Western Drought Will Last Into Fall or Longer

The severe drought that has gripped much of the western half of the United States in spring and summer is likely to continue at least into late fall, government forecasters said Thursday.

The outlook for September through November, prepared by meteorologists with the National Oceanic and Atmospheric Administration, suggests that above-average temperatures are likely across almost all of the West, except for Washington and parts of Idaho, Montana and North Dakota.

Precipitation is expected to be below normal from the Southwest into the Rockies and the Northern Plains.

Together that spells bad news for a part of the country that is already experiencing major effects of drought, including dwindling water supplies, stunted crops, barren grazing lands and exploding wildfires.

“For a lot of the western U.S., we are expecting drought to persist,” said Matthew Rosencrans, a NOAA meteorologist, during a teleconference with reporters.

According to the United States Drought Monitor, currently 47 percent of the land area of the contiguous 48 states is experiencing various degrees of drought, nearly all of it in the High Plains or from the Rocky Mountains westward. Drought affects the entirety of nine states, including California, Nevada, Arizona, Utah, Oregon and North and South Dakota.

In the past month, the drought has become less severe in Arizona and New Mexico. So-called monsoon rains have helped, Mr. Rosencrans said. These occur in summer when atmospheric conditions draw Pacific moisture into the region.

But elsewhere in the West, the dry and hot conditions have continued through July, NOAA announced. California, Nevada, Oregon and Washington experienced their hottest July in 127 years of record keeping, while five other states, including Utah and Colorado, came close to setting records.

The drought situation is particularly dire in California, where 49 percent of the state is in the most severe drought category. Farmers in the state’s Central Valley have had sharp cuts in their water allotments, wells are going dry in some towns and several large wildfires are currently raging, including the Dixie Fire, now the largest single fire in California history.

About half of Utah, one-third of Nevada and one-quarter of Oregon are in the most severe category as well.

Over the next three months, the drought may develop in northeastern Colorado and western Nebraska, Mr. Rosencrans said. The only improvement may be in western parts of Oregon and Washington.

As for the outlook beyond November, Mr. Rosencrans said there was a better than 50 percent chance of La Niña developing in the fall and continuing through the winter.

In La Niña, sea surface temperatures in the equatorial Pacific Ocean drop below normal, triggering changes in atmospheric circulation that can affect weather around the world. In the United States that often, but not always, means warmer and drier conditions across Southern California, the Southwest and Southeast, and colder and wetter conditions across much of the northern part of the country.

Overall, NOAA said, the 48 contiguous states experienced its 13th-warmest July ever. Offsetting the Western heat, below-average temperatures were recorded in the central Plains, parts of the Midwest and Southeast, and northern New England.