California was in an extraordinary drought a year ago. After the last rains, where are we now?

The drought situation in California is looking better this year than at the same time last year.

As of November 2021, more than 80% of California was in extreme or worse drought, compared with about 43% this year, US Drought Monitor data shows. The data is updated weekly and shows drought conditions across the country.

Except for the San Joaquin Valley, most of the state has been hit by exceptional drought conditions. This means East Bay and North Bay cities like Oakland, Napa and Walnut Creek are finally out of their worst drought designation.

The California coast has also improved significantly this year. San Francisco, Los Angeles and the Big Sur coast quickly fell from extreme to severe after recent rains. “A wet week for much of the west has helped give a boost to the start of the current water year after a slow start,” the drought monitor’s current summary shows.

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drought improvement1111

Yoohyun Jung / The Chronicle

drought improvement1111

drought improvement1111

Yoohyun Jung / The Chronicle

Source: US Drought Monitor

In recent years, La Niña weather patterns have sidelined early-season storms approaching California, but this year was different.

Towards the end of September, the state experienced a solid decline as a rainstorm drenched the Bay Area and Sierra. October was eventually dominated by fog, which replenished the redwoods and other vegetation along the Santa Cruz Mountains. And in November, a weak atmospheric flow rained, and snow showers poured into all corners of the Southern Cascades, the Tahoe area along the Sierra Nevada, the San Bernardino Mountains and the coastal mountains along Highway 1. There were also several in the Bay Area Showers last week, bringing up to an inch of rain to downtown San Francisco and almost 2 inches of rain to the East Bay hills and North Bay valleys.

Last year’s rainy season – the rainier months from autumn to spring – started with a bang as a series of atmospheric flows raise hopes of an end to the multi-year drought. However, it ended in disappointment with scant rainfall in the new year.

This year’s sudden improvements were no accident – they were largely driven by a global weather pattern drifting in the Arctic thousands of miles away. This pattern is called the Pacific North American Oscillation, or PNA. It is characterized by two phases: positive and negative.

In a positive PNA phase, a high pressure system is blocking off the coast of California, closing our storm gate. Systems that bring rain and snow are booted out and the state stays dry. In a negative phase, a low pressure area builds up off the coast and keeps the storm gate wide open. California sees storm after storm when the pattern is negative, which has dominated since September.

Data released Thursday, while better than last year, shows about 38% of the state is still experiencing an exceptional drought. Central Valley areas like Fresno, which have experienced severe drought for years, are at risk of experiencing widespread crop losses and water shortages.

The gains seen in the Bay Area and Central Valley from recent storms are expected to carry over into the remainder of the winter season. This wet pattern is likely to continue, according to The Climate Prediction Center, although conditions at La Nina could still limit how much precipitation reaches California.

Gerry Díaz (he/she) and Yoohyun Jung are contributors to Francisco Chronicle. Email: [email protected], [email protected] Twitter @geravitywave, @yoohyun_jung