Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 101648
Area Forecast Discussion
National Weather Service San Diego CA
848 AM PST Sat Dec 10 2016
A weak shortwave trough passing by to the north, will bring stronger
onshore flow with high clouds, a deeper marine layer, and possible
scattered showers late tonight into Sunday west of the mountains.
Gusty westerly winds will develop over the higher mountains and upper
deserts tonight. Dry and seasonal for the first half of next week
under weak high pressure aloft. Toward the end of next week, a cold
low pressure trough will develop over the West, bringing much cooler
weather, periods of showers, and gusty westerly winds over the
mountains and deserts.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Early satellite imagery shows extensive marine stratus covering all
of O.C. and western San Diego Counties, beneath patchy cirrus clouds.
The 12Z Miramar sounding had a 5.5 degree C inversion based near 1540
FT. Another weak inversion was near 5600 FT. At 8 AM PST...Ridge top
winds were locally 20-30 MPH, otherwise winds were generally light.
Expect a mix of clouds today with limited sun west of the mountains.
No changes to the forecast at this time.
From Previous Discussion...
.SHORT TERM (Today through Monday)...
Strong...nearly zonal flow will continue across the eastern
Pacific into the western states. A weak trough of low pressure
will move inland to the north today and into the Great Basin
tonight. This will strengthen the onshore flow across Southern
California. The marine layer has deepened to around 2000 feet
early this morning with coastal stratus pushing into portions of
the western valleys with patchy dense fog at Ramona and Chino. The
marine layer will continue to deepen onto the lower coastal
mountain slopes for tonight into Sunday. The increasing onshore
flow...increasing precipitable water...and the deepening of the
marine layer may be sufficient for a few light showers along and
west of the mountains late tonight into Sunday morning. The
stronger onshore flow will bring strong gusty west winds for the
mountains and upper deserts tonight with the strongest winds near
the mountain ridge tops onto the desert mountain slopes where
winds could be near advisory strength with gusts to 50 mph and
isolated gusts to 60 mph. A little weaker onshore flow and weaker
winds for Sunday into Monday.
.LONG TERM (Tuesday through Friday)...
A little warmer for Tuesday under weak high pressure. Later in the
week into next weekend...a cold low pressure system may develop in
the vicinity of California with continuing differences among the
global models with the details. This would bring much cooler
temperatures with periods of showers and periods of strong gusty
west winds in the mountains and deserts. Much lower snow levels
are possible...possibly down to around 3500 feet on Friday night
and Saturday...low enough to impact travel through the Cajon Pass.
101610Z...OVC-BKN stratus 20-40 sm inland with bases 1000-1600 ft
msl, tops around 2100-2500 ft msl, areas of vis 3-5 sm, and local
vis AOB 1/4-2 sm, will likely partially clear and lift through 2000
UTC, with unrestricted vis and BKN clouds AOA 20000 ft msl
elsewhere. Marine layer inversion strength of 5 deg C this morning.
2000-11/0000 UTC...SCT-FEW clouds 1500-3000 ft msl in the coast and
valleys and local vis 3-5 sm HZ in the valleys, with otherwise
mainly unrestricted vis and BKN clouds AOA 20000 ft msl continuing
all areas. 11/0000-1500 UTC...OVC clouds developing in the coast and
valleys and spreading into the mountain passes and coastal slopes,
with bases around 1500-3000 ft msl, tops 3500-4500 ft msl, and
mountain obscuration of lower coastal slopes. -DZ and/or a few -SHRA
may develop over and west of the mountains after 11/0600 UTC.
After 11/0000 UTC...W winds 15-25 kt with gusts 35-40 kt over
mountain ridges, through/below passes/canyons, along desert slopes
and into adjacent desert areas will create mod-stg uddfs/llws over
and E of the mountains.
Brief gusts to 20 knots possible this afternoon and evening mainly
in the outer waters. Otherwise, no hazardous marine weather is
expected through Wednesday.
Morning high tides will reach 6.7-7 feet Monday through Thursday,
but surf and swells are expected to be on the smaller side, so any
tidal overflow threat will likely be small.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.