Warm and dry weather will continue through Tuesday, with high temperatures 5 to 15 degrees above normal. Marine layer low clouds and fog could return to the coastal areas as early as tonight into Tuesday morning but confidence is low. Offshore flow briefly returns tonight into Tuesday morning with breezy conditions below the passes, weakening Tuesday night. Chances for Coastal low clouds and fog improve each night and morning for Tuesday night through the end 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 even further and extend the low clouds and fog inland. This low will bring a 10-15% chance of precipitation for Friday into Saturday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This morning, skies are clear except for a few high clouds. There is no marine layer presence in spite of the offshore flow continuing to weaken. Dry conditions at the surface extend from inland all the way to the coast in many areas. Relative humidity is high at a few coastal locations so the chances for patchy low clouds/fog can't be eliminated. High-resolution models show chances for marine layer clouds/fog returning to the coastal areas as early as tonight but probabilities are low.
Offshore flow strengthens again late tonight into Tuesday, effectively preventing a marine layer return until Tuesday night/Wednesday morning. Offshore flow weakens again late Tuesday but chances remain low for a marine layer return until Wednesday night when onshore flow allows the dry air at the surface to be displaced farther inland.
A high pressure ridge persists over SoCal through Wednesday, weakening over time as a low pressure system approaches from the west. Daytime high temperatures remain 5-15 degrees above normal through Tuesday for the coastal areas and inland valleys. Temperatures are a little lower on Wednesday as onshore flow begins to spread the marine air inland.
Temperatures lower more significantly for Thursday through Saturday as a low pressure system from the Pacific displaces the high pressure ridge and brings cooler, more moist air to the entire region along with widespread clouds. This system will also bring small chances for light precipitation Friday into Saturday, mostly for the mountains westward to the coast. Currently, chances for measurable precipitation in any 6-hour period remain below 25%. A significant number (about 30 percent) of ensemble members show measurable precipitation for Friday and Saturday.
By early Sunday, the low has moved east and weakened while high pressure begins to rebuild over the West Coast. This will bring a return of fair weather with temperatures again on the rise. By next Monday, high temperatures are once again as much as 8 degrees above normal for areas west of the mountains.
191800z, 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 to increase after 20z this afternoon for pockets of foothills downstream of mountain passes with gusts 20-30 kts.
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.
