United States: Water surpluses forecast to increase in central Gulf Coast

25 July 2017

The Big Picture
The 12-month forecast through March 2018 (above) indicates a pattern of water conditions very similar to the 12-month forecast reported last month with one noticeable difference: current projections show the presence of significant water surpluses in southern Mississippi and in Alabama where normal conditions were previously forecast.

Widespread and exceptional surpluses are forecast throughout Idaho and radiating outward from there to pockets of neighboring states such as Nevada, Utah, Wyoming, Oregon, and Washington. Both deficits and surpluses are forecast for the Pacific Northwest and California, and some pockets of exceptional surplus along the central border of California and Nevada. Moving eastward, surpluses are forecast for southern Colorado, southwestern Kansas, northwestern Oklahoma, and southern Missouri, where surpluses may be especially intense. Surpluses are also forecast for: nearly all of Wisconsin, which may reach extreme to exceptional severity; Michigan’s Upper Peninsula and the northern half of Michigan’s Lower Peninsula; New York; and Vermont. Aforementioned surplus conditions in Mississippi and Alabama join a trail of water surpluses forecast from southern Louisiana reaching northeast through Mississippi, Alabama, eastern Tennessee, and western Virginia and West Virginia, which could include pockets of extreme to exceptional surplus.

Severe to exceptional water deficits are forecast for parts of the Northern Plains including eastern Montana, the Dakotas, and western Minnesota. Deficits are also forecast for Florida and coastal regions of Georgia and South Carolina.

Outside the contiguous US, deficits are forecast for Alaska and Puerto Rico, and surpluses are forecast for Hawaii.

Impacts
California declared a state of emergency in Mariposa County as a wildfire tore through 78,900 acres. Nearly 5,000 firefighters have been dispatched to the Detwiler fire near Yosemite National Park and 5,000 people were under evacuation orders. The Detwiler fire is the largest of many California wildfires fueled by hot, dry conditions in June.

The heatwave contributed to a spike in cow deaths in California's Fresno, Kings, and Tulare Counties and necessitated a temporary loosening of the rules regarding disposal of hundreds of carcasses.

Temperatures topping 100°F (38°C) for 8 consecutive days in June helped increase the rate of snowmelt, prompting engineers at Pine Flat Lake Reservoir in Tulare County to increase outflows from the reservoir into King's River and forcing downstream evacuations. The river breached its bank in Kingsburg, putting a golf course under 10 feet of water, flooding 18 recreational vehicles, and damaging 7 homes.

Drought conditions in the northern US Plains have sent wheat prices to a three-year high. At the end of June the US Drought Monitor reported 25 percent of North Dakota in extreme drought and by July 18 that figure had climbed to over 40 percent. To aid farmers in neighboring North and South Dakota suffering from lack of cattle fodder, Nebraska's governor has temporarily waived length and weight restrictions on interstate trucking. The US Department of Agriculture will allow early haying on Conservation Reserve Program acres in drought-afflicted counties in North Dakota.

Cook County joined three other Illinois counties declared disaster areas due to flooding. Heavy rainfall caused the Des Plaines and Fox Rivers to rise to record-breaking levels, at least 6,800 buildings were damaged in the northern suburbs, and floodwaters washed out a portion of highway in Lake County creating a sinkhole.

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

The near-term forecast (July through September) shows a distribution pattern of water anomalies similar to the prior three months with some decrease in the intensity of surpluses in Idaho and the Northwest, and in the intensity of deficits in Montana, the Dakotas, and western Minnesota. Surpluses are forecast to increase in extent and severity in southern Louisiana, Mississippi, and Alabama. Florida is expected to continue a transition from deficit to normal or moderate surplus conditions.

Beyond September both surplus and deficit water anomalies are projected to become less severe, though moderate deficits may re-emerge in Florida and pockets of exceptional surplus will persist in Idaho and neighboring states. The forecast for the latter months – January through March – indicates the emergence of primarily moderate surpluses in many parts of the country.

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

Note on Administrative Boundaries
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