It’s raining; so how do those reservoirs look?

It’s raining again, and if you believe weather forecasters and the computer models on which they rely, we’re in for wet weather for most of this week.

That comes on top of an outlandish volume of water that fell across the statelast week, variously computed as between 17 million and 100 million gallons per square mile to 10 trillion gallons statewide.

That’s great news in our parched state, for sure. By now you know, though, that there always has to be a “but,” or in this case, several.

That’s great news, but remember how it quit raining after a beautiful wet December two years ago?

That’s great news, but the Sierra snowpack is still unseasonably thin.

That’s great news, but the state’s reservoirs are still way below normal.

And the biggest “but” of all: That’s great news, but when will we know for sure the drought’s over?

That final question is tough to answer, and the truth is that unless something surprising (though not unprecedented) happens, we’ll only be able to say whether the drought is really over months and months from now. So I’m going to exercise my privilege as executive blogger and stick to what we can say objectively now, based on the mountain of daily statistics from the state Department of Water Resources.

As to the snow, the DWR California Data Exchange Center publishes a daily summary of water content for the Sierra Nevada snowpack. It’s an important number because the state relies heavily on runoff from the Sierra snows to help fill reservoirs. (How much water is stored in the snowpack? About 15 million acre-feet in an “average” year, according to past DWR calculations. An acre-foot is about 326,000 gallons, and one rule of thumb says that’s about enough to supply two average California households for a year.)

So the snowpack so far this year? As of Monday, it’s 41 percent of normal for the date. That’s not great. If you’re looking for a silver lining to that meager-sounding number, here it is: We’re still early in the season, and historically most of the snowpack is built during January and February. So there’s still lots of time to catch up.

You can say the same about reservoir levels. Right now, storage at the big artificial lakes the state uses to manage its water supply is running far behind normal. A daily state report on conditions at major reservoirs says they’re at about 55 percent of the average for mid-December. <more>

Dec. 15, 2014 KQED