textproduct: San Diego

SYNOPSIS

Above average temperatures and weak offshore flow will continue through Wednesday. Patchy low clouds and dense fog along the immediate coast this afternoon will continue into Wednesday morning. A cooling trend begins Wednesday and continues through Friday as a low pressure system moves in from the Pacific, helping build the marine layer and extend low clouds and fog inland. This low will also bring chances of precipitation for locations mainly over and west of the mountains Thursday through Saturday morning. Dry conditions are expected to return Sunday with a warming trend and prevailing offshore flow.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

Visible satellite at 1 PM was showing patches of fog impacting some beach locations. Areas of low clouds and fog are expected to become more widespread tonight into Wednesday morning, with patches of dense fog expected for coastal areas. Areas of fog are expected to limit visibility which may result in minor impacts to travel. For Wednesday night into Thursday, onshore flow is expected to increase ahead of an upper level low which is expected to spread low clouds further inland and lessen the chances for coastal dense fog.

Highs through Wednesday are expected to remain above average as a ridge of high pressure lingers over the US West Coast. By Thursday, an approaching upper level low will become the main influence on our weather. In addition to spreading low clouds and fog further inland, temperatures will drop 5 to 8 degrees for inland locations between Wednesday and Thursday. Cooling will continue into Friday. There remains some uncertainty on when the low will be far enough east for the ridge to re-build over the West Coast, with 50% keeping Southern California under the influence of the trough into Saturday. Current forecast for Saturday through next Tuesday follows the NBM which follows a warmer solution with a few degrees of warming expected Saturday with continued warming into next week. For early next week, all ensemble solutions have a ridge solidly in place over the US West Coast, although there is some lingering uncertainty in the strength of the ridge. There is high confidence in another period of warmer conditions, with less confidence in just how warm it will get.

The aforementioned upper level low will also bring slight chances of showers to the area. Scattered to isolated showers could begin as early as Thursday with slower solutions continuing chances of precipitation into Saturday for some areas. Current forecast has highest chances of rain in and west of the mountains Thursday and Friday, with lingering chances of precipitation into Saturday morning for San Diego County and coastal slopes of the mountains. Latest high resolution guidance is indicating hourly rainfall rates will range from 0.05-0.25" per hour. Rates at or near 0.25" per hour will be fairly isolated and most likely occur Friday. Chances of rainfall totals exceeding 0.50" from Thursday through Saturday, are 10-15 percent for the coast and valleys and 20-30 percent in the mountains. Snow levels will fall to 6500 to 7000 ft by Friday morning. 1-3 inches of snow are expected with totals at the upper end of the range expected above 7000 ft.

AVIATION

201030Z...Coast...Patchy low clouds and FG over coastal waters could briefly touch the coast through 16Z. 20% chance of impacting coastal airports with bases 400 feet MSL and vis 0-2SM. Higher confidence for better coverage of low clouds after 02Z tonight into Wednesday. Bases would be around 400-700 feet MSL and vis 5SM or above.

Valleys/Mountains/Deserts...North and east winds remain elevated for pockets of foothills downstream of mountain passes with gusts 25-35 kts early this morning before relaxing 15-18Z.

MARINE

Patchy dense fog currently out over the waters this afternoon will continue into tonight, likely increasing in coverage some overnight. Visibility reduced to 1 nautical mile or less at times, mainly over outer coastal waters. The fog will eventually lift and clear out by mid-late Wednesday morning.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...None.