A low pressure system off the coast will move over the region through Thursday, bringing cloudy skies and areas of showers. The heaviest rain will fall late Wednesday night through Thursday morning. A period of drier weather will occur for a short time on Friday. A series of weak weather systems will bring another increased chance for light showers to occur over the region by this weekend, potentially into early next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, NEW AVIATION DISCUSSION FOR 12Z TAFS,
Satellite imagery this morning shows a dynamic area of low pressure off to our west pulling in clouds and subtropical moisture from the south. Kind of like yesterday afternoon, radar shows very elevated showers, where some folks may be able to see a sprinkle or two. Hi-res model guidance shows high-level moisture and showers beginning to overspread the area by late morning into the afternoon today. Heaviest showers will be along the coastal slopes with lower elevations receiving light amounts. A frontal boundary with the storm system will approach the area late this evening through Thursday morning, where the heaviest rain will be expected. As this occurs, southerly winds will strengthen this evening and overnight as well, mainly at the coast. If planning any New Year's celebrations tonight, be prepared for rain showers across our entire forecast area, as well as some breezy winds near the immediate coast near 20 mph at times. This subtropical moisture ridden pattern will continue the more humid and warmer evening temperatures over the next few nights as well.
The frontal band will lift over region on Thursday morning. This will be associated with slight increased instability as the vort max passes over SoCal, so a slight chance of thunderstorms have been added to the forecast for much of Thursday morning and afternoon for areas west of the mountains. Any thunderstorm will be capable of producing heavier rainfall, gusty winds and small hail. In terms of rainfall, the heaviest is expected along the coastal slopes of the San Bern Co Mountains with 3-5" in total by Thursday night. Chances for 1"+ or more of rainfall is near 50-60% in Orange County and the western Inland Empire, slightly lower chances in northern SD County. Chances become closer to 15-30% for the eastern parts of the Inland Empire and the San Diego metro. The deserts will also receive rainfall, but most areas will see between 0.25"-0.75". Some hourly rain rates will be elevated areas surrounding the LA Basin, leading to localized flooding on streets and near recent burn areas during this event. Snow levels will remain over 8,000 feet, with most mountain communities receiving only rain.
A brief drying period will occur by Friday as the weather system exits to the east and a weak ridge moves in its place. While most of our region will likely remain cloudy, chances for sunshine and slightly warmer temperatures are in the forecast for the desert regions. Highs in the high desert will near 60 degrees with highs near 70 degrees across the Coachella Valley and Anza Borrego desert areas.
Another Pacific storm system currently in the Gulf of Alaska will move closer to SoCal by this weekend, providing another chance for showers on Saturday morning and continue through the weekend. While exact timing of the rain and rain totals remains uncertain, it is looking increasingly likely that this rain event will be lighter than the one we are about to see in the coming days. Snow levels may be slightly lower by this time period as well. This will continue the near average temperature and mostly cloudy weather pattern that we will be seeing this week. Global ensemble models start to diverge on what becomes of this weekend's weather system and how it evolves by the first half of next week. Periods of showers remain possible for this entire time period as some models suggest a series of weak disturbances rounding the southern portion of the weather system. Though the exact details aren't in view too well for now, a cloudier, cooler and potentially wetter pattern looks to remain as we enter the early part of January.
311030z, Generally VFR conditions through this morning with BKN-OVC high clouds 8000-12000 ft. Gusts up to 20-30kts return after 18z, prevailing through this evening. SCT -SHRA is already beginning to move up from the south, with bases lowering to 5000-7000 ft MSL. Intermittent minor VIS reductions of 4-6SM possible from the coast to the mtns into this afternoon. SHRA increases in coverage and becomes heavier starting 03-06z Thu with bases lowering again to 2000-4000 ft MSL. Widespread MVFR CIGs/VIS likely with intermittent IFR through the Thursday morning.
Southeasterly winds strengthen this afternoon, with conditions hazardous to small craft this evening through Thursday afternoon, bringing south to southeast gusts around 25 knots. Winds turn westerly before diminishing late Thursday afternoon. Then, no hazardous marine weather conditions expected through Saturday.
Ca, Flood Watch from this evening through Thursday evening for Orange County Coastal Areas-Orange County Inland Areas-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-Santa Ana Mountains and Foothills.
PZ, Small Craft Advisory from 7 PM this evening to 3 PM PST Thursday for Coastal Waters from San Mateo Point to the Mexican Border and out to 10 nm-Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.
