Southwest Airlines planes sit idle at Love Field in Dallas as snow falls on Feb. 4. Analysts say this winter's storms may have already cost airlines more than $6oo million. Eric Gay/AP hide caption

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Workers remove snow from the roof of a Home Depot in Methuen, Mass., on Tuesday. After a massive snowstorm, many rooftops in the Northeast were feared to be close to their weight limits. Cheryl Senter/AP hide caption

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Students Gabby Venuto (left) and Julia Cohen let off some steam during some of the expanded downtime meant to ease the stress on students at the Beaver Country Day School in Chestnut Hill, Mass. The school also eliminated AP classes a few years ago -- a bold move that administrators say hasn't hurt students' college prospects. Tovia Smith/NPR hide caption

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Heavy shipping containers like this one are used to transport molybdenum-99, a radioactive material used in diagnostic medical imaging. Courtesy of Lantheus Medical Imaging hide caption

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