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Climate and Environment

Roads Flood, A Sinkhole Opens And People Are Ordered To Evacuate As Atmospheric River Bears Down On California

A satellite image of an atmospheric river – in the form of clouds – running into California.
An atmospheric river bringing heavy moisture to the west coast of North America on March 10, 2023.
(Courtesy NOAA
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California's latest storm brought pretty much exactly what forecasters expected: heavy bands of rain that caused intermittent flooding to Southern California.

As predicted, Santa Barbara and San Luis Obispo counties were the hardest hit, and though Los Angeles and other counties to the south look like they'll be spared from the worst, flood watches remain in effect until late Friday.

Due to the storm's impact on California, Governor Gavin Newsom declared a state of emergency across 34 counties. President Joe Biden approved an emergency disaster declaration, making federal resources available for both immediate response and recovery.

What's the weather been like?

The storm's been a bit more intense in counties north of L.A.

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The heaviest precipitation has been in San Luis Obispo County, which saw more than 10 inches of rain in one remote location.

There's been flooding in Cambria, as well as along the Los Salinas River in Los Padres National Forest. One road in Paso Robles was destroyed. A flash flood warning is in effect for the area and will remain in place until at least Friday night.

Santa Barbara – another area of concern according to the National Weather Service – also saw a bit of action, with flooding in northern parts of the county, and mudflows shutting down the 101 North in Los Alamos.

As the rain moved south throughout the day, Ventura also had some issues.

Mudflows impacted homes and a large sinkhole opened up.

The storm is expected to wrap up by early Saturday, however there are flood watches in place from Ventura to San Diego. As usual, be careful driving (or don't drive at all) as streets can easily flood, especially when storm drains back up.

Further inland, evacuations orders have been issued for lower lying areas of Kern County due to major flooding.

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Why this atmospheric river is called a 'Pineapple Express'

A "Pineapple Express" is a strong atmospheric river that pulls moisture up from the tropics, making it warmer than, say, an atmospheric river that comes down from Alaska, like what happened in late February. As a result, more the precipitation falls as rain, though we can see snow at higher elevations.

The current storm's main energy is coming over from the northern Pacific, but the jet stream that's fueling it is bringing up tropical moisture from below Hawaii.

The two are combining off the west coast of North America and slamming into us, as you can see here:

A satellite image of clouds, pulling moisture from the north and mid Pacific regions into California.
You can seen the storm's main energy coming from the northern Pacific.
(Courtesy National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration)

The warm rain brings with it a whole different set of hazards, especially to areas recently deluged by snow.

How will this affect mountain communities?

When it comes to snow-covered mountain communities, warm rain is a concern because it's awfully effective at melting snow and creating all sorts of flooding issues.

In addition to that, it adds to the weight of the snow already piled up on peoples roofs, making them more susceptible to collapse. You can learn about that here: New Storm, New Danger For Mountain Communities Watching For Roof Collapses And Flooding

That said, snowpack at higher elevations is so deep and this rain is likely light enough, that it should just get absorbed into the snow over the next 24 hours. Lower elevation snow that's been sticking around in our foothills will likely melt away.

The warmer weather is also going to increase the risk of avalanches at elevations above 5,000 feet — and, wind gusts up to 40 mph can send things flying.

Goodbye to La Niña

La Niña is now officially over, according to NOAA. The climate pattern — indicated in part by cooling waters in the equatorial Pacific — is often associated with drier conditions in Southern California, though this winter it clearly was not.

Our snowpack is at nearly 200% of normal across the Sierra and L.A.’s gotten drenched with 184% of the rain we’d expect in an average year. All the precipitation has now had a significant effect on longstanding drought conditions in the state.

Map of California at left has large sections of white, indicating no drought and nothing in shades of red. Map at left has the entire state in shades from yellow to red.
Compare drought conditions from this week (left) to the beginning of the year (right). White areas indicate no drought. Red areas are extreme drought.
(Courtesy U.S. Drought Monitor)
El Niño vs. La Niña
  • The climate patterns known as El Niño and La Niña can have substantial impacts on weather in California. They tend to develop some time around March, with one or the other coming along every three to five years, according to the National Oceanic and Atmospheric Administration.

