Shovels may not be needed: Dry winter typical after wet summer
More than 2 inches of rain fell in the Lake Tahoe Basin this summer, making it the 13th wettest year of the 72 years on record, according to the National Weather Service in Reno.
After crunching weather data collected at Tahoe City, the agency’s only long-term weather station at the basin, a hydrologist says the numbers indicate that in general a wet summer is followed by a dry winter. The data also indicated that a dry summer is sometimes followed by a wet winter, but the connection was not as strong.
“If you’re wondering what to expect, expect the following winter to be on the dry side … drier than average,” said Gary Barbato, a hydrologist at the weather service. “What’s forecast is an average or normal winter.”
Last year, with the heavy snows of April and May, what appeared to be a dry winter ended up as an average one. But it was proceeded by three winters with below-average snowfall, which chipped away at the level of Lake Tahoe. It could slip below its natural rim, 6,223 feet above sea level, later this fall. It fell below its rim one day last November before rains raised it back over the rim.
The rains this summer didn’t impact the lake much because of evaporation. Barbato cited one of the larger rainstorms, on Aug. 21, that raised the lake 0.75 of inch. The water evaporated in five days. But overall, the lake is higher, five-hundredths of an inch, than it was this time last year.
“We’re actually not doing too bad,” said Barbato, comparing this year to last.
Over the summer, from June to September, the lake level dropped 1.6 feet. That translates to 141,000 acre-feet of water, enough to supply a year’s worth of water to 141,000 families. During peak summer temperatures, the lake can lose up to 0.66 of an inch a day, about 6,000 acre-feet.
In 1992, the lake dropped to the lowest level the National Weather Service has recorded — 6,220.26. After the floods of 1997, the lake topped out at 6,229.4, according to Barbato.
Last winter the region experienced a slight El Ni-o, a warming of the ocean surface temperatures in the eastern equatorial Pacific. An El Ni-o is a phenomenon that can increase the number of storms that end up hitting the Sierra Nevada. The weather phenomenon is not predicted for this year.
“There’s no scapegoat,” said Kelly Redmond, a climatologist at the Western Regional Climate Center in Reno. “It’s a mixed bag. “We see elements of both of those (El Ni-o, La Ni-a) in the ocean. One thing I think we can say is that I think not having an El Ni-o improves chances of getting one good-sized storm, a wet storm.”
Winters when storms come far apart from each other is when the Desert Research Institutes’s cloud-seeding program begins operating. Sometimes seeding starts as early as October. The institute creates snow by injecting silver iodide into clouds to give moisture something to cling to.
DRI has been seeding the clouds at Tahoe with airplanes and silver iodide generators stationed atop places like Mount Rose since the 1970s. If clouds are seeded during a storm that dumps about 1 foot of snow over a period of 10 to 12 hours, the seeding can result in an extra inch of snow, said Arlen Huggins, an associate research scientist at DRI, who runs the program.
Exactly how many ice crystals — they turn into snowflakes as they fall from a cloud — the seeding program produces is part of a two-year study that will begin this year. DRI received a grant of $320,000 from the Bureau of Land Reclamation to conduct the study in the Tahoe basin and the Walker-Carson basin.
Gregory Crofton can be reached at (530) 542-8045 or by e-mail at firstname.lastname@example.org