United States: Water surpluses in SW States to persist

22 March 2023

THE BIG PICTURE
The 12-month forecast ending in November 2023 indicates widespread anomalies continuing throughout the western states, as well as pockets in the southeast. Outside of the Continental U.S., Hawaii and Alaska are expected to endure intense, widespread anomalies.

Areas experiencing severe to exceptional surpluses include:

Northern to central Utah, surrounding areas near the Great Salt Lake.
Central to northeastern Nevada, with the most intense anomalies occurring northeast of Mt. Jefferson, spreading further east along the western border of Utah.
Central California, occurring throughout the Bay Area, as well as throughout the Central Coast and San Joaquin Valley.
Central Montana, near the city of White Sulphur Springs.
Western New Mexico, near the Gila National Forest. Similar anomalies continue near the Mescalero Reservation and in pockets across northeastern New Mexico.
Western and southern Colorado, intensifying in Telluride, and continuing north into western areas of the White River National Forest. Areas along the southern border of Colorado will experience pockets of similar anomalies.
Northern Nebraska, near the city of Valentine.
Northern Texas, across the Panhandle, north of the city of Amarillo.
Southwestern and southeastern Alaska, with anomalies intensifying near the Katmai National Park Reserve, spreading north through Iliamna Lake and into western coastal regions of the North Slope Borough.
Widespread throughout Hawaii, with the highest concentration of surplus throughout the islands of O’haiu, Moloka’I, and Lanai.

Extreme to exceptional deficits are expected in the following areas:

West-central Washington into western Oregon, along the Cascade Range.
Central Idaho, near the Salmon River Mountains, moving east into Northwestern Montana.
East-central North Dakota, near the Spirit Lake Reservation.
Widespread throughout Florida, with the highest concentrations in areas southwest of Gainesville and surrounding Lake Okeechobee.
Southeastern Louisiana, near the city of New Orleans.
An isolated pocket in exceptional deficits in northern New York, near the town of Canton.

Severe deficits are anticipated in:

Indiana, throughout much of the state.
Northeastern Alaska, across the Arctic National Wildlife Refuge.

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

FORECAST BREAKDOWN
The forecast through May 2023 indicates severe to extreme surpluses to continue throughout western states of the Continental U.S., including central to northeastern Nevada, central California, southeastern Idaho, northern Nebraska, and western Colorado. Similar surpluses are expected to continue in pockets throughout nearby states, such as east-central Arizona and northern Texas. Extreme to exceptional deficits are expected to emerge in west-central Wisconsin, with similar deficits persisting in Florida and in southeastern Louisiana.

Outside of the Continental U.S., widespread extreme to exceptional surpluses are expected to continue throughout Alaska, with the most intense anomalies occurring across the state’s southern and southeastern regions. In Hawaii, surpluses of similar intensity are also expected to continue.

From June through August 2023, surplus anomalies in the eastern states will persist for eastern Nevada, western Utah, southern Idaho, and southwestern New Mexico. Intense deficits in Florida are expected to lessen in intensity into normal conditions to mild deficits. Outside of the Continental U.S., Hawaii and the majority of Alaska can expect intense surpluses, except for northwestern Alaska, which can anticipate moderate to severe deficits.

The forecast for the final months – September through November 2023 – predicts that surpluses in Nevada, Utah, Idaho, New Mexico, and Hawaii will endure, with moderate to severe deficits appearing in central Michigan. Please note that WSIM forecast skill declines with longer lead times.

IMPACTS
This season’s snowpack in the Sierra Nevada region of California is at a 261 percent increase compared to previous years’ peaks. It surpassed the record of the 1982-1983 season, which submerged more than 100,000 acres of farmland and hindered the area’s agriculture production for nearly two years. Some of California’s most prolific farming areas are directly downstream of this year’s snowpack, including the San Joaquin Valley and the Tulare basin at the base of the southern Sierra, which are two of the top three agricultural counties in the United States, according to a report from the Public Policy Institute of California. Jeffrey Mount, a senior fellow at the Public Policy Institute of California’s Water Policy Center, states that the region’s reservoirs, Lake Success and Lake Kaweah, are already full due to recent storms, and unable to take on more water to prevent flooding. “It is important to understand that we are in uncharted territory,” said Mount, “the amount of water tied up in snow in the watershed is about twice the average amount of runoff in an entire year.”

While snow accumulates across California, concerns of snow droughts have risen in parts of the Northwest and southern Colorado. According to SNOTEL, snow water equivalent (SWE) in the Pacific Northwest ranges from 82% to 133% above normal levels, but dry soil moisture profiles, low streamflows, low water levels in reservoirs, and lower-than-normal water year precipitation threatens to continue or worsen drought conditions. In southern Colorado, snowpack in basins draining into the Arkansas, White, and Red Rivers is considered problematic, with SWE currently in the 10th to 20th percentile for the period of record in the Sangre De Cristo Mountains.

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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