Rain looks to begin Wednesday but the main storm impact Thursday

Pismo Beach fire sunset
Posted at 4:29 PM, Dec 21, 2021
and last updated 2021-12-21 20:54:22-05

The Central Coast has seen a spray of high clouds to start the week, this is getting pumped in by a strong jet over the Pacific. This moisture supply is key to the system which lurks off the coast. This slow mover will finally start to make an impact on Wednesday. I think the day starts dry but showers could begin in the later morning with rain becoming more likely by hour into Thursday.

This system has a lot going for it, a strong upper-level low, a strong jet, south winds during the system, and a large upper-level trough. If this all lines up, I think the north coast of SLO county could see 2-5+" of rain with 1-3" for coastal valleys of SLO county. .5-2.5" of rain for coastal Santa Barbara County and the deep interior of both counties could see a wide range from light to up to 2". Rainfall looks to start wrapping up Thursday evening and is likely done by Friday morning.

The origin of the moisture will be from the sub-tropics so snow levels will be very high through Thursday night, generally above 8000 feet, then quickly lower to 4000 to 5000 feet on Friday as the front moves east and a cooler airmass filters in. Once the colder air moves in on Friday, there could be several inches of snow down to 5000 feet or so with some hazardous wintry driving conditions developing for travel outside the Central Coast.

Friday looks quiet. Models agree the active pattern continues but disagree on the specifics regarding a series of smaller storms after Friday. I think the EURO has the best handle on it with a Saturday lighter system, a break Sunday, and another lighter system Monday. If we are saturated or have any difficulties with infrastructure from Thursday these small systems could have an impact but by themselves, they are likely just additional shots of lighter to moderate rainfall. It is worth paying attention to for travel-sake.

I think .25-.75" of rain for the extended forecast looks good with perhaps .5-1.5" in some of the hills. Saturday thru Tuesday look cold so snow levels will likely drop a lot. 3000 and 5000 foot snow levels Saturday thru Tuesday. The hills around the Cuyama Valley could even see some snow.