Warm and dry weather will continue across the region through the upcoming weekend. Night and morning low clouds and fog will persist on Friday, with less fog for lower elevations near the coast by the weekend into early next week. A low pressure system will bring light showers beginning Tuesday, evolving into heavier rainfall across all areas by Wednesday. The active weather pattern looks to continue with elevated rain chances continuing into the end of next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, Previous Discussion (1057 AM Thursday),
High temperatures for today will be much warmer for the coast and and valleys than yesterday, with highs 10 to as much as 25 degrees above normal. High temperatures for today will range from around 70 near the coast to the upper 70s to mid 80s for the valleys and for the lower deserts. High temperature records for today are most likely to be tied or broken in the mountains, inland valleys, and lower deserts. Some locations that may break records include Campo, Alpine, Big Bear and Idyllwild.
The area of high pressure will begin to break down and flatten over Mexico as a trough pushes southward from the Gulf of Alaska into the Pacific Northwest by early next week. This will lead to greater onshore flow and a subtle cooling trend by the weekend into Monday, though temperatures will still be around 5 to 15 degrees above normal. This will also help the marine layer deepen, leading to foggy conditions to remain in more elevated terrain away from the coast each morning.
A moisture plume/atmospheric river ("Pineapple Express") currently from Hawaii continues to pump moisture into the Pacific Northwest. This system, along with the aforementioned trough to the north, will combine and push this atmospheric river southward into our region by Tuesday through the Christmas holiday. Timing still remains fairly uncertain on when this may occur as the trough of low pressure may elongate over the ocean, delaying the rain's onset. The most likely scenario is to see some light showers developing out ahead of the storm system sometime on Tuesday. Models suggest Wednesday as the period of the heaviest rain as the atmospheric river moves through the area from north to south, with additional lighter showers expected on Christmas Day. Rainfall amounts are still uncertain but areas of the mountains have a 70%+ of seeing 2 inches of rainfall or more during this period. These chances range from 25-45% across the Inland Empire and western San Diego County, to near 65% chance in Orange County. The deserts also look to receive rain from this with a 25-35% chance of 1 inch or more in the lower deserts, slightly higher chances in the high desert. This will lead to an increased debris flow and flooding risk across all areas. Confidence continues to increase that snow levels will be high, mainly above 8,000 feet for the first part of the storm system through Tuesday through early Thursday. Please plan accordingly if you will be traveling for the Christmas holiday as travel impacts are likely.
Ensemble models continue to show an active weather pattern continuing into later next week. The low pressure system that will bring the rain around Christmas may stick around further into next week, bringing additional periods of rainfall and high elevation snow. A lot of this will depend on the exact track of the low pressure system and how cold it becomes. If the low moves slower and remains off the coast, additional periods of heavy precip may occur into next weekend. If the low moves faster, we may see a period of drier weather the days following the Christmas holiday.
182000z, Coast, Patchy low clouds and fog lingering at the coast this afternoon but impacts at coastal TAF sites are unlikely. Low clouds and fog redeveloping along the coast after 01Z Fri, not extending more than 5 miles inland by Fri morning. There will be about a 50-60 percent chance for CIG and VIS impacts at coastal TAF sites between 06Z and 17Z Fri, with cloud bases 002-005 ft MSL and VIS 1-5SM. Periods of VIS blo 1SM possible 10Z-16Z Fri.
Otherwise, SCT-BKN high clouds with unrestricted VIS through tonight.
Patchy fog could reduce visibility to 1 SM late tonight into Friday morning. Otherwise, no hazardous marine conditions are expected through Tuesday.
Ca, None. PZ, None.
