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Operators of the nation's tallest dam prepared on Monday to shore up a crumbling emergency spillway with bags of rock while bleeding off excess water from a rain-swollen lake to ease the threat of inundating the Northern California communities under
A CLOSER LOOK

Science Behind: How record snow strained California's dam


Friday, February 17, 2017, 7:16 - Scientists say record snowfall in California's Sierra Nevada mountains is responsible for the floods that overwhelmed the country's tallest dam and forced thousands of people to have to evacuate their homes.

"That's the most snow we've seen in about the past 20 years," says NASA (National Air and Space Administration) scientist Matthew Rodell.

More snow means rising rivers and more moisture in the air. 

NASA scientists, who use satellite images to document the areas covered by snow, say they've seen a dramatic increase in snowfall in California in the past two years.

Helicopters carry rocks to the Lake Oroville Dam after an evacuation order was lifted for communities downstream in Oroville, California, U.S. February 15, 2017. REUTERS/Jim Urquhart

Spring Is Ahead! How will a developing El Niño impact our spring weather? The Spring Forecast will be released Tuesday, February 28 at 6am ET on theweathernetwork.com


A satellite image from 2015, when the snowfall was at 25 percent of normal, shows a narrow, thin column of snow cover. Two years later, that column is noticeably longer and wider. 

"They have 180 percent of normal for this time of year," Rodell says. 

Below: NASA satellite image showing 25 percent of normal snowpack over the Sierra Nevada mountain range in 2015

Below: NASA satellite image showing 180 percent of normal snowpack over the Sierra Nevada mountain range in 2017

The increase in snowfall is a direct result of a weather phenomena often referred to as the "Pineapple Express" or "atmospheric rivers." Scientists liken it to a "river in the sky" above the Sierra Nevada mountains which dumped water vapor and snow throughout the area. 

The "Pineapple Express" is created by two conditions -- strong winds and humidity from tropical areas like Hawaii.

(RELATED: Strongest storm in 6 years bears down on Southern California)

The increase in snowfall is a direct result of a weather phenomena often referred to as the "Pineapple Express" or "atmospheric rivers." Scientists liken it to a "river in the sky" above the Sierra Nevada mountains which dumped water vapor and snow throughout the area.

The "Pineapple Express" is created by two conditions -- strong winds and humidity from tropical areas like Hawaii. 

"Large amounts of precipitation and humidity move across the Pacific and hit the mountains in California and bring large amounts of precipitation and snow," Rydell says. 

While the conditions that can cause a "Pineapple Express" are clear, knowing when and where they are likely to occur is far more complicated.

Watch below: Water overflows from Oroville emergency spillway for 1st time in dam's history

"They're pretty difficult to predict from year to year…Snow cover is highly variable from month to month," Rydell says. 

While this year's surging waters strained the Oroville dam in northern California and forced thousands from their homes, Rydell says the wet weather will likely have more pluses than minuses. Most notably, it is helping with crops in a state gripped by a five-year drought.


SAFETY: Six important flood safety tips


"California's central valley produces about half of the nation's produce and when they have issues with not enough snowpack which provides a lot of the water they use for irrigation, that is a ripple effect that affects the availability of produce and the prices of the produce you see on the shelves across the country," says Rydell. 

For others living outside the "Golden State", this year's record snow could mean fresher and more abundant fruit and vegetables at the grocery store.

Watch below: Damage from February storms

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