Onshore flow will bring cooling to the coast into the valleys today with high temperatures for inland areas still 10 to 15 degrees above average. Lighter rain could develop as early as Tuesday in advance of a low pressure system off the California coast. Heavier rainfall will develop and spread southward across the area Tuesday night and early Wednesday with widespread heavy rainfall for Wednesday and Wednesday night. Gusty south winds will also occur Tuesday night through Wednesday evening with gusts to 40 mph near the coast and to 50 to 70 mph along and below the desert slopes of the San Bernardino County mountains. Showers with locally heavy precipitation could continue for Thursday and Thursday night with decreasing chances for showers through weekend. Snow levels above 9000 feet for Wednesday will fall to around 7000 feet on Thursday to around 5000 feet for early Saturday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Key Points:
* Widespread moderate to heavy rainfall Christmas Eve with the potential for roadway flooding and localized flash flooding from the coast to deserts. Rapid rises in small streams and increased flow in main stem rivers expected. 27 percent chance of the San Diego River reaching minor flood stage.
* Snow levels are forecast to remain above 8000 feet into Christmas morning, increasing potential for rock and mudslides along mountain highways, and debris flows in and below burn scars, especially in the San Bernardino County mountains.
* Gusty southerly winds are expected across the area with 70-90 percent chance of wind gusts exceeding 35 mph along the coast Tuesday night into Wednesday. Make sure to secure outdoor furniture. Tree damage is possible.
* Additional chances of showers Thursday through Sunday. Snow levels are expected to lower to 6500 to 7000 feet by Friday morning, creating slick conditions on mountain highways.
(today through Wednesday), Satellite imagery shows coastal low clouds extending inland into the western valleys early this morning with surface reports generally showing the lowest visibilities in fog in San Diego County near higher coastal terrain into the western valleys with the lowest visibilities in Orange County generally from near the coast inland to around Interstate 5. A Dense Fog Advisory is in effect for these areas through 10 AM this morning.
Onshore flow will bring cooling for the coast into the valleys today with high temperatures for inland areas still 10 to 15 degrees above average. High temperatures for today will range from the lower to mid 60s near the coast to the 70s for the Inland Empire with the mid to upper 70s for the lower deserts.
Lighter rain could develop as early as Tuesday in advance of a low pressure system off the California coast. Heavier rainfall will develop and spread southward across the area Tuesday night and early Wednesday with widespread heavy rainfall for Wednesday morning through Wednesday evening.
Ensemble support for heavier rainfall with greater amounts and less spread among ensemble members is greatest for Orange and southwestern San Bernardino Counties with decreasing amounts and increasing spread going from north to south across San Diego County.
Gusty south winds will develop Tuesday night and continue through Wednesday evening with gusts to 40 mph near the coast and to 50 to 70 mph along and below the desert slopes of the San Bernardino County mountains.
(Thursday through Sunday), The greatest chances for additional precipitation will be for Thursday and Friday, though with increasing spread in potential amounts. There is not much overlap among the members of each of the ECMWF, GFS, and Canadian model ensemble systems. This would usually imply greater uncertainty, at least in the details. While chances for measurable precipitation each day for Saturday into early next week decrease to around 15 to 25 percent, there remain at least small chances for heavier amounts.
Lighter rain could develop as early as Tuesday in advance of a low pressure system off the California coast. Heavier rainfall will develop and spread southward across the area Tuesday night and early Wednesday with widespread heavy rainfall for Wednesday morning through Wednesday evening. Showers will continue for late Wednesday night through Thursday night, but with additional precipitation amounts not as heavy.
Through Wednesday evening, for Orange and southwestern San Bernardino Counties, rainfall could range from 3 to 3.5 inches near the coast to 4 to 6 inches on the coastal slopes of the San Bernardino County mountains with isolated totals exceeding 8 inches. This will decrease from north to south with around 2 inches across far southern San Diego County. For the high desert, 2 to 3 inches is expected with 0.75 to 1.5 inch for the lower deserts.
For late Wednesday night through Friday afternoon for Orange and southwestern San Bernardino Counties, additional rainfall and liquid equivalent above the snow level for Orange and southwestern San Bernardino Counties could range from around 1 inch near the coast to 1.5 to 2.5 inches on the coastal slopes of the San Bernardino County mountains. This will decrease from north to south with around one-quarter to one-half inch across far southern San Diego County. For the high desert, one-quarter to one-half inch is expected with one-quarter inch or less for the lower deserts.
Through Wednesday night for Lytle Creek in the San Gabriel Mountains to the west of the Cajon Pass, the chance for 5 inches or more of rainfall is 85 percent with the chance for 8 inches or more of rainfall 22 percent.
Through Wednesday night for southwestern California, chances for 2 inches or more of rainfall range from 90 to 100 percent for the coast to the mountains for areas bordering Los Angeles County to 25 to 35 percent across far southern San Diego County.
Snow levels will rise above 9000 feet on Wednesday morning, then fall to around 7000 feet on Thursday and 5000 feet for early Saturday.
221030z. Coast/Valleys, Patchy low clouds based 400-800 ft MSL with tops to 900 ft are present from the coast to 15-20 miles inland. Widespread vis restrictions 2-6 SM in BR, 0-2 SM where clouds intersect with higher inland terrain, will continue overnight. Occasional scatter outs will continue as high cloud layer occasionally disrupts the low clouds, with fuller clearing to the coast 17-20Z. Low clouds will linger along the immediate coast in areas through the afternoon, before moving back onshore after 23/00Z. Bases initially 700-1200 ft MSL will steadily rise overnight, likely to above 2000 ft MSL by 23/12Z, and clouds will spread to cover the coastal basin. Areas of DZ early Tues morning will locally lower cigs/vis.
Otherwise, SCT-BKN high clouds with unrestricted VIS continues through today.
No hazardous marine conditions through Tuesday morning. An approaching storm system will lead to strengthening winds and building seas starting Tuesday afternoon. Winds initially 15 to 20 knots gusting to 25 knots Tuesday afternoon will strengthen further late Tuesday night, potentially to gale force with wind gusts upwards of 30-35 knots. This will bring steep seas 7-10 feet. Additionally, periods of moderate to heavy rain Wednesday will lead to areas of poor visibility. Strong winds and steep seas continue through early Thursday morning. Winds weaken slightly Thursday morning, but likely remain hazardous to small craft through most of the day. Winds weaken and turn northwesterly Friday.
Ca, Flood Watch from late Tuesday night 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 Tuesday afternoon 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.
PZ, Gale Watch from Tuesday afternoon through Wednesday afternoon 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.
