Above average temperatures and weak offshore flow will continue through mid-week. Patchy low clouds and dense fog may develop 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 for the end of the week. 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,
Mostly clear skies have been observed this afternoon, with a few high clouds moving north to south across the area. Weaker offshore flow is expected tonight resulting in a slightly higher chance of patchy low clouds and dense fog developing along the immediate coast into Tuesday morning. If dense fog does make it to land, minor travel impacts may occur due to the limited visibility. Chances of low clouds and areas of dense fog developing increase for Tuesday into Wednesday morning. For Wednesday night into Thursday, onshore flow is expected to increase ahead of an upper level low which would increase the inland extent of low clouds and lessen the chances for coastal dense fog developing.
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.
192200z, Coasts, Mostly clear skies today and this evening. Patchy low clouds/fog look to develop over the waters around 06-09z Tuesday morning. There is ~50-60% chance of dense fog reaching the coasts between 09-16z. Should these clouds sneak ashore, very low CIGs 0- 400ft MSL expected with VIS 0-3 SM. Any low clouds/fog will clear back out by 15-17z Tuesday morning.
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 (50-70% chance), reducing visibility locally below 1 nautical mile. Otherwise, no hazardous marine conditions are expected through Friday.
Ca, None. PZ, None.
