Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
935 am PST Wednesday Dec 4 2013
a cold trough of low pressure will remain over the west through this
weekend. Daytime temperatures will be roughly 10 to 20 degrees
below...with frosty conditions possible each night. A few lingering
showers will be possible over mainly the San Diego County mountains
and foothills today...with periods of isolated showers possible over
the mountains through Thursday. A stronger and colder disturbance
will re-enforce the cold air in place and bring a better chance of
precipitation to the region on Saturday. A gradual warming trend
will then develop for next week.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Water vapor imagery shows a very elongated trough of low pressure
over the west this morning...with the associated cold front now
pushing south into Mexico. As a result...colder air is now
filtering into the area...and skies are clearing. Just a few high
clouds remain...along with some cold air cumulus west of the
mountains. The strong onshore pressure gradients of last night are
dropping off quickly this morning...with just a few of the favored
spots still gusting to around 40 miles per hour. Otherwise...current radar
imagery is not showing any shower activity either...so have updated
the forecast this morning to reflect current trends and to expire
the High Wind Warning. Did leave the potential for an isolated
showers over the San Diego County mountains and foothills
today...but even that chance looks relatively remote right now.
Therefore...expect another cool day across the region today...with
temperatures running 5 to 15 degrees below normal and locally up to
20 degrees below normal.
Another disturbance will move through this trough tonight...bringing
another surge of cold air to Southern California. The moisture will
be extremely limited...and models right now are only hinting at a
few showers developing late tonight over the coastal slopes...and
once again favoring San Diego County at that. Therefore...think the
primary threat tonight will be with frosty conditions developing
across the inland valleys and some of the colder drainage coastal
locations. Therefore...frost advisories will likely be needed with
the afternoon package for at least the inland Empire. The High
Desert will also see temperatures falling below freezing mark...but
given that they have already had a handful of frosty or freezing
nights will likely hold off issuing a freeze warning for them.
These cool day time and cold overnight conditions will then continue
into Thursday and Friday...with only minor fluctuations in
The real focus of the forecast then turns to Saturday...as the
models continue to indicate a stronger and colder disturbance diving
south through the trough. The models initially give this system a
slightly more over water trajectory before cutting it inland across
central California...so it appears that there will be more moisture
to work with...even given the cold air in place. There will also be
good upper level level jet support as well as another surge of the
modified polar airmass. Therefore...think that the showers will
likely start late Friday night along and west of the mountains...but
the brunt of the moisture will move across the region on Saturday.
Snow levels will also be quite low with this system...likely around
3000 feet...and potentially as low as 2500 feet. Although showers
will linger into Saturday night...drier conditions will start to
develop...with another cold day prevailing on Sunday.
A gradual drying and warming trend will then develop for the first
part of next week...as high pressure tries to build back across the
041630z...bkn-ovc cloud layers between 3000-4000 feet and tops around
5000 feet mean sea level will continue through the remainder of the day in San
Diego County...with visible mainly p6sm. Skies will continue few/scattered
elsewhere. After 05/0600z tonight...the marine layer will deepen
with bases around 3000 feet mean sea level and tops rising to 6000-9000 feet mean sea level.
Light showers will develop over the mountains as well as in many of
the San Diego County coastal and valley areas. Visible will drop to
below 3sm where clouds intersect the terrain. In addition...cloud
bases may lower to 2500 under the rain cores.
Elsewhere...unrestricted visible and few-scattered clouds 4000-15000 feet mean sea level.
the 8 am observations at San Clemente buoy reported winds continuing
to gust to 21 knots. The steep seas and strong winds will create
hazardous boating conditions for small craft. Winds and seas should
improve during the day Thursday. The Small Craft Advisory for the
inner waters will remain in effect for the inner waters through 10
am this morning and outer waters until 10 am Thursday.
Astronomical high tides of 7.3 feet at San Diego will occur during
the middle-morning hours today...creating the small threat of minor
tidal overflow of low lying beach areas during high tide. A beach
hazard statement is in effect through this morning. High tides will
be below 7 feet starting Thursday.
Another trough of low pressure moving into the region Saturday will
bring another round of strong west to northwest winds and steep seas
to the coastal waters...making for hazardous conditions for small
craft once again.
Skywarn activation is not requested. However...weather spotters are
encouraged to report significant weather conditions.
California...beach hazards statement until noon PST today for the Orange
County coastal areas...San Diego County coastal areas.
Pz...Small Craft Advisory until 10 am PST Thursday for the waters
from San Mateo Point to the Mexican border extending 30 to
60 nm out including San Clemente Island.
Small Craft Advisory until 10 am PST this morning for the
coastal waters from San Mateo Point to the Mexican border
and out 30 nm.