Against that background, the deluge is bringing smiles, but the joy is tempered. Climatologists warn the record rain and snow have missed the Northwest, and the gains could be erased by another hot, dry spring.

Moreover, a deluge of rain — downtown Los Angeles had its wettest 15 consecutive days on record, with 17 inches falling in the period ending Monday — is not the best for drought-busting.

Heavy rain quickly saturates the topsoil. Then the rest runs off rather than soaking into the ground. Gradual rain over long periods, or slowly melting snow, allows water to seep down, doing a far better job of replenishing groundwater.

Most of the Western United States remains in some sort of drought, from Canada to Mexico, from the Sierra Nevada range to east of the Rocky Mountains. The most severe conditions are in Montana, Idaho and Wyoming.

"No optimism here yet," said Ted Day, a water engineer for the U.S. Bureau of Reclamation's Pacific Northwest Region in Boise, Idaho. "What is going on down there in California and Nevada is just missing us."

Runoff from the storms is expected to raise the level of Lake Mead, the main source of water for Las Vegas, by 2 feet. However, over the years the reservoir has fallen 90 feet below full. Boat ramps and marinas were designed for a lake at least 49 feet higher than the current level.

In Arizona, the entire eastern half of which is in a severe drought, the heavy rains have some rivers running for the first time in seven years.

"It makes us feel pleasantly optimistic, but we have a long way to go," said Herb Guenther, director of the Arizona Department of Water Resources.

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Contributing: Daisy Nguyen