United States: Water surplus in N. Plains, TN, Carolinas, Deep South

25 March 2020

THE BIG PICTURE
The 12-month forecast ending November indicates moderate to extreme water surpluses in the Dakotas, particularly widespread in South Dakota, with some areas reaching exceptional intensity. Surpluses will extend well into Nebraska and are also forecast in southern Montana and several areas of Wyoming.

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Some moderate surpluses are expected in a few pockets of southern Minnesota and eastern Wisconsin and will form a path down the center of Michigan’s Lower Peninsula.

Nearly normal water conditions are forecast for much of the northern Ohio River Basin, but surpluses of varying intensity are predicted in the Basin’s southern region, extending further south through Mississippi, Alabama, Georgia, and into the Carolinas. Anomalies are expected to be extreme to exceptional in west-central Georgia, northern Alabama, and central Mississippi. Moderate surpluses are forecast for southern Missouri, northeastern Oklahoma, and pockets of Kansas and Arkansas.

Southern Texas can expect deficits, primarily moderate but more intense in a few pockets including severe anomalies around Houston. Deficits are forecast for southern Florida as well and will be intense south of Lake Okeechobee. Nearly normal conditions are expected in the U.S. Northeast and Mid-Atlantic with some small pockets of deficit including in southern Delaware.

In the West, deficits of varying intensity are forecast for much of California north of Los Angeles. Deficits will be generally severe in the south and moderate in the north, reaching into Nevada. In Nevada’s northeastern corner surpluses are forecast. Intense deficits are expected in southwestern Colorado, some pockets of moderate deficit in Utah and New Mexico, and surpluses in southeastern Arizona.

The Pacific Northwest can expect scattered deficits which will be intense in north-central Oregon and the Columbia River region in central Washington. Some surpluses are also in the forecast east and north of Seattle. Intense deficits are forecast for Idaho’s Salmon River Mountains.

Outside the contiguous U.S., surpluses are forecast for much of Hawaii and mild deficits in Puerto Rico. In Alaska, surpluses are forecast in the Koyukuk and Kobuk River regions in the north, in a wide path from the base of the Alaska Peninsula into the center of the state, and on the southwest coast near Bethel. Some deficits are expected from Anchorage leading east.

FORECAST BREAKDOWN
The 3-month maps (below) show the evolving conditions in more detail.

From March through May, moderate-to-exceptional surpluses will persist in the Dakotas and Nebraska, while moderate surpluses extend westward into Wyoming and Southern Montana, and eastward into Wisconsin. Surpluses likewise persist in the American South extending westward into eastern Kansas and Oklahoma, though these will be more moderate anomalies than were observed this winter (December through February). Small pockets of intense surpluses persist into the spring season for southeastern Arizona and Some parts of northern New Mexico.

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Moderate to severe deficits observed in eastern Texas in December through February will retreat to normal to moderate-deficit condition in March through May, as will deficits in the Florida Peninsula. California will experience statewide deficits of abnormal to extreme severity. Deficits extend northward into Oregon and Washington, though intense winter deficits along the Cascade Range observed in December through February ease in severity over the March-through-May period. Deficits observed in northern Virginia in December through February will retreat to near-normal conditions, transitioning to abnormal surpluses in the south. Normal to moderate-deficit conditions are forecast for southern New England into the Mid-Atlantic, while Upstate New York and parts of Vermont and New Hampshire will experience moderate surpluses.

From June through August, anomalies east of the Mississippi will retreat to near-normal conditions. Surpluses in the Midwest retreat to near-normal conditions east of South Dakota but persist in the Dakotas and northern Nebraska with abnormal to exceptional severity. Surpluses will shrink in Montana and Wyoming, and transition to abnormal-to-moderate deficits in Idaho, Nevada, and Utah. Colorado’s areas of deficit will normalize. Deficit severity will ease in California, the Pacific Northwest, and Idaho.

The forecast for the final months – September through November – indicates widespread surpluses in South Dakota leading into North Dakota and Nebraska, and scattered pockets of surplus in Montana and Wyoming. Generally moderate deficits are forecast in isolated pockets of the Mid-Atlantic States, the panhandles of Texas and Oklahoma, Michigan’s Upper Peninsula, and California and the Southwest.

(It should be noted that forecast skill declines with longer lead times.)

IMPACTS
Winter snowpack in the Sierra Nevada Mountains is less that half the normal, with a snow-water equivalent of 11.5 inches, only 47 percent of average for the end of February. The statewide average at the end of the month was even a bit lower at 46 percent. With no measurable precipitation during February in the Northern Sierra, officials from California’s Department of Water Resources say that the month will go down as the driest February in the history of the department’s record-keeping.

In the Great Lakes region, Lakes Michigan, Superior, Huron, and Erie all set new high water levels for February. Lake Michigan and Lake Huron broke the record by half a foot, equaling 4.8 trillion gallons. And, February 2020’s water level bested 2019’s by 17 inches. With unusually high precipitation in the region, experts predict that Michigan and Huron will continue to break monthly records through August. High water levels in the Great Lakes system have delayed the start of spring shipping on the St. Lawrence Seaway by two weeks, pushing it out to April 1.

In an effort to avert a repeat of last year’s disastrous flooding in the Missouri River system, the Army Corp of Engineers increased water releases from Gavins Point Dam on the South Dakota-Nebraska border to 41,000 cubic feet per second at the end of February, significantly more than the normal release of 17,000 cfs for this time of year.

NOTE ON ADMINISTRATIVE BOUNDARIES
There are numerous regions around the world where country borders are contested. ISciences depicts country boundaries on these maps solely to provide some geographic context. The boundaries are nominal, not legal, descriptions of each entity. The use of these boundaries does not imply any judgement on the legal status of any territory, or any endorsement or acceptance of disputed boundaries on the part of ISciences or our data providers.

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