10 DAYS OF (MOSTLY) SUNNY AND DRY FOR NORTH BAY. THEN, STORMS RETURN?

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After a quick moving storm late Wednesday, the North Bay can expect mostly sunny and dry weather through the next 10 days. After that there are signs that the weather pattern may open up to more storms reaching California from the north.

SHORT TERM

The satellite view Wednesday shows the next, and final storm moving south into Northern California. This storm will bring a quick shot of a quarter to half inch of rain across the North Bay late Wednesday into early Thursday AM.

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After that, high pressure quickly builds in, bringing sunny skies for at least a week.

Because we will be seeing cool continental air flowing down from the north (and not from the west off the Pacific), temperatures will remain cooler than normal for the next week. That means highs mostly in the cool upper 50s, and lows in the 30s.

Still, as we get to the last few days of January, the ensemble forecast models suggest the pattern begins to change once again, with high pressure retrograding (backing up) to the northwest to near the Aleutian Islands and a trough of low pressure becoming established across the West.

Why is this happening? Two major factors seem to be the Madden Julian Oscillation (MJO) moving into favorable zones (Indian Ocean), and the Pacific North American Oscillation (PNA) going negative, which is typical of La Nina, and opens the door to cold low pressure dropping south along the Pacific Coast.

What happens then? In theory this opens the door for (cold) storms to begin to drop down from the north into California, over land or just off the coast. And that’s what the ensemble forecast models are already showing, going from dry in the last days of January, to wet by the first days of February.

Already the GFS deterministic model is showing storms reaching California in the last days of January, and the first week of February.

The same GFS model is showing a good amount of rain reaching Northern California by the 3rd day of February. The other models show it too, but for now the GFS is the wettest.

So, we have a dry spell, with time to dry out a bit, but the good news is that the rain may well return after about 10 days.

Finally, let’s take a look at the current water supply at our largest reservoir, Lake Sonoma. Runoff continues, and the reservoir is now at 231K acre feet, significantly higher than average for this time of year. It is also just 14K acre feet below it’s full water supply pool of 245K acre feet. That represents an increase of around 120K acre feet since the parade of storms began just after Christmas!

And, once again, don’t be confused by the capacity percentage in red. That represents a state calculation of the full flood control capacity of Warm Springs Dam (Lake Sonoma), which is 381K cubic feet. But that’s not the figure used to determine the water supply capacity.