‘Weather rollercoaster’: La Nina patterns hard to predict, Tahoe could see another dry winter
TRUCKEE, Calif. — Flashback to the day after Christmas 2021 — traffic is backed up as all but one road out of the Lake Tahoe Basin is closed as snow dumps nonstop. Over the next few days, the basin would receive record snowfall, and nothing in the following weeks.
Prepare, because as La Nina conditions form off the Pacific Coast, forecasters are saying we could be in for another similar winter.
“This time of year is, unfortunately, a lot like the last two years,” said Bryan Allegretto, Partner and California Snow Forecaster for OpenSnow. “That is because this year, like the last two years, a La Nina pattern is forming.”
El Nino and La Nina patterns are often used as a predictor for what winter conditions could look like. They both refer to ocean temperature anomalies off the Pacific coast of South America.
According to Paul Fremeau, atmospheric scientist for WeatherExtreme Ltd., El Ninos are associated with warmer than average ocean temperatures, while La Ninas are associated with colder temperatures.
“This year, La Nina is already solidly in place and will influence, at the very least, the beginning of winter,” Fremeau said.
The Farmers’ Almanac is calling for storms starting Nov. 1 and lasting through the month.
The problem for Lake Tahoe’s forecast is that it lies right where El Nino patterns coming from the South and La Nina patterns coming from the North end.
“The far Pacific Northwest often sees an uptick in precipitation during La Nina winters, while the Southwestern U.S. is typically drier than usual. Impacts for our area are relatively unpredictable from an El Nino/La Nina perspective, especially under the influence of climate change,” Fremeau said.
Last year is a perfect example of how La Nina storms end at, or near, Lake Tahoe. According to Allegretto, Tahoe came in at about 104% of average at the Snow Lab which is on the north side of the lake, while South Shore ski resorts reported about 75% of average.
The last two years have been La Nina years but the two winters looked very different. The 2020-21 winter had a spattering of storms throughout the winter but stayed below average for basically the whole season.
“Last year was a little more typical of La Nina where we had some big atmospheric river events with long dry spells in the middle,” Allegretto said, adding the La Nina storms tend to happen at the beginning and end of the season, which is what the 2021-22 season did.
Allegretto has been tracking ocean temperatures around the globe and is seeing indications that the season is likely to be drier than we’d hope.
The Farmer’s Almanac is seeing similar trends, predicting that the Southwest region, which Tahoe is included in, will see mild temperatures and drier than normal conditions.
The Old Farmers’ Almanac, on the other hand, is calling for “warmer and wetter than normal, with above-normal mountain snows,” showing the difficulty in predicting winter.
“The coldest temperatures will occur in mid-November, mid-January, and early February. The stormiest periods will be in mid- to late December, early and late January, early and late February, and late March,” the Old Farmers’ Almanac website states.
The National Weather Service Reno is looking back at past examples of three La Nina seasons in a row.
“There are only two other instances where we saw La Niñas occur in a row,” said Dustin Norman, senior meteorologist for NWS – Reno in a report. “However, not all La Niñas are created equally. Strong events typically provide us with a better, more reliable signal. This upcoming winter, we are expected to see a weak La Niña. With this in mind, we can look back at the winter of 2000-2001, a time that also saw a weak La Niña on its third year.
“Because it was a weak event, we saw almost no predictability in the precipitation pattern across much of the U.S, and a reversal in some instances,” the report continued.
One thing Allegretto sees working in the snowsports enthusiasts favor is a trend of the storms we get being colder.
“It is normal in La Nina to have colder storms so while the state could probably still run a drought and have below average precipitation, the colder nature of the storms should help bring higher snowfall than rainfall,” Allegretto said.
Fremeau puts more faith in the National Oceanic and Atmospheric Administration’s prediction models which are leaning towards a slightly warmer winter with slightly below average precipitation patterns.
“This forecast doesn’t rule out a few really good storms for Tahoe, so don’t despair,” Fremeau said. “Looking further into the future, our changing climate makes the extremes, both snowy and dry, more likely, so could be on a bit of a weather rollercoaster for the foreseeable future.”
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