Rain and snow to hit California in November. Will the stormy weather be enough to beat the drought?

The Bay Area and most of California have experienced a rollercoaster of active weather patterns over the past few months, from extreme heat to unusual storms and seasonal changes.

These fluctuations have been largely attributed to shifts in two global weather patterns: the Pacific North American Oscillation (PNA) and La Niña. And it looks like the PNA will rule in November. This means that the chances of low pressure systems from the Pacific Ocean bringing wet weather to California will increase over the next thirty days. That would help break the state’s ongoing drought — but not everywhere.

The coming barrage of beneficial rains and snow

A deep plume of moisture is expected to hit the Pacific Northwest early on the first day of November, and some of that moisture is likely to be absorbed by storms off the coast. Weather models are expecting a good soak in both the Pacific Northwest and Northern California. Scattered rain showers will move along the coast, while wintry weather will fall over the South Cascades and Sierra Nevada. That means most of Northern California can look forward to a healthy start to November’s rains.

This week’s highest rainfall totals — two inches or more — are likely to fall along the Sierra Nevada and Cape Mendocino coasts between Tuesday and Wednesday. But the Bay Area will also see its fair share of rain from this upcoming moisture exchange, with models leaning toward the San Francisco Peninsula getting anywhere from three-tenths of an inch along the coast to more than an inch and a half further south. Highway 1.

The Weather Forecast Center's overall outlook for winter storm impacts for Wednesday.  Most of the Sierra Nevada can look for minor risks from this storm due to slick roads and steady snowfall around three-tenths to half an inch per hour.  A milder risk of a winter storm will be possible higher in the peaks above 4,000 feet, where high winds, heavy snowpacks and low visibility will be more widespread.

The Weather Forecast Center’s overall outlook for winter storm impacts for Wednesday. Most of the Sierra Nevada can look for minor risks from this storm due to slick roads and steady snowfall around three-tenths to half an inch per hour. A milder risk of a winter storm will be possible higher in the peaks above 4,000 feet, where high winds, heavy snowpacks and low visibility will be more widespread.

Gerry Díaz / Pivotal Weather

Snow showers are also forecast to hit some of the higher elevations along the Sierra Nevada on Wednesday and Thursday of this week. Final snowfall totals will reach up to 6 inches near Tahoe, Donner Peak and many peaks around 4,000 feet before this storm moves out of the region.

Even higher totals – around 8 to 12 inches – may settle over some of the highest mountain peaks by Thursday. Fresh layers of snow ranging from a foot to an inch will be possible as far south as the Kern County Mountains, the San Bernardino Mountains and the San Jacinto Mountains extending into Baja California.

This storm system could increase the risk of landslides and debris flows on some Sierra burn scars, including the Mosquito Scar. The risk remains low for now, but it’s something we’ll keep in mind throughout the month.

Rain and snow chances during the first week of November will extend south into the Central Coast, San Joaquin Valley, LA Metro and San Diego County areas. That includes a very small chance of flurries on some of Big Sur’s highest peaks — including Pico Blanco — and trace amounts in the Angeles National Forest, the San Bernardino and San Jacintos mountains as far as Baja, California. Rainfall totals in Southern California watersheds will likely range from a tenth to a quarter of an inch when all is said and done.

All in all, November is off to a good start, with beneficial rains and snowfalls reaching most of California.

So will this momentum carry over into the rest of the month?

The extended outlook of the European model favors a negative Pacific North American Oscillation (PNA) until the month of November. This is a good indicator of an increased chance of rain for most of the month.

The extended outlook of the European model favors a negative Pacific North American Oscillation (PNA) until the month of November.  This is a good indicator of an increased chance of rain for most of the month.

The extended outlook of the European model favors a negative Pacific North American Oscillation (PNA) until the month of November. This is a good indicator of an increased chance of rain for most of the month.

Gerry Díaz / Weatherbell

But there is a catch

This PNA outlook only tells us that the storms will favor paths that take them into California. It won’t tell us if these storms have a better chance of moving into Northern California, the Sierra, Central California, or Southern California.

So forecasters are turning to the expanded model output for European, US and Canadian weather models to get an idea of ​​where high and low pressure systems will dip in the coming weeks. With recent uncertainty about La Niña’s ability to drive waves of moisture from the Pacific Ocean, there will be plenty of wiggle room.

But based on recent model guidance for the month of November, it looks like it will be a mix between mild storms — like the one we’re seeing this week forming over the Gulf of Alaska and plunging into California — and weaker storms. that scrape the California coast. No specific dates are available at this time, but the PNA status would indicate that some of the higher chances of the storm hitting the West Coast will be around the second and third weeks of November.

These weak storms will likely be able to bring “orographic lift” to the state’s coastal mountains. Orographic lift — when air is forced up through a natural barrier like a mountain range — is likely to be the biggest source of rain and snow showers across the state whenever weak storms roll in from the Pacific Ocean.

The latest drought monitor from the USDA and NOAA, with exceptional drought conditions still centered on most of the San Joaquin Valley, while extreme drought covers the Sacramento Valley, North Bay and Santa Barbara Coast.

The latest drought monitor from the USDA and NOAA, with exceptional drought conditions still centered on most of the San Joaquin Valley, while extreme drought covers the Sacramento Valley, North Bay and Santa Barbara Coast.

Gerry Díaz / US Drought Monitor

This is bittersweet for California

Storms that rely solely on orographic buoyancy typically bring uneven distribution of rain chances that leave the Central Valley bone dry.

In other words, the coast and Sierra Nevada will have a good chance to pick up moisture to help combat the drought. But the Central Valley — and especially the San Joaquin Valley — won’t be so lucky, as most of the moisture from the Pacific bypasses the center of the state. That means it won’t condense until it touches the higher peaks of the Sierra Nevada, Santa Barbara and Kern County mountains.

For now, the areas most likely to see drought conditions improve this month are North Bay Sonoma and Napa counties, the Central Coast coastal regions — including Big Sur — and the Sierra Nevada. There will also be minor improvements along stretches of Southern California, including the Santa Barbara coast and the foothills that surround the San Gabriels and Kern County mountains.

As for Northern California, the chances of showers rolling into Sonoma and Napa counties for the rest of November will depend on how many more storms manage to penetrate the moisture-rich environment.

Forecasters will continue to monitor the wet trend that weather models indicate for November. With any luck, the rain and snow showers that rolled into California in September and the late-season fog that blanketed the California coast in October are both signs that a wet environment is in store for November and potentially December. Stay tuned.

Gerry

Díaz (he/they) is a meteorologist at the San Francisco Chronicle. Email: [email protected] Twitter @geravitywave

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