textproduct: San Diego

SYNOPSIS

Onshore flow will spread cooling inland through Saturday with night and morning coastal low clouds and fog spreading inland into the far western valleys at times over the weekend. Not much change is expected for Sunday and Monday with high temperatures for inland areas still 10 to 15 degrees above average. A low pressure system from the west will bring increasing chances for rain beginning on Tuesday. Moisture from an atmospheric river will bring increasing chances for widespread heavy rainfall for Wednesday into Thursday with decreasing chances for rain for the final weekend in December.

SHORT TERM (Today through Sunday)

Satellite imagery and surface reports shows widespread low clouds and locally dense fog has returned over the inner coastal waters extending locally inland along the coast. A Dense Fog Advisory continues for areas near the coast in San Diego County through 9 AM this morning and for Orange County from the coast inland to around Interstate 5 through 10 AM this morning.

Night and morning coastal low clouds and fog are expected to spread a little farther inland each night through the weekend as the marine layer slowly deepens. Visibilities won't be as low near the coast with the lower visibilities moving upward and inland to near higher coastal terrain inland to the far western valleys.

Onshore flow will bring cooling of high temperatures for a few to around 5 degrees today for the coast inland to the coastal slopes of the mountains with a few to around 5 degrees of cooling for Saturday for most areas with not much change for Sunday and Monday.

High temperatures for Sunday and Monday will still as much as 10 to 15 degrees above average for inland areas with high temperatures ranging from the mid to upper 60s near the coast to the 70s for the valleys with the lower deserts around 80.

LONG TERM (Monday through Thursday)

A low pressure system from the west will bring increasing chances for rain beginning next Tuesday with moisture from an atmospheric river bring increasing chances for widespread heavy rainfall for Wednesday into Thursday (Christmas Eve and Christmas). High temperatures will cool to around average for Wednesday and Thursday.

For Tuesday night and Wednesday, there could be stronger south to southeast winds across the coastal waters and adjacent coastal areas with the ECMWF Extreme Forecast Index having winds between the 70th and 80th percentile. Please see the Hydrology section below for details on the rainfall potential through Thursday night of next week.

AVIATION

191050Z...Coast...Areas of dense fog and CIGS below 500 ft MSL will continue along the coast and locally up to 10 mi inland through the morning. Confidence is low in fog moving into KCRQ due to weak offshore/easterly flow there, and KSAN vis likely varying between 1/4 SM and 3 SM as they remain on the edge of the fog bank. Fog clearing to the coast 15-18Z, latest in Orange County. Areas of low clouds with bases 400-700 ft MSL spreading back inland after 20/02Z with vis 2-5 SM, locally down to 1/4 SM again on the coastal mesas and higher coastal terrain.

Otherwise...FEW-SCT high clouds with unrestricted VIS through Saturday morning.

MARINE

Areas of dense fog reducing visibility to 1 NM or less this morning, mainly over the inner coastal waters. Visibility will improve by late morning. Otherwise, no hazardous marine conditions are expected through Tuesday morning, then gusty south winds developing Tuesday evening with a Pacific storm. Conditions could become hazardous to small craft at times Tuesday night and Wednesday.

HYDROLOGY

A low pressure system from the west will bring increasing chances for rain beginning next Tuesday. Moisture from an atmospheric river will bring increasing chances for widespread heavy rainfall for Wednesday into Thursday. More than 60 percent of ECMWF members now have values of Integrated Vapor Transport exceeding 750 kg/m/s directed into southwestern California centered during the day on Wednesday with the ECMWF control run having around a 21-hour duration of IVT exceeding 500 kg/m/s and the ECMWF ensemble mean having around an 18-hour duration exceeding 500 kg/m/s.

For Wednesday morning through Wednesday night for Lytle Creek on the coastal slopes of the eastern San Gabriel Mountains, the chance for 3 inches or more of rainfall has increased to 71 percent with a 35 percent chance for 5 inches or more and an 11 percent chance for 6 inches or more. For Wednesday morning through Thursday night, the chance for 8 inches or more of rainfall at Lytle Creek has increased to 13 percent.

NBM deterministic rainfall for next week through Thursday night for northern Orange and southwestern San Bernardino Counties ranges from 3.5 to 4 inches near the coast to 6 to 9 inches on the coastal slopes of the mountains to the west of the Cajon Pass. Amounts decrease to the south to 1.5 to 2 inches near the coast of central and southern San Diego County to 2 to 3 inches for the mountains of central and southern San Diego County. For the high desert, 2 to 3 inches is expected with 0.5 to 1.5 inches for the lower deserts.

Most of the precipitation across southwestern California through Christmas Thursday is expected to fall as rain with snow levels remaining above 7000 feet.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Dense Fog Advisory until 9 AM PST this morning for San Diego County Coastal Areas.

Dense Fog Advisory until 10 AM PST this morning for Orange County Coastal Areas-Orange County Inland Areas.

PZ...None.