textproduct: San Diego

SYNOPSIS

Through Sunday, weak onshore flow and a slowly deepening marine layer will spread cooling inland, but with Sunday high temperatures still 12 to 18 degrees above average for the inland valleys and lower coastal slopes of the mountains. Night and morning coastal low clouds and fog will spread farther into coastal areas early Sunday and possibly into the far western valleys for early Sunday as the marine layer deepens. Fog will be dense near the coast this morning. For Monday into Tuesday, there will be weak offshore flow with inland drying. For Wednesday, stronger onshore flow will spread cooling of around 5 degrees inland with not much change on Thursday.

SHORT TERM (Today through Sunday)

Through the weekend, high pressure aloft will slowly weaken and weak onshore flow with slow deepening of a shallow marine layer will spread cooling inland, but with Sunday high temperatures will as much as 12 to 18 degrees above average for portions of the inland valleys and lower coastal slopes of the mountains. High temperatures on Sunday will range from around 70 near the coast to the mid 70s to lower 80s for the valleys and inland Orange County with the lower 80s for the lower deserts.

Satellite imagery shows widespread low clouds and dense fog over the coastal water extending locally inland along the coast in southern San Diego County and far northwestern Orange County. A Dense Fog Advisory continues for coastal areas until 9 AM. The dense fog is mostly expected to remain below higher coastal terrain such as the mesas in San Diego County. As the marine layer slowly deepens, the low clouds and fog are expected to cover more of the coastal areas for tonight into Saturday morning and might spread into the far western valleys for Saturday night into Sunday morning.

LONG TERM (Monday through Thursday)

Lower level flow will turn weakly offshore for Monday into Tuesday with warming and inland drying on Monday and slight cooling on Tuesday. Stronger onshore flow on Wednesday will spread cooling inland with high temperatures around 5 degrees cooler than Tuesday with additional slight cooling on Thursday.

For the middle and latter part of next week, cluster analysis continues to show the primary forecast variance is in the strength of the high pressure along the West Coast. Those that are weaker with high pressure aloft and stronger with onshore lower- level flow for southern California are more heavily represented with ensemble members of the GFS and Canadian models while those that maintain stronger high pressure aloft over southern California with weaker onshore flow are more heavily represented with members of the ECMWF.

For Ontario, the spread in the high temperature guidance between the 25th and 75th percentile remains three degrees or less through Monday, then increases to 8 degrees for next Wednesday, 9 degrees on Thursday, and 10 degrees on Friday.

AVIATION

120930Z...Coast/Valleys...Patchy FG is developing over coastal areas, reaching up to coastal mesas in SD County and 10 miles inland into Orange County by 11z. VIS down to 1/4SM in FG. Cigs 100-500 feet MSL with patchy coverage. Any clouds and FG that develop will scatter out 15-17Z in San Diego County, but may linger in Orange County through 18-19Z. Low clouds and FG return to coastal areas around 00z Sat, yielding VIS reductions in same areas as tonight though with an extent a few miles farther inland.

Mountains/Deserts...SKC and VFR conditions expected through early Saturday.

MARINE

Widespread fog over most of the waters tonight. Areas of visibility below 1 NM and locally below 1/4 NM. See the Marine Weather Statement for details. Visibility improvements are anticipated mid morning Friday as fog lifts, becoming low clouds. Low clouds may intermittently scatter out Friday afternoon, then fill in and lower, forming fog and reducing visibility once again below 1 NM for much of the waters by late Friday afternoon, lasting through Saturday morning. Moderate confidence (40-50%) for additional fog Saturday evening. Otherwise, no hazardous marine conditions are expected through Wednesday.

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 Orange County Coastal Areas-San Diego County Coastal Areas.

PZ...None.