textproduct: San Diego

SYNOPSIS

Onshore flow will begin to spread cooling inland today with a return of coastal low clouds and fog likely for tonight into Tuesday morning. A low pressure system from the north will bring greater cooling for Wednesday and Thursday along with showers and a chance of thunderstorms, most likely for Wednesday night through Thursday afternoon. Then dry and warmer for next weekend.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

This afternoon...The inland areas, mountains and deserts are a few degrees warmer than at this time yesterday while the coastal areas are a few degrees cooler as onshore flow and a sea breeze begin to spread marine air inland. Skies are clear except for a few low clouds that formed over the coastal waters early this morning.

Onshore flow ahead of a low pressure system approaching from the northwest will help to spread the low clouds into the coastal areas tonight. Initially, the clouds will be very low and there is a chance of locally dense fog on elevated coastal terrain. A developing coastal eddy, cyclonic flow aloft and falling heights will cause the marine layer to deepen and the clouds to lift overnight into Tuesday morning.

We can expect a general cooling trend through Thursday as the low pressure system moves into SoCal. Thursday will likely be the coolest day, with temperatures from a few degrees to as much a 15 degrees below normal. Ahead of the system, moisture from the low latitudes will likely be drawn into socal with the flow aloft. The system will use this moisture to produce light precipitation as early as Wednesday morning. Precipitation will become more widespread, progressing from northwest to southeast across the region and increasing in intensity on Thursday as the system moves through Socal. Conditions become most unstable on Thursday as colder air moves in aloft from the northwest bringing a chance for thunderstorms for Thursday morning through Thursday afternoon. Precipitation will taper off by Friday morning as the upper level trough axis moves east and conditions become more stable.

For Orange and southwestern San Bernardino Counties, rainfall could range from around 1 inch for the Orange County coastal plain to around 1.5 inches on the coastal slopes of the mountains with amounts decreasing from north to south into San Diego County. For the 24 hr period ending at 5 pm Thursday, there is a 35 to 65 percent chance of greater than 1 inch of rainfall in San Diego County from the coast to the mountains. There is about a 30 to 45 percent chance of 1 inch or more in the Inland Empire and about a 45 to 65 percent chance in Orange County, the Santa Ana Mountains and on the slopes of the San Bernardino Mountains.

The snow level will drop to around 8,000 ft on Thursday afternoon and the highest peaks of the San Bernardino and San Jacinto mountains could get small amounts of snow.

The low pressure system will also bring periods of gusty southwest to west winds in the mountains and deserts for Tuesday through Thursday. Winds will likely be strongest on Thursday and gusts of up to 40 mph could occur in the wind-prone locations.

Dry and warmer weather will return for the weekend under high pressure aloft, with temperatures just below normal inland and just above normal in the coastal areas.

AVIATION

191700Z...Coast...VFR and SKC through late this evening. Low clouds and fog much more likely to form after 05Z Tuesday, becoming more widespread by 12Z Tuesday. Bases would be around 500-800 feet MSL with vis 1-6SM on mesas and higher coastal terrain initially, with bases and vis likely rising slightly Tue morning before clouds scatter out 16-17Z.

Otherwise...Mostly clear and VFR conditions except for SCT-BKN cumulus based around 10 kft over mountains 19-00Z.

MARINE

No hazardous marine conditions are expected through Wednesday morning. A storm system moves into the region later Wednesday through Thursday, bringing gusts at or exceeding 20 knots and associated choppy seas, along with a 10-15% chance of TSRA.

BEACHES

Southerly swells will continue to bring surf of 3 to 6 feet with local sets to 7 feet, highest at south and southwest-facing beaches through Tuesday. This will bring hazardous swimming conditions for most. While surf and rip currents will be elevated, daily high tides will not be particularly high, and the threat of coastal flooding is minimal. Further details can be found in the Beach Hazards Statement.

SKYWARN

Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions.

SGX WATCHES/WARNINGS/ADVISORIES

CA...Beach Hazards Statement through Tuesday evening for Orange County Coastal Areas-San Diego County Coastal Areas.

PZ...None.