inland across California Tuesday for minor cooling and a few
In the tropics: the hurricane season comes to a close on November
30th and is going out with a bang. Hurricane Sandra is the
strongest hurricane so late in the season in the eastern Pacific. It
is a category 3 (major) hurricane and could strengthen further
tonight and Thursday. Sandra poses no threat to Southern
California...but moisture from Sandra will drift across Mexico and
into the Southern Plains this weekend where heavy rain is forecast.
Aviation... 260500z...sct/bkn clouds will continue over most areas
from the mountains west to the coast through at least Thursday night with
scattered showers at times. Ceilings will be variable...2500-6000 feet mean sea level
and tops to 9000 feet mean sea level...with occasional MVFR ceilings below 3000 feet
above ground level at some airports mainly through 17z Thursday and then again Thursday
night. Coastal mountain slopes and ridges will be obscured in
clouds/fog at times. Local surface wind gusts from the west 30-40 knots
will occur on Desert Mountain slopes and through San Gorgonio Pass
through 15z Thursday...then decrease.
Marine... 900 PM...winds will gradually decrease overnight...though
some gusts between 20 and 25 knots are still likely the next few
hours. A Small Craft Advisory remains in effect for the outer and
inner waters through 3am Thursday. Isolated showers are possible at
times through Friday. Conditions will improve this weekend.
Beaches... 900 PM...astronomical high tides will reach at least 7
feet each morning through Friday. Predicted highest tides along the
open coast of San Diego and Orange counties will be:
Thursday: 7.5 feet at 831 am PST friday: 7.3 feet at 912 am PST
There is a threat of minor coastal flooding through Friday during
morning high tides. Elevated surf of 3 to 4 feet and breezy onshore
winds could add to the flooding threat...especially with the morning
high tides. A coastal Flood Advisory remains in effect for coastal
Orange and San Diego counties through noon Friday. Strong rip
currents will likely develop with the elevated surf today and during
the transition from high to low tide each morning. Conditions will
improve this weekend.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...coastal Flood Advisory until noon PST Friday for Orange County
coastal areas-San Diego County coastal areas.
Pz...Small Craft Advisory until 3 am PST Thursday for coastal waters
from San Mateo Point to the Mexican border and out to 30 nm-
waters from San Mateo Point to the Mexican border extending
30 to 60 nm out including San Clemente Island.