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Atmospheric river brings abundant rainfall
snow survey
California Department of Water Resource’s staff conducts the second snow survey of 2019 in February at Phillips Station. The recent storm has added to this winter’s Sierra snowpack, which was 92 percent of normal on Monday, up from 70 percent of normal on Sunday (Photo contributed).

Stormy weather swept through the region last week and throughout Thanksgiving weekend, providing some much-needed relief after the autumn season opened with weeks of dry weather.

The Turlock area on average received over 2.5 inches of precipitation since last week, according to data provided by Turlock Irrigation District, while the Tuolumne River Watershed received over five inches — nearly an inch more than the watershed’s historical average for the entire month of November. The precipitation came after the region received just .32 inches of rain Sept. 1 through Nov. 24.

“The most recent rainfall helps to replenish the soil moisture within the watershed and locally,” TID Communications Specialist Brandon McMillan said. “Because this storm was so cold, it added to the snowpack, which will help us fill Don Pedro in spring/summer when it melts. After the recent storm, precipitation in the watershed is now 75.4 percent of average to date.”

According to the California-Nevada River Forecast Center, the Sierra snowpack is running near or above average for this time of year following the storm. As of Dec. 2, data provided by the California Cooperative Snow Surveys shows the statewide snowpack at 92 percent of normal, up from 70 percent of normal the previous day.

The storm blew in from the west, supercharged by a narrow corridor of water vapor transported through the sky. Known as an atmospheric river, or a “river in the sky” as McMillan described it, this phenomenon can be 250 to 370 miles wide. They’re fairly common in California and contribute greatly to the state’s water supply; on average, around 30 to 50 percent of water stored in the state’s snowpack comes from just a few yearly atmospheric river events. In the 2019 Water Year, Central California experienced close to 29 atmospheric rivers.

According to McMillan, there’s more rain on the way. A weak to moderate atmospheric river is forecasted to make landfall Thursday evening and last through the weekend, bringing over an inch of precipitation locally and up to four inches of rainfall in the watershed. Freezing levels for the storm are expected to be higher than the last storm at around 7,000 feet.

“After this weekend, things slow down to only a few random showers,” McMillan said.