Cold temps promising for snowpack, but Idaho’s drought outlook for 2023 unclear

By Erin Banks Rusby; Idaho Press

Snowpack at Bogus Basin in Boise, Idaho.

The normal high temperature for Boise on Nov. 9 is 52 degrees. But this year on that day, the high was just in the 30s.

Even in mid-November, Boise’s normal highs are in the 40s, said Troy Lindquist, a senior hydrologist with the National Weather Service. That said, the Treasure Valley’s recent cold weather in tandem with the snow that fell is good news for Idaho’s water supply, he said.

“That’s nearly 20 degrees below normal, for Boise, so it’s definitely going to be chilly,” Lindquist said during a meeting earlier this month about the outlook for Idaho’s water supply over the next year. “The nice thing about this is we’ve got a fast start to our snowpack.”

The snow now blanketing Idaho’s mountains should stick around as the region is unlikely to experience significant warming soon, he said.

“Hopefully we can preserve this snowpack,” Lindquist said. “That would be an awesome way to start the snow accumulation season.”

Lindquist forecasted the weeks leading up to Thanksgiving to be cold, but said “there are no strong indications of what precipitation patterns will be like during that period.”

The water outlook for the winter, spring and summer looks promising. La Niña conditions — when sea surface temperatures of the central Pacific Ocean are below average — are “firmly in place,” Lindquist said. That phenomenon tends to bring wetter, colder-than-normal weather to the Pacific Northwest, including Idaho, he said. However, that is not always the case — some La Niña years have brought normal or below-normal precipitation, and normal or above-normal temperatures, he said.

More precipitation tends to lead to more runoff, but the Boise River at Lucky Peak Dam still fell below normal for runoff in the summers of 2022 and 2021, both La Niña years, Lindquist said.

Notably, it will be the third year in a row for La Niña conditions, Lindquist said. It will only be the third time that has happened since scientists started measuring the phenomenon in 1950, he said. Previous three-year La Niña periods include 1973 to 1976, and 1998 to 2001, he said.

Not all La Niñas are created equal. In the previous 72 years, there have been 21 years of La Niña, seven of which were “strong” La Niña years, four “moderate” and 10 “weak,” Lindquist said.

The conditions are predicted to taper off somewhere in February, March, or April, Lindquist said.

Last year’s water supply outlook was a bit of a roller coaster. This time last year, Idaho’s reservoirs were about where they are now, said Erin Whorton, a hydrologist with the National Resources Conservation Service. A wet fall 2021 led to the buildup of snowpack but was followed by the third-driest January through March period on record, leading to predictions of less-than-normal runoff, including for irrigation purposes. But April and May brought rain and cool temperatures, filling many reservoirs in southwest Idaho, providing more runoff and allowing for irrigation season to end in September rather than August.

October 2022 was relatively dry and delayed reservoirs from accumulating more water, Whorton said. But reservoirs are at similar levels to where they were this time last year, which means the majority of basins need similar levels of snowpack and runoff that they needed last year, she said.

The Boise River system in particular has a good amount of carryover from last year thanks to spring rains, she said.

In southwestern Idaho, December through February is predicted to have equal chances of below-normal or above-normal temperatures and is leaning toward above-normal precipitation, according to a chart Lindquist presented from the National Weather Service and the National Oceanic and Atmospheric Administration. In the February through April and April through June periods, southwestern Idaho has equal chances of seeing below- or above-normal temperatures and below- or above-normal precipitation, he said.

From November to the end of January 2023, the majority of Idaho is predicted to emerge from drought or to have drought improve, except for a small sliver along the state’s southern border, according to a chart presented by Lindquist.

However, David Hoekema, a hydrologist with the Idaho Department of Water Resources, expressed skepticism that the water southern Idaho would get this year would be sufficient to avoid drought. Since the 1980s, every La Niña year has seen progressively less snowpack on April 1 of the year, Hoekema said, the date considered useful for forecasting spring runoff. “If we follow that historic trend, we’re definitely going to be looking at a strong possibility of historic drought,” Hoekema said.

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