textproduct: San Diego

SYNOPSIS

Scattered showers are expected to develop today. Rain will become heavy at times late tonight with heavy rainfall from a strengthening atmospheric river spreading southward across the area for late tonight into Wednesday morning with the heavy rain continuing into Wednesday evening. Showers will continue on Thursday with another round of more widespread showers for Thursday night into Friday. Gusty south winds will develop tonight and continue through Wednesday evening with gusts to 40 mph near the coast and to 50 to 70 mph, locally to 80 mph along and below the desert slopes of the San Bernardino County mountains. Snow levels above 9000 feet for Wednesday will fall to around 7000 feet on Thursday to around 5000 feet for early Saturday. Drier weather is expected for the weekend with high temperatures around 5 degrees below average.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

AVIATION

231800Z....A high broken to overcast layer of clouds will continue to cover the area around 20-25k ft MSL through the TAF period. Low clouds with bases 1500-5000 ft MSL expected along the coast with inland areas getting as low as 300-700ft MSL after 12-14Z Wednesday. Light rain chances through the day today with increasing chances through this evening and overnight. Vis reductions 1-4 SM are expected as rain chances increase. The main rain band will move in from the northwest to the southeast towards the end of the TAF period and will bringing moderate to heavy precipitation with vis reductions 1-3 SM along with strong south to SE winds.

MARINE

An approaching storm system will lead to strengthening south to southeast winds and building seas this afternoon. Winds initially around 15-20 kts gusting to 25 kts this afternoon will increase early Wednesday to gale force, with wind gusts upwards of 35 kts. This will bring steep combined seas of 6-9 feet. Additionally, periods of moderate to heavy rain Wednesday will lead to areas of poor visibility. Winds diminish slightly late Wednesday through early Thursday, but winds and seas will remain hazardous to small craft. Another round of stronger southwest winds expected late Thursday into early Friday, with gusts around 25 kts. Winds weaken and turn northwesterly Friday.

HYDROLOGY

Scattered, mostly light showers are expected to develop today and continue into this evening. Rain is expected to become heavy at times late tonight along the south slopes of the San Bernardino County mountains with heavy rainfall spreading southward across the area for late tonight through Wednesday morning with the heavy rainfall continuing through Wednesday evening. Showers will continue on Thursday with another round of more widespread showers for Thursday night into Friday. The snow level will rise to above 9000 feet for early Wednesday morning, fall to around 7000 feet on Thursday and Thursday night, then fall to 4500 to 5000 feet for early Saturday morning.

Through Wednesday night, for Orange and southwestern San Bernardino Counties, rainfall could range from 2.5 to 3.5 inches near the coast to 6 to 8 inches on the coastal slopes of the San Bernardino County mountains with isolated totals to around 12 inches on the coastal slopes to the west of the Cajon Pass. Rainfall will decrease from north to south with rainfall across far southern San Diego County around 1.5 inch near the coast to 2.5 inches in the mountains. For the high desert, 1.5 inch to 3.5 inches near the foothills of the San Gabriel Mountains is expected with 0.75 to 1.5 inch for the lower deserts.

The San Bernardino County mountains are part of a high risk area for excessive rainfall for Wednesday morning through Wednesday night, areas with a heightened risk for damaging and potentially life-threatening flash flooding. Hourly rainfall rates of around 0.50 inch are likely for several hours on the coastal slopes of the eastern San Gabriel Mountains from before dawn on Wednesday through Wednesday afternoon, locally to around 1 inch per hour from thunderstorms or bands of heavier showers.

Additional rainfall during the day on Thursday from showers will range from around 0.50 inch north to 0.25 inch south, locally to around 1 inch on the coastal slopes of the San Bernardino County mountains.

For Thursday night and Friday, a weaker atmospheric river will bring another round of more widespread showers with a slight chance of thunderstorms. For Orange and southwestern San Bernardino Counties, rainfall could range from around 0.75 inch near the coast to 1 to 2 inches on the coastal slopes of the San Bernardino County mountains with isolated totals to around 3 inches on the coastal slopes to the west of the Cajon Pass. Rainfall will decrease from north to south with rainfall across far southern San Diego County around 0.25 to 0.50 inch. For the high desert, 0.25 to 0.50 inch is expected with less than 0.25 inch for the lower deserts.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...High Surf Advisory from 11 PM this evening to 11 AM PST Saturday for Orange County Coastal Areas-San Diego County Coastal Areas.

Wind Advisory from 3 AM to 10 PM PST Wednesday for Orange County Coastal Areas-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Coastal Areas-San Diego County Valleys-Santa Ana Mountains and Foothills.

Flood Watch from late tonight through late Wednesday night for San Diego County Coastal Areas-San Diego County Deserts-San Diego County Mountains-San Diego County Valleys.

Flood Watch from this evening through Wednesday evening for Apple and Lucerne Valleys-Coachella Valley-Orange County Coastal Areas-Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Gorgonio Pass near Banning-Santa Ana Mountains and Foothills.

High Wind Warning until 3 PM PST Thursday for Apple and Lucerne Valleys-San Bernardino County Mountains.

PZ...Gale Warning from 1 PM this afternoon to 4 PM PST Wednesday for Coastal Waters from San Mateo Point to the Mexican Border and out to 10 nm-Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.