Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
855 PM PST Friday Dec 6 2013
an area of low pressure diving southeastward through the Great Basin
will bring rain...snow...and a reinforcing shot of cold air to our
region on Saturday. Snow levels will hover between 3000 and 3500
feet in the mountains...with locally heavy snowfall for higher
elevations. Strong and gusty west winds for the mountains and
deserts are also expected into Saturday night. The storm exits the
area Sunday...leaving US with a period of gusty offshore winds for
the favored passes and canyons on Monday. Otherwise...look for a
gradual warming trend and fair skies through Thursday.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Water vapor loop shows the potent upper level circulation that will
be impacting our area Saturday is currently west of Oregon this
evening. This strong shortwave will move down the California
interior tonight on powerful 130kt 300 mb jet. At 8 PM...the leading
edge of the clouds and precipitation extended from Monterey to
Yosemite National Park. The light showers will begin in socal early
Saturday morning...then increase in coverage and intensity through
midday as the system approaches.
Most of the moisture from this system will come from the 6000 foot
deep marine layer which will limit the precipitation amounts
somewhat. The bulk of the precipitation will fall between 10am and 7pm
Saturday. This is when a narrow band of higher precipitable waters of 0.75" over
the Pacific moves into socal in conjunction with the surface cold
front and strong dynamics aloft. The precipitation will taper off to
showers Saturday evening. The showers will linger longest in the San
Diego County mountains Saturday night.
Precipitation amounts...the high res mesoscale runs show substantial
orographic enhancement with strong low level 850 mb winds of
40-50kts with this system. An inch or more of rain is likely on some
of the coastal slopes below the freezing level. Snow levels will
lower throughout the day and the strong orographics may result in
locally heavy snow on the slopes above 5000 feet. A Winter Storm
Warning is in effect for all higher mountains Sat/Sat night.
Surfacing mountain waves are possible on the eastern mountain slopes
and onto the desert floor. Gusts could exceed 60 miles per hour in these areas.
Continued cool on Sunday with a second upper level trough moving
across socal. This sharp trough will keep the onshore flow in place
and the marine layer will remain fairly deep. The 00z GFS generates
quantitative precipitation forecast over socal Sunday evening with this second shortwave...something
to watch for in successive runs for possible inclusion into the
Long range outlook for next week...on Monday morning a strong
surface high builds over Nevada bringing moderate to potentially
strong offshore flow to the socal mountains through Tuesday.
Advisory strength winds are likely in some areas.
Frost and freeze concerns return early next week when this
cold...dry Continental airmass settles over the southwest. The days
will be cool and the nights will be cold with frost and freezing
temperatures in the wind sheltered valleys each night. The airmass
modifies Wednesday and Thursday for warmer days...but the nights
will remain cold with overnight lows in the upper 20s and low 30s in
the valleys in this very dry airmass.
Another trough drops into the area from the north on Friday and
Saturday bringing our next chance for light precipitation.
070300z...sct/bkn low clouds...with bases 4500-6000 feet and tops to
8000 feet mean sea level...will continue this evening over the mountains and
foothills. -Shra will develop from northwest to southeast tonight through Sat
night...with greatest coverage of showers over and west of the mountains
ceilings will lower to around 2500 feet mean sea level...and visible down to 4-6 sm in
some showers. Snow level will lower to around 3500 feet...with snow
and ice possible at higher elevation aerodromes.
Strong westerly winds will result in mountain wave activity with moderate-strong
uddfs and surface winds gusting to 50-60 knots over the mountains and desert
slopes Sat afternoon...with strong winds reaching the desert floor Sat
night. Winds will diminish Sunday morning.
a low pressure trough traversing across Southern California will
create gusty west to northwest winds to 35 knots...and steep seas to 11
feet in the outer waters Saturday morning through Sunday morning.
Gusty winds and steep seas will combine to create hazardous boating
conditions for small craft. A Small Craft Advisory remains in effect
for both the inner and outer coastal through the period. Rain
showers will also be possible tonight through Sunday morning. Winds
and seas will begin to diminish Sunday morning.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...Winter Storm Warning from 10 am Saturday to 4 am PST Sunday for
the Riverside County mountains...San Bernardino County
mountains...San Diego County mountains.
High Wind Warning from 10 am Saturday to 4 am PST Sunday for the
apple and Lucerne valleys...Coachella Valley...San Diego
Pz...Small Craft Advisory from 8 am Saturday to 8 am PST Sunday for
the waters from San Mateo Point to the Mexican border
extending 30 to 60 nm out including San Clemente Island.
Small Craft Advisory from 8 am Saturday to 3 am PST Sunday for
the coastal waters from San Mateo Point to the Mexican
border and out 30 nm.