  • But what's the difference between them? Here are the basics:

  • El Niño

    • Tends to last 9-12 months
    • Occurs when trade winds weaken, and waters in the eastern and central equatorial Pacific warm
    • Can result in wetter weather in Southern California and drier weather further north
  • La Niña

    • Can last 1-3 years
    • Indicated by cooling waters in equatorial Pacific
    • Occurs when strong trade winds build, and waters in the eastern and central equatorial Pacific cool.
    • Can result in drier weather in SoCal and wetter weather further north.

NOAA also explains that we could see El Niño start to shape up in time for our next rainy season, though it’s a bit far out to say for sure. If it does, that could theoretically mean wetter conditions than normal (what it’s often associated with), though the last time it came around in 2018, we didn’t see much standout precipitation.

The bottom line is this: Save as much water as you can, because besides hotter temperatures, we don’t know what kind of weather the next year is going to bring.

Staying safe while driving in the rain

  • Roadway safety experts advised motorists to:

    • Check weather and road conditions all along your planned route
    • Slow down
    • Keep a wider-than-usual distance between your vehicle and the one in front
    • Don't drive through standing water — as little as 12 inches of rushing water can carry away most cars, and two feet can carry away SUVs and trucks.
    • Make sure tires are fully inflated
    • Check windshield wiper blades and replace if necessary

How to stay safe in high winds

Safety tips from Southern California Edison
    • Watch for traffic signals that may be out. Approach those intersections as four-way stops.
    • Make sure you have a battery-operated radio and flashlights. Check the batteries to make sure they are fresh. Use flashlights for lighting during a power outage; do not use candles because they may pose a significant fire hazard.
    • If you’re in a vehicle with a fallen power line on it, stay in the vehicle and remain calm until help arrives. It is OK to use your cellphone to call 911. If you must leave the vehicle, remember to exit away from downed power lines and exit by jumping from the vehicle and landing with both feet together. You must not touch the vehicle and the ground at the same time. Then proceed away from the vehicle by shuffling and not picking up your feet until you are several yards away. 
    • Water and electricity don’t mix. Water is an excellent conductor of electricity. Do not step in or enter any water that a downed power line may be touching.
    • Do not use any equipment inside that is designed for outdoor heating or cooking. Such equipment can emit carbon monoxide and other toxic gases.
    • If you use a generator, place it outdoors and plug individual appliances directly into it, using a heavy-duty extension cord. Connecting generators directly to household circuits creates “backfeed,” which is dangerous to repair crews.
    • Leave the doors of your refrigerator and freezer closed to keep food as fresh as possible. Place blocks of ice inside to help keep food cold. Check food carefully for signs of spoilage. 
    • Check on your neighbors to make sure everyone is safe.

Tips to keep your heating bills down

  • State law requires residential units to have heating systems that can keep indoor temperatures at a minimum of 70 degrees. That means every dwelling unit and guest room offered for rent or lease should offer heating equipment, usually central air conditioning (A/C) or a wall heater. — Caitlin Hernández

  • Use heat smartly to save money: Cranking things like the A/C and wall heaters can be expensive. If money is tight, be judicious about how and when you use your utilities. For example, only use heaters at night or only set the thermostat to around 70 degrees.

  • Open and close those vents: If you have central A/C, look at where the vents are around your home. Are any open in places where you don’t stay long? Practice opening and closing those so warm air only goes where you need it (most vents should have a small toggle lever). Humidifiers can also help you warm things up — and it’s useful to add moisture into our dry air.

  • Adjust your wall heaters: If you have a wall heater, you can change the output by adjusting the knob (usually at the bottom). Since wall heaters can only warm the areas where they’re placed, it’s essential to close doors to rooms you won’t be in so hot air doesn’t get wasted.

  • Turn on your ceiling fan (really): If you have a ceiling fan, try turning it on. This sounds counterintuitive, but there’s science behind it. The direction a fan turns can push air in different directions, and since hot air floats up, you’ll want to move that around. Your fan should spin clockwise to create an updraft to circulate. Not all fans will have this option, though.

Additional storm resources

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