Over the past week, storm after storm has pummeled central and northern California, denting if not erasing a multiyear drought.

The federal government’s U.S. Drought Monitor published Thursday morning declared that the northern third of the state is now entirely drought-free. Reservoirs are filled and streams are flush with water — at or near record flows.

“With more than a foot of precipitation falling on the Sierra Nevada (locally 20.7 inches at Strawberry Valley, CA), most major reservoirs were at or above its Jan. 10 historical average,” the Drought Monitor reported.

The amount of rain and snow so far this year is unsurpassed in historical records in the Northern Sierra, San Joaquin and Tulare basins. The Northern Sierra tallied 26 percent of its annual precipitation in the first 10 days of January alone.

The percentage of California which has emerged from drought leapt from 19 percent to 35 percent in the past week. Just three months ago, the entirety of California had some sort of drought designation.

In some areas, the problem is too much water rather than too little.

Heavy rain and snow is expected to ease on the West Coast after severe flooding forced thousands to evacuate. (Reuters)

On Tuesday, for the first time in more than a decade, California officials opened the floodgates at the Sacramento Weir to divert excess water into fields to prevent flooding in parts of the city.

Snow amounts at high elevations have been profuse, up to 12 feet in just the past week. The snow piled up so high some ski resorts were forced to close:

The Drought Monitor said the amount of water contained in the state’s snowpack, as of Monday, was 135 percent of normal and rising.

The excessive amounts of rain and snow have resulted from a configuration of weather systems that have pointed “atmospheric rivers” at the Golden State. These rivers are narrow but intense streams of moisture sourced from the tropics. Some call the moisture feed the “Pineapple Express” given its origins near Hawaii.

A typical atmospheric river transports a quantity of water — in the form of vapor — equivalent to 26 Mississippi Rivers. As much as half of the rain and snow that falls in West Coast states comes from these rivers.

Relatively light amounts of precipitation are predicted in California for the next day or two before a dry weekend, but the weather pattern next week may promote another onslaught of heavy rain and snow. NOAA’s Global Forecast System (GFS) Model, while subject to change, predicts an intense atmospheric river will again bombard the northern half of California in about five to seven days.

As many reservoirs and streams are full, the added precipitation threatens a new round of flooding problems next week.

Although storms have hammered Northern California, with more expected, they have only brushed Southern California, where drought improvements have been much more modest. Severe (or worse) drought lingers in many areas of the southern half of the state, where the drought is in its fifth year.