Above average temperatures and weak offshore flow will continue through Tuesday. Patchy low clouds and dense fog along the immediate coast tonight, with increasing chances of night and morning low clouds and fog into the middle of the week. 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 a 10-20 percent chance of precipitation Thursday and Friday. Starting Sunday, dry conditions are expected to return with a warming trend and prevailing offshore flow.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Evening update, A marine airmass has returned to parts of the coast this evening with surface dew points rising into the mid 50s. Patchy fog is developing over the coastal waters and locally nearing the coast, but weak drainage flow is already evident in the surface obs and will be aided by strengthening offshore flow overnight. Any dense fog along the coast is likely to remain patchy and intermittent overnight. Low clouds and fog are forecast to be more widespread Tuesday night into Wednesday as onshore flow returns, possibly moving into the beaches by Tuesday afternoon (20-40% chance).
Previous discussion, 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 60% keeping Southern California under the influence of the trough into Saturday. Current forecast for Saturday through next Monday follows the NBM which follows a warmer solution with the ridge starting to build over the West Coast earlier. For early next week, all ensemble solutions have a ridge solidly in place over the US West Coast, with high confidence in another period of warm and dry conditions.
The aforementioned upper level low will also bring slight chances of showers to the area. Scattered to isolated rain could begin as early as Thursday with slower solutions continuing chances of precipitation into Saturday. Current forecast has highest chances of rain in and west of the mountains Thursday and Friday. There still remains some uncertainty in rainfall rates and amounts but most of the ensemble guidance is currently indicating light rain with minimal accumulations.
200400z, Coasts, Isolated patches of low clouds/FG over coastal waters currently. Patchy FG expanding in coverage some overnight with a 40-50% chance for impacts along parts of the immediate coastline after 09Z. Local vis reductions less than 1SM if FG develops with cigs 100-400 ft. Any FG clearing from the coastline 14- 16Z Tuesday. Higher confidence for areas of low clouds/FG over coastal areas Tuesday night with cig/vis reductions starting around 03-06Z Wed.
Valleys/Mountains/Deserts, North and east winds remain elevated for pockets of foothills downstream of mountain passes with gusts 20-30 kts. Winds relax 15-18z Tuesday.
Patchy dense fog tonight into Tuesday (50-60% chance), reducing visibility locally below 1 nautical mile. Otherwise, no hazardous marine conditions are expected through Friday.
Ca, None. PZ, None.
