U.S. regulators are calling on Amazon to improve its procedures for dealing with severe weather like hurricanes and tornadoes that could threaten workers at its warehouses dotted across the country.The Occupational Safety and Health Administration on Tuesday sent a “Hazard Alert Letter” to the Seattle-based e-commerce giant on Tuesday following the agency’s investigation into the deadly collapse of a company warehouse in Edwardsville, Illinois in December. Six people died and another was critically injured in the tornado …