Drought has engulfed nearly a third of the United States, threatening to confront some places this summer with what experts say could be their worst water shortages in years.

“This is a sleeping giant,” says climatologist Mark Svoboda, at the National Drought Mitigation Center in Lincoln, Neb. “The impact is still to come.”

Already, New York and Baltimore are pumping water from temporary supplies normally avoided for their potentially less desirable color or taste. Thousands of shallow wells in New Hampshire and Georgia have run dry. In Kansas, some ranchers are hauling in water or selling off cattle.

Yet a much stiffer test will come this summer when farmers water crops, homeowners douse lawns and gardens, and high temperatures evaporate more water faster. Without a rainy spring, some places in the East may face a summer of water problems that rival record droughts of the 1960s, according to Harry Lins, a drought specialist at the U.S. Geological Survey.

In typically dry Southern California, the recent feeble wet season is apt to harden into full-blown drought, say government and private forecasters. Bernie Rayno, a forecaster at the private AccuWeather service in State College, Pa., is more worried about that region than the East.

“They’re missing their window of opportunity,” he says. “Once you get past that, you’re not going to get rain there.”

In the last six months, Los Angeles has seen just over a third of its usual 11 inches.

Overall, drought has spread to about 30 percent of the country, according to forecaster Richard Tinker at the Climate Prediction Center of the National Weather Service. That is an unusually broad reach but still far short of the 1930s Dust Bowl. In those years, up to 70 percent of the country was parched, and dust clouds sometimes blotted out the sun for days at a time.

Drought conditions now run in two vast Eastern and Western strips, each hundreds of miles across, from Maine to Georgia and Montana to Texas, according to a federal-academic partnership that puts together the U.S. Drought Monitor map.

Forecasters say it’s especially difficult to make long-range forecasts for the Northeast.

But they are hopeful that the rains typical of spring will relieve some of that region’s drought conditions, which took hold only last fall. Drought has lingered elsewhere, like Texas and Georgia, for up to six years.

There is no single accepted definition of drought. But one popular standard defines it as 70 percent of normal rain or snow for three straight months.

Several factors have combined to parch so much territory, drought experts say. La Nina, a cooling of Pacific Ocean surface waters, is blamed for recent warm, dry winters in the Southeast and warm, dry summers in the northern Rocky Mountain states.

A northern track taken by high-altitude winds of the jet stream has steered this winter’s storms toward the Pacific Northwest and Midwest. Persistent high pressure in the East has also locked out storms.

Finally, one of the warmest winters on record in some places on the East Coast is letting water soak into soft ground, instead of running off to replenish surface supplies.

Communities along the coast have issued drought watches and warnings. Many have already appealed for voluntary cuts in water use. Some governments have taken their own steps. Connecticut environmental officials said Wednesday they were suspending the annual opening of dams for the first time since 1981. The water release is meant to scour riverbeds to improve fish habitats.