Tornadoes touched down in Texas and Louisiana as a powerful storm system that dumped heavy snow in California pushed through the Southern Plains and into the Deep South on Thursday. The storm knocked out power to hundreds of thousands of people and forced the cancellation of hundreds of flights in to and out of the Dallas-area. Wind gusts of over 70 mph (112 kph) were reported in Texas as tornado watches were issued into Thursday night in the Dallas-Fort Worth area. National Weather Service teams planned to head out Friday to survey areas for likely tornado damage in the storm's path, which stretched from southeast Oklahoma into Texas and neighboring Arkansas and Louisiana. “If your phone’s alerted and you hear sirens, that is for wind speeds as strong as a weak tornado,” the weather service tweeted. “So treat it like one! Get inside, away from windows!” The Dallas suburb of Richardson asked residents to stop using water after the storm knocked out power to pumping stations. “Water is currently in city water storage facilities, but will run out if all customers do not immediately cease use of water, except for emergency needs only,” Richardson officials said in a statement. North of Dallas, winds brought down trees, ripped the roof off a grocery store and overturned four 18-wheelers