The water line has been descending at Shasta Dam in Northern California, as a second straight dry winter is threatening to deplete reservoirs. Shasta Lake, the centerpiece of the federal Central Valley Project, was at 42% of capacity and 63% of average for the date as of Veterans Day.

Drought Developing in Much of the West

Nov 12, 2020 at 8:00am

Tim Hearden, Western Farm Press

La Nina may install a blocking ridge west of California, making for a dry winter.

La Nina conditions in the Pacific Ocean may lead to the second straight drier-than-normal winter in much of the West, as a blocking high-pressure ridge could set up off the California coast and potentially worsen an already developing drought, forecasters say.

The National Oceanic and Atmospheric Administration’s winter forecast favors warmer, drier conditions across the southern tier of the U.S. and cooler, wetter conditions in the north. This is due largely to La Nina, in which slightly below-normal sea surface temperatures lead to a high-pressure ridge that moves the storm track to the north.

The condition is marked by colder storms that can increase precipitation in the Pacific Northwest and, if the La Nina is strong enough, Northern California. But with the weak La Nina that’s expected to persist until next summer, chances are that California and the Southwest will experience another dry winter.

“For the majority in the state, more often than not La Nina conditions result in below-normal precipitation,” said Cindy Matthews, the National Weather Service’s chief forecaster in Sacramento. However, a drier-than-normal winter “does not preclude a single storm showing up and causing flooding,” she said during a recent virtual meeting with reporters.

According to the federal Climate Prediction Center, wetter-than-average conditions are likely to extend east from the Pacific Northwest, while the greatest chances for drier-than-average conditions are predicted in the Southwest, across Texas and along the Gulf Coast.

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