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Tag: california drought

  • Another storm is coming to Southern California early next week. How big will it be?

    Another storm is coming to Southern California early next week. How big will it be?

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    Southern Californians can brace for another round of wet weather, with a storm expected to hit the region early next week to cap off a month of historically wet weather.

    The slow-moving storm is expected to reach the Los Angeles area by Monday night or Tuesday morning before tapering off later Tuesday, according to the National Weather Service. It’s projected to drop between a quarter of an inch and half an inch of rain in coastal areas and valleys and up to an inch in the mountains.

    The storm isn’t expected to pack the same punch as the storms earlier this month.

    “It’s considerably weaker,” said Mike Wofford, a NWS meteorologist in Oxnard. “This would be a light storm even in a fairly quiet winter pattern.”

    But because the ground is still saturated from the back-to-back historic storms earlier this month that triggered debris and mud flows, damaged homes and killed several people across the state, there’s still the risk of landslides in areas adjacent to hills. That includes the Santa Monica Mountains, the San Gabriel Mountains, the Rancho Palos Verdes area and anywhere in the Hollywood Hills.

    “Landslides can happen at any time now that the grounds are so wet,” Wofford said. “Any additional rain would make it worse. That’s something people will have to live with for a while until things dry out.”

    Downtown Los Angeles has received 17.79 inches of rain since the water year began on Oct. 1 and 12.56 inches in February alone, making it the fourth-wettest February since the weather service started keeping records in 1877. This February is also the wettest month in 26 years and is tied for the seventh-wettest month ever.

    To put things into context, downtown L.A. usually gets about 10 inches by this time in the typical water year and about 15 inches over a 12-month period.

    “If we didn’t get any rain between now and October, we’d be almost three inches above the normal for the entire year,” Wofford said. “That’s telling.”

    Following three years of severe drought, California is now experiencing one of its wettest years on record. Elsewhere in the state, the storms dropped enough snow on the Sierra Nevada to eradicate fears of a “snow drought” and build up the snowpack to 86% of normal for the date.

    California’s major reservoirs are also at 118% of their average levels for this time of year.

    “Some of the reservoirs had to do releases ahead of approaching storms so they can take in the water that falls,” Wofford said. “That’s not something we normally have to deal with in a typical winter.”

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    Summer Lin

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  • Explainer: What is an atmospheric river and how does it affect drought in California?

    Explainer: What is an atmospheric river and how does it affect drought in California?

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    Atmospheric rivers get talked about a lot during winter in California — and for good reason.

    The invisible rivers in the sky play a significant role in how much rain the state receives and can contribute to some of California’s wettest winters on record.

    But what exactly are they?

    What is an atmospheric river?

    Atmospheric rivers are long, powerful portions of the atmosphere that carry lots of water from the tropical regions near the Earth’s equator towards the poles.

    They’re invisible to the naked eye — the water is moved over the ocean in the form of water vapor, not a “river” in the way we think of them on land. They tend to move through the atmosphere in streams between 250 and 375 miles wide.

    That’s about the distance between LA and San Francisco.

    That stretch moves an astonishing amount of water. Just one atmospheric river can move an average of 10.5 trillion gallons of water per day.

    The strongest atmospheric rivers can move anywhere between seven and 25 times as much water as the flow of the Mississippi River, which is the second longest river in North America and has a watershed that reaches 32 states, according to the national park service.

    According to the National Oceanic and Atmospheric Administration, atmospheric rivers “are a primary feature in the entire global water supply and flood risks, particularly in the western U.S.”

    How do atmospheric rivers form?

    A view of the Earth using a water vapor satellite shows that moisture in the atmosphere is concentrated over the equator.

    Temperatures at the equator tend to run hotter, and just like in grade-school science lessons, hotter temperatures cause water to evaporate into the atmosphere. Warmer air can also hold more water vapor.

    The circulation of the atmosphere will pull streams of moisture away from the equator forming “atmospheric rivers.” These “rivers” of moisture can be pushed towards land by weather systems.

    Atmospheric rivers play a major role in California’s rain season. 25-50% of our state’s annual precipitation is produced by atmospheric rivers. Rain and snow amounts can vary widely depending on the exact location, timing and moisture content.

    Why are storms fueled by atmospheric rivers so powerful?

    Atmospheric rivers form and move fairly close to the surface of Earth at below 10,000 feet.

    In contrast, planes spend most of their time travelling at altitudes of 30,000 feet or higher.

    This means that, once atmospheric rivers reach land, especially the coastal mountains in California, they move up in altitude from their starting point as they travel.

    As the water vapor that makes up the rivers moves up, it cools with the temperature of the atmosphere, turning into water droplets and — eventually — lots and lots of precipitation.

    What does this have to do with California’s drought?

    Atmospheric rivers come in all shapes and sizes around the globe, and while some tend to point in a mostly consistent direction — there’s one that, according to NOAA, generally comes in from Hawaii and moves towards the West Coast of the U.S. — they do get moved around with the winds like other weather phenomena.

    This upcoming weekend, for example, will start with an atmospheric river pointed at northern and central California. Scattered clouds will make their way into the SoCal area while other parts see up to 7 inches of rain.

    But as the atmospheric river moves south, the storm will bring more and more rain to our area. That’s if they move as predicted, which can be difficult.

    “Now the one note with atmospheric rivers is, because they’re kind of narrow, and they’re very dependent on the moisture coming in off the Pacific, any slight shift in position or timing could have a big impact on how much rainfall we’re looking at,” Biggar said.

    And when the drought conditions are so severe, that change in impact gets noticed.

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    Jonathan Lloyd and Maggie More

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