See Drastic Changes To Mississippi, Ohio Rivers In Just 3 Months

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La Niña is expected to last through the winter, and that is not good news for the nation's widespread drought, particularly in the South.

A​ severe drought that already covered much of the West and High Plains last spring has only spread in summer and fall.

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F​ueled by the nation's hottest July through September since 1895 and one of the driest starts to fall on record from Texas to the Mississippi Valley and Northern Plains, a whopping 82% of the contiguous U.S. is classified as either abnormally dry or in drought, according to the Oct. 18 Drought Monitor analysis.

T​hat's the largest such area in the 22-year history of the Drought Monitor.

That has taken a toll on rivers and lakes.

S​tretches of the Mississippi River from the Bootheel of Missouri to northern Mississippi resemble a creek after it plunged to record low levels,​ with major impacts to barge traffic.

P​arts of the Platte River in central Nebraska were almost dry in mid-October.

Following two straight dry winters, reservoir levels in California were well below average. Over 1,200 wells have run dry this year in the state, and some towns are concerned about running out of water.

W​hat much of the nation needs is a wet fall, winter and spring.

Stubborn L​a Niña Not Good News For Many

U​nfortunately, La Niña will likely play a role again at least through winter.

L​a Niña is the periodic cooling of Pacific Ocean water near the equator, generally east of the International Date Line. You may be more familiar with La Niña's counterpart – El Niño, which is a warming of that same ocean water.

I​t usually oscillates every three to four years from warmer (El Niño) to cooler (La Niña) periods, with some periods simply near average, or neutral.

H​owever, it looks likely that La Niña will last into a third straight winter, the first time such a "triple-dip" La Niña will have happened in 22 years.

T​his matters because while not every La Niña is the same, and although it's only one driver of the atmospheric pattern, it usually has an influence on precipitation from fall through early spring in the U.S.

As the composite map from 24 previous La Niñas since 1950 shows, the Pacific Northwest is typically wet in fall and winter during La Niña, while areas to the south, from Southern California to the Southeast coast, tend to be dry.

If this general pattern holds through spring, that's a big concern for the southern drought areas, including California and Texas.

Another dry rainy season would send California into a more critical water deficit next year. The same would be true in the Desert Southwest if another snow-lacking winter occurs in the Colorado River Basin.

I​t also means drought could spread throughout a larger part of the Southeast.

T​hat's exactly what NOAA's winter drought outlook suggested when it was released Thursday. They expect much of the drought area to persist or worsen through February, and drought to spread through much of the Southeast.

T​here is some good news, however: After an exceptionally dry start to fall, drought conditions in the Northwest and northern Rockies are expected to improve or end, given La Niña's tendency for wet winters there.

(​MORE: How La Niña Could Impact A Season's Snow)

S​ome La Niñas also tend to be wet in parts of the Midwest and Ohio Valley, which could improve or end the drought in those areas.

W​hile attention often gravitates to how cold winter will be, how dry it will be is at least equally important for much of the thirsty Lower 48.

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