Shrinking snow in California's Sierra Nevada Mountains has officials on alert
It's been a dry start to the year and that is impacting an important source for California's water supply, the snowpack. Data shows some areas in the Sierra Nevada around half of average.
As California's wet season draws near a close, one key element seems to be absent — the wet weather.
The state's wet season occurs from October to April, when typically 90 percent of the yearly precipitation total accumulates in the Sierra Nevada Mountain Range, according to AccuWeather Senior Meteorologist Dan Kottlowski.
The majority of precipitation arrives during the colder months, since there must be enough cold air to push the jet stream southward down from Alaska and Canada in order to direct storms into the West Coast.
Snowpack, the dense layers of snow that pile up on top of the Sierra, has fallen below average as a result of dwindling precipitation, raising alarms for future water supply and wildfire concerns.
In the last monthly report issued by the California Department of Water Resources (DWR) on Jan. 30, a manual snow survey found the snowpack levels to be 79 percent of what is average for the point in the season.
Department of Water Resources staff conducting the Jan. 30, 2020, snow survey at Phillips Station, CA. (California Department of Water Resources)
The snow water equivalent — the amount of water that would remain if the snowpack was melted down — was 12 inches on Feb. 13, which is reported by the California DWR to be 57 percent of average for this date.
AccuWeather Meteorologist Bill Deger said that even lower amounts of snow -- and water locked up inside -- have been measured for locations farther south along the mountain range.
The snow water equivalent in the Sierra Nevada, pictured on Feb.12, 2019, (left) vs. the same date in 2020 (right) is dramatically different. (National Weather Service)
Snowpack in the northern Sierra is hovering around 63 percent of normal, while it's lower in the central Sierra at 58 percent of normal and at 55 percent of normal in the southern Sierra.
However, the whole season didn't face the same struggles in the Sierra, Deger said, and on Jan. 1, snowpack was actually normal or above normal.
The Golden State underwent a shift in precipitation levels since mid-January, according to Deger. Below-normal levels have been observed in California since then, as the storm track was routed toward the Pacific Northwest, bringing abundant amounts of snow and rain, while leaving California largely untouched.
According to the California DWR, the snowpack from the Sierra Nevada is responsible for 30 percent of California's fresh water needs after it melts into the springs and runs into the state's reservoirs in the spring and summer.
The state has 12 reservoirs, many of which are actually filled higher than their historical averages because above-normal precipitation bombarded the state during the wet season spanning 2018-19.
According to a report published on Feb. 10 and posted on Twitter by the National Weather Service San Francisco Bay Area, Castaic Lake and Lake Perris are at the lowest, with 86 and 85 percent of their historical averages, respectively. New Melones Lake is at 137 percent of its historical average, the highest in the state.
"You can imagine that if that snowpack is below normal, there will be less water available for that supply [due to less runoff]," Deger said.
And other parts of the state are facing similar deficits in precipitation. The San Francisco Bay area is running about 6-10 inches below normal for rainfall since the start of the year, Kottlowski said.
"Forecasting of runoff is very important to reservoir operators. It helps them manage their water supplies. It also helps them manage their releases downstream, and that can help reduce flood risks," Jeremy Hill of the DWR Division of Flood Management told AccuWeather reporter Jonathan Petramala.
This dry spell at the very end of California’s wet season could be impactful later in the year, Deger said, in the form of a harsh summer for wildfires and also with the state’s water supply.
“A below-average snowpack in the Sierra this time of year will often mean a more severe wildfire season is ahead beginning in the summer, as ground and vegetation will be drier than normal going into the months that are already normally drier than the winter,” Deger said.
He said the wet season is not over yet — with a few weeks still remaining — which could potentially allow California to make up the lost precipitation. However, over the next week, there is no snow in sight.
AccuWeather Lead Long-Range Forecaster Paul Pastelok said further out, there are a few opportunities for snowfall in the rest of February and March.
The depth of the snow in the Sierra Nevada, pictured on Feb. 12, 2019, and 2020 (National Weather Service)
He said one possibility for significant snowfall comes from a storm that could make its way into Southern California around Feb. 24, which would deposit snow over the lower Sierra Nevada and some hills surrounding Los Angeles. However, it is not yet clear this will occur.
Pastelok said his data suggests above-normal snowfall for the month of March in the northern mountains. There is a lower chance of snow overall in April, but he said he "would not rule out something."
“With each passing day,” Deger said, "time is running short.”
Additional reporting by AccuWeather's Jonathan Petramala.
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