United States: Exceptional water deficits in AR, surpluses in ID, NV

24 February 2017

The Big Picture
The 12-month forecast through October 2017 (below) indicates water deficits throughout Arkansas reaching extreme to exceptional severity in the northern half of the state. Primarily moderate deficits are forecast across much of the South in a wide band from eastern Texas swinging east and north up through southern Pennsylvania, New Jersey, and Long Island, with isolated pockets of severe deficits. Florida, too, is expected to be drier than normal. Moderate deficits are forecast for Missouri and the northern portion of Michigan’s Lower Peninsula.

Water surplus is in the forecast for a large area encompassing northern Nevada, northwest Utah, Idaho, and eastern Oregon with exceptional surplus in northern Nevada, southern Idaho, and along the Snake River. Surpluses of varying intensity are forecast for much of California but particularly Central California where severe to isolated pockets of exceptional surplus are expected.

Moderate to severe surpluses are forecast for southern Minnesota into western and southern Wisconsin and northern Iowa. Surpluses are also forecast for western and southern Colorado, and primarily moderate surpluses along the Rio Grande River in New Mexico and along the Colorado River in Arizona as well as parts of central Arizona.

Outside the contiguous US moderate deficits are forecast for western Puerto Rico. Deficits are forecast for much of Alaska and may be more intense in the east and in the southern tip of the Southeast Region. However, surpluses are forecast for the Alaska Peninsula. Extreme surpluses are forecast for the western portion of the island of Hawai’i.

Impacts
On the heels of a very dry five years California is now facing water problems of a different kind. Winter rains and accumulated snow have wreaked havoc across the state. By mid-February state reservoirs were at 122 percent of average according to the State Water Board, and snowpack in the Sierra was 174 percent of average according the the California Department of Water Resources.

A catastrophe was averted but not before 180,000 people were evacuated from communities along the Feather River downstream of the Oroville Dam, the state's highest, as torrential rains flowed out of Lake Oroville and eroded a huge pothole in the concrete spillway, forcing officials to open the emergency spillway for the first time since the dam's opening in 1968. To take pressure off the emergency spillway more water was funneled down the concrete spillway which incurred no further damage and the evacuation order was rescinded.

A flood evacuation order was issued for 14,000 residents of San Jose in mid-February as Coyote Creek overflowed, flooding homes and temporarily shutting down a portion of the 101 Freeway. The evacuation order came late, admitted the mayor - some residents' first notice was when they saw firefighters boating through their neighborhood.

The US Drought Monitor reported on February 21 that it was the first time since since August 6, 2013 that California had no "extreme" drought conditions. However, reservoirs in Southern California are still measuring significantly below capacity: Lake Cachuma 42.4 percent, Jameson Reservoir 52.5 percent, Lake Casitas 42.3 percent, and Lake Piru 31.7 percent.

Late season drought conditions across much of Alabama's crop and pastureland in 2016 forced farmers to delay or forgo planting winter grazing, leaving cattle producers low on hay and with higher feed costs. Many have elected to sell cattle rather than buy feed.

Dry conditions in Central Florida helped fuel brush fires in Orange, Seminole, Brevard, Flagler, Polk and Marion counties. A dozen homes and 100 campsites were destroyed in Polk County as fire spread through 5,000 acres and shut down several roads. Residents were evacuated from the Marion Oaks neighborhood near Dunnellon in Marion County. Heavy smoke forced closure of several state and county roads in Osceola County.

The US Army Core of Engineers is warning boaters in Arkansas of low water levels on five reservoir lakes - between 5 and 10 feet below normal - due to drought in what is normally a rainy season.

Forecast Breakdown
The 3-month maps (below) show the evolving conditions in more detail. What is readily apparent in the February through April map is the transition away from exceptional deficit (bright red) to normal (white) from the Ohio River Valley south to the Gulf, and the continued emergence of widespread surpluses in the West.

Extreme to exceptional deficits are forecast during this period for eastern Oklahoma, northern Arkansas, Missouri, and west-central Illinois. A pocket of exceptional deficit is also expected to persist in the northern part of Michigan’s Lower Peninsula. Primarily moderate deficits are forecast for northwestern Minnesota, Florida, northern Virginia, Maryland, southeastern Pennsylvania, New Jersey, Delaware, and Long Island.

Exceptional surpluses are forecast February through April for Idaho, northern Nevada, and pockets of eastern Oregon and southeastern Washington. Moderate to isolated pockets of exceptional surplus are also forecast for much of California, particularly Central California; western Montana; the Missouri River; Platte River; southern Minnesota; northern Iowa; and Wisconsin. Surpluses are forecast to emerge in northwestern Utah and along the Green and Colorado Rivers in Utah; and in western and southern Colorado, though some areas may see both surpluses and deficits.

From May through June prior deficits noted in Oklahoma, Arkansas, Missouri and Illinois will transition to near-normal conditions in Oklahoma and Illinois and to moderate deficits in Arkansas and parts of Missouri. Moderate deficits are forecast throughout Pennsylvania; in Maryland, New Jersey, and Connecticut; the western portion of Michigan’s Upper Peninsula; northwestern Minnesota; and scattered throughout the South. Aforementioned surpluses in the western US are expected to diminish in extent and intensity, though severe to exceptional surpluses will persist in Idaho and northern Nevada.

The final months of the forecast – August through October – show the emergence of deficits in the Pacific Northwest.

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