News•October 11, 2012

Some Improvement, Some Deterioration for Drought in U.S.

Despite a series of low-pressure systems that brought rain to the northern Great Plains, the Midwest, the Mid-Atlantic states, and Florida over the past week or so, the drought that has gripped the Lower 48 states since the spring (and even longer than that, in some areas) is still holding on, according to the latest update of the U.S. Drought Monitor.

The report shows that while the overall drought footprint has shrunk slightly, the scope of the most intense areas of drought have actually expanded a bit. As of October 9, 63.55 percent of the continental U.S. was reported in moderate drought or worse, compared with 64.58 percent the previous week.

Areas in extreme or exceptional drought, the two highest categories, expanded from 20.12 percent to 20.15 percent of the nation, excluding Alaska and Hawaii, with South Dakota, Wisconsin and Minnesota bearing the brunt of the expansion.

The drought is the worst such event to strike the U.S. since the 1950s and is comparable in some ways to the “Dust Bowl” era droughts of the 1930s. While the drought was most likely triggered by a particular pattern of ocean temperatures in the Pacific and Atlantic Oceans, it was likely aggravated by extreme heat this summer. July was the warmest month of any month on record, and the summer was the third-warmest on record. Climate studies have shown that the odds of severe heat waves are increasing due to manmade climate change.

The hardest-hit states continue to be concentrated in the Great Plains, where most of Nebraska is suffering from exceptional drought, and South Dakota has seen the area under severe drought, or worse, expand from 82.3 percent the previous week to 91.39 percent this week.

In the Ohio Valley, which suffered a great deal earlier in the summer, the drought has receded significantly thanks to higher than usual precipitation over much of the past month. The drought has backed off as well in northern Georgia, parts of Louisiana, and portions of Arkansas and Tennessee, and in the Mid-Atlantic states of Maryland and Virginia.

The drought outlook is based on climate forecasts that reflect the potential effects from a developing weak El Niño event in the Pacific Ocean. Such events tend to produce above average winter precipitation across the nation’s southern tier and Ohio Valley, while leaving the Pacific Northwest drier than average.

In recent weeks, signs of the developing El Niño have become more muted, casting doubt on whether it will actually take shape, and if so, how strong it might be. The fate of the El Niño will have a major impact on the prevailing winter weather pattern across the U.S.