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Polar vortex collapse's March impact
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National Grid scheme offers discounts to volunteers for saving energy
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Lake Michigan covered by stunning 'ice shards' weather phenomenon
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People burned doing 'boiling water challenge' where they try make snow
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Polar vortex to give way to dramatic warm-up after cold snap kills 21
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Mercury at record lows as deadly polar vortex spreads across US
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Mystery person pays hotel bill for 70 homeless people amid big freeze
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Chicago train tracks set on fire to keep passengers moving
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People turn boiling water into 'snow' as temperatures hit -32C
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