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Weather this week starts quiet but gets increasingly active

Rainfall returns
Posted at 4:41 PM, Dec 20, 2021
and last updated 2021-12-20 20:50:40-05

The week is beginning with plenty of high cloud cover, although Tuesday will likely see a little more sunshine than Monday.

Despite the slow start to weather this week, an increasingly active pattern is likely. The tough part about the forecast is the uncertainty in terms of the intensity of the upcoming storms. Models essentially agree that rain Wednesday and Thursday is likely and also likely decent rain, what models disagree about is the high side potential.

Some models like a solid dousing while others predict a more garden-variety storm. I'm splitting the difference. I think 1-3" near the coast with .5-1" inland (up to 3" in the hills of the Santa Ynez range and the SLO County north coast).

Rain will be light on Wednesday but continue into Thursday where more substantial rain is likely.

The wettest spots appear to be the Santa Ynez mountains where 1.5-3 inches of rain is possible.

The other hot spot will be the NW corner of SLO county where similar amounts could fall.

Most coastal and valley locations will range from 0.5-1.5 inches through Thursday night.

Rain rates are very likely to remain under 0.50" per hour with a small risk of exceeding this rate in western SLO County.

West winds will become moderate to briefly strong at times on Thursday for the foothills and mountains with gusts of 40-60 mph.

Snow levels will remain above 8k feet, but start to fall toward 5500 feet Thu night.

Travel at high elevations like the Grapevine will need to be monitored carefully.

Currently, I highly encourage people to stay up to date for forecast refinements as the system nears.

There is a broad subtropical feed is streaming toward Baja and Southern CA today. This moisture plume originates well south of Hawaii and the axis of this plume will be overhead with the first storm this week, then drift to our south on Friday before making another surge northward on Saturday. This part of the Pacific is difficult for models to pinpoint details and subtle movement of this moist plume makes a big difference in our rainfall totals.

In the short term, we could see more early clouds in the southern Salinas River Valley as we saw this morning but the currently high cloud deck also makes that a more challenging forecast.

There is some weak offshore flow for Tuesday so shooting for low 60s highs.

Beyond Tuesday I'm going with upper 50s and low 60s for all the extended forecast.

The bulk of the rain is done Thursday but scattered rain showers are possible Friday.

Saturday-Monday more showers are possible but not as significant likely as the Thursday rainfall.