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Idaho moisture outlook better in south than north

An Idaho hydrology expert says conditions are favoring another dry winter in Northern Idaho but the possibility of good moisture in Southern Idaho.
John O’Connell

Capital Press

Published on September 28, 2015 11:30AM

Phil Morrisey, a hydrologist with USDA’s Natural Resources Conservation Service trims vegetation surrounding the SNOTEL snow measurement site at Bogus Basin in the foothills above Boise. NRCS hydrology experts predict a dry winter in Northern Idaho but optimistic Southern Idaho could still see ample moisture.

Courtesy of Natural Resources Conservation Service

Phil Morrisey, a hydrologist with USDA’s Natural Resources Conservation Service trims vegetation surrounding the SNOTEL snow measurement site at Bogus Basin in the foothills above Boise. NRCS hydrology experts predict a dry winter in Northern Idaho but optimistic Southern Idaho could still see ample moisture.


BOISE — At the start of a new water year, oceanic conditions indicate Northern Idaho farmers will face another dry winter, said Ron Abramovich, water supply specialist with USDA’s Natural Resources Conservation Service.

But the Southern Idaho outlook is much hazier, and history tells Abramovich not to rule out an above-normal snowpack for the region.

The National Oceanic and Atmospheric Administration projects all of the state will experience above-normal temperatures and a likelihood of below-normal precipitation this winter, with the odds of dry weather progressively increasing further north in the state.

“I’m a little more optimistic (for Southern Idaho),” Abramovich said. “I’m leaning more toward the wetter side than the drier side.”

Abramovich explained a strong El Nino pattern has developed — characterized by warm water stretching from the mid-Pacific to South America along the equator — and trade winds have held the water in place.

Abramovich analyzed a dozen strong El Nino years of the past, finding half the time, Southern Idaho experienced above-normal snowpack. Elsewhere in the state, however, a strong El Nino pattern translated to below-average moisture 90 percent of the time. He said the current pattern represents the strongest El Nino since 1983, which was an exceptional water year in Southern Idaho.

Under a strong El Nino, Abramovich said, storms often track from California and enter Southern Idaho from the Owyhee Basin, where growers have faced extreme shortages in recent years.

Lynn Tominaga, executive director of Idaho Ground Water Appropriators, Inc., who closely follows winter weather patterns to base water leasing decisions, is also optimistic.

“Right now, the outlook (for Southern Idaho) is neutral. It doesn’t say anything,” Tominaga said, “If it stays neutral, we should probably have a normal winter.”

The wild card, Abramovich said, is the Pacific Decadal Oscillation — a pocket of warm water stretching from Alaska to Mexico known to force the jet streams around the Pacific Northwest, leading storms to miss the region. Abramovich said the pattern still track storms along the Continental Divide, adding snowpack to the headwaters of the Upper Snake Basin. Furthermore, in 1997, the Pacific Decadal Oscillation reversed itself prior to winter in the presence of a strong El Nino.

“It’s going to be a battle this winter between the warm spot, if it remains, or El Nino, as to which one determines our fate,” Abramovich said.

For the water year ending Oct. 1, moisture in the Payette and Salmon basins and throughout Northern Idaho ranged from 81 to 89 percent of normal, with some snow survey sites near Priest Lake at their driest levels in 75 years. Precipitation ranged from 90 to 110 percent of normal throughout Southern Idaho, though Abramovich explained some regions, such as Owyhee Basin, experienced shortages nonetheless, due to moisture falling as rain rather than snow.

This fall, Abramovich said growers east of Twin Falls have mostly received ample precipitation.

“This last storm we had we got well over 2.5 inches of rain,” said Sid Cellan, a dryland farmer in Eastern Idaho’s Caribou County whose fall wheat has already emerged and appears healthy. “We’re way above average rainfall.”

Abramovich said growers elsewhere in the state may have to make up soil moisture deficits in the spring.



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