STORMY FOR LAST WEEK OF FEBRUARY INTO MARCH

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There is excellent model agreement on an upcoming stormy period kicking off across Northern California in less than a week. For now a cutoff low pressure center is churning off the coast and headed south, but will miss us by a few hundred miles.

After this system passes south, high pressure will build in briefly for the President’s Day weekend.

It will stay cool, with mostly sunny skies over the long weekend. That all changes by the 22nd or 23rd, as deep, amplified low pressure pushes into the West from the north and east. Both of the major models as well as their ensemble members are in agreement on this, giving us lots of confidence in the upcoming major pattern change.

The low will push far enough west so that storms can spin up off the coast, instead of just dropping down over land. That means more rain for us. The first storm may be long lasting, with a low spinning off the coast sending in showers from Wednesday the 22nd all the way into Sunday the 26th.

No atmospheric rivers, but cool rains and accumulating mountain snows for Northern California that will begin to add up. The GFS model has other storms dropping in on the 27th and the 2nd of March.

We should address some models that show accummulating snow across portions of the Bay Area, North Bay and low elevations of NorCal late next week. These are very likely overdone, as this setup is extremely rare and the air mass must have very little or no over ocean transport in order to bring widespread snow to low elevations in our region. Still, the Northern Sacramento Valley and our North Bay mountains may see accummulating snow down to about 1K feet, and there could be flurries even lower. Here is the European snowfall outlook for late next week, which I’m sure will change. Other models are not as bullish on snow.

It’s pretty early to talk about rainfall totals, but the overall pattern change looks all but certain. Here is the European ensemble outlook for rainfall into early March.

All of the models show us receiving more than average rain and snowfall between February 22nd and March 3rd.

After early March? The long range models are mixed on whether the rest of the month brings significant rains. For now, most of the state continues to be above average in precipitation for the date.

Here in the North Bay, we’re generally at 100-150% of average rainfall for the date. The coming rains will help us stay above average.

Finally, the North Bay’s largest, most important reservoir, Lake Sonoma currently holds 243K acre feet, just short of its maximum water supply pool of 245K acre feet (99% of capacity), and above the average for the date of 216K acre feet (88% of capacity).