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.

SHORT TERM (Today through Christmas)

A low pressure system well off the southern California coast will rapidly intensify on Wednesday and Wednesday night with a surface low with a pressure around 980 mb moving northward to a position off the coast of northern California. Satellite imagery shows a band of moisture extending northward from this area of development into the northern California coast.

There have also been widespread thunderstorms overnight well to the south of the southern tip of Baja around 15N/110W. Moisture from this area is spreading northward into portions of southern California. As the low pressure system off the California coast intensifies and taps the subtropical moisture to the south, values of Integrated Vapor Transport in an intensifying atmospheric river will increase to around 1000 kg/m/s near the southern California coast on Wednesday.

Winds across southwestern California will strengthen for late tonight into Wednesday evening with gusts to 40 mph near the coast and to 55 to 75 mph along the desert slopes of the San Bernardino County mountains into the adjacent desert areas.

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.

LONG TERM (Thursday night through Monday)

Another round of more widespread showers is expected for Thursday night into Friday. This system will have moisture from a weaker atmospheric river with Integrated Vapor Transport values increasing to around 500 kg/m/s near the southern California coast for late Thursday night into Friday morning.

Drier weather is expected for the weekend with high temperatures a few to around 5 degrees below average. High temperatures on Sunday will range from the 60s for the coast, valleys, and lower deserts to the 40s and lower 50s in the mountains.

AVIATION

231100Z....BKN-OVC high clouds will continue to stream over the region. Low clouds based 400 to 1100 ft MSL with tops to 1500 ft MSL along the coast early this morning will gradually rise to 1200-1800 ft MSL by 12-16Z, with accompanying improvements in vis along coastal areas and reductions for higher inland terrain as clouds spread into inland valleys.

Iso-sct DZ/-SHRA possible starting 15Z this morning and continuing through the rest of today, which will locally lower cigs/vis, especially for mtn foothills. Low clouds will continue to rise late morning, with periodic clearing in the valleys 17-20Z before widespread clouds return across the region through the rest of the period based 2500-4000 ft MSL. Breezy south winds will pick up towards 19Z this morning, with gusts to about 20 kt along the coast and to 25-35 kts over higher ridges into parts of the high desert. Occasional updrafts/downdrafts for the leeward side over the high deserts. The main band of widespread SHRA will move into the region from the northwest to the southeast starting Wednesday morning, 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.

BEACHES

Strengthening south winds tonight into Wednesday will lead to elevated surf 5 to 8 feet with sets to 9 feet, highest for south- facing beaches. This will lead to hazardous swimming conditions, as well as possibly minor tidal overflow for south-facing beaches from a combination of winds and elevated surf through Wednesday, especially during high tides. Winds diminish along with surf late Wednesday, but more breezy winds along with large fresh swell will lead to surf building again Friday-Saturday. A Surf Advisory is in effect from tonight to Saturday afternoon.

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 from noon today to 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.