United States: Intense water surplus to persist in the Dakotas

20 November 2019

THE BIG PICTURE
The 12-month forecast ending July 2020 indicates water surpluses of varying intensity in the Northern Plains States, Upper Midwest, and Michigan. Surpluses will be exceptional in pockets of the Dakotas. Primarily moderate surpluses are expected along the Upper Mississippi River from St. Louis. Pockets of surplus are also forecast for Montana and Wyoming with moderate surpluses along the Yellowstone River.

ISciences_United_States_Composite_Adjusted_201908-202007_12mo_panel.png

Deficits are forecast in Texas, the Southwest, and California. Moderate to severe deficits are expected in California; deficits will reach extreme to exceptional intensity in Nevada, Utah, Colorado, Arizona, and New Mexico. In central West Texas, deficits will be moderate to exceptional, and moderate deficits are forecast along the Canadian River in the Panhandle.

In the eastern U.S., deficits are forecast in West Virginia, pockets in surrounding states, and Delaware. Deficits are also expected in pockets throughout the Southeast, including the Carolinas, Georgia, Alabama, and Florida. Deficits could be intense in West Virginia and south of Lake Okeechobee in Florida. In the Northeast, moderate surpluses are forecast for eastern Maine and moderate deficits in southern Vermont.

Outside the contiguous U.S., surpluses are forecast for much of Hawaii and moderate deficits in western Puerto Rico. In Alaska, exceptional deficits are forecast along the southern shore of the state from the Alaska Peninsula through Kodiak, Anchorage, and Valdez. Deficits are forecast in the middle reaches of the Tanana River. Surpluses are forecast in the Koyukuk River Watershed in northern Alaska.

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

From November 2019 through January 2020, widespread surpluses of varying intensity will persist in the Plains States and the Upper Midwest. Surpluses will stretch from North Dakota through northern Oklahoma with widespread extreme to exceptional severity in the Dakotas. Extreme surpluses are expected in Minnesota and central Nebraska, and severe surpluses in Wisconsin’s southern half, Illinois’ northern half, and spanning the center of Michigan’s Lower Peninsula. Surpluses of varying intensity are forecast for southern Montana, Wyoming, southern Idaho, northwestern Utah, northern Nevada, and pockets of Oregon.

ISciences_United_States_Composite_Adjusted_201908-202007_3mo_panel.png

Deficits will downgrade overall in the Southwest, but intense anomalies are forecast for southwestern Colorado and into north-central New Mexico. Exceptional deficits are forecast in Idaho’s Salmon River Watershed. Along the Eastern Seaboard, deficits will diminish considerably from the Virginias through the Southeast, with near-normal conditions forecast in most regions. Deficits are forecast, however, from West Virginia’s eastern tip through Delaware, becoming exceptional in southern Delaware. Intense deficits will persist in southern Florida, increasing somewhat. In the U.S. Northeast, moderate surpluses are expected in northern New York State and southern Maine.

From February through April 2020, deficits will nearly disappear nationwide while surpluses in the north-central U.S. continue. Some intense deficits will persist in central Colorado and severe deficits in Florida south of Lake Okeechobee. Surpluses will persist with intensity in the Dakotas, downgrading slightly, and will trail down through Nebraska and western Kansas. Surpluses will moderate and shrink from Minnesota through Michigan but will increase in Wyoming and Montana, emerging along the Missouri River in Montana. Some pockets of moderate surplus are forecast for Idaho, Nevada, Oregon, and the central region of the Sierra Nevada Range in California. In the U.S. Northeast, surpluses will nearly disappear.

The forecast for the final months – May through July 2020 – indicates normal conditions east of the Mississippi and in the Southern Plains States, surpluses in the Dakotas and moderate deficits the Southwest and Northwest.

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

IMPACTS
It’s been a wet fall in North Dakota, with most river levels in the 90th percentile, according to one state meteorologist. And though the Red River is slowly receding after hitting record levels, there is much concern over spring flood outlooks with so much water available to be locked into the system by freezing temperatures. Snowfall accumulation in the northeastern region of the state was between 3 and 4 feet from the beginning of October through much of November, according to NOAA.

A federal disaster declaration has been approved for South Dakota regions affected by storms and flooding in September. This is the fourth disaster declaration the state has received this year for separate flooding events in March/April, May/June, and June/July. Requested federal assistance for the most current disaster totals $17 million: $8.8 million for public assistance and $8 million for individual assistance.

The southwest quadrant of Colorado, nearly a third of the state, is experiencing severe drought. Snowpack in the San Juan Basin was 18 percent in mid-November and less than 50 percent of normal in the Upper Rio Grande Basin, while snowfall in the Denver, Boulder, and Fort Collins region has pulled those areas out of drought conditions.

As of November 19, much of Arizona’s northern half is in severe drought and three counties - Coconino, Navajo, and Apache - have been declared federal disaster areas eligible for loans.

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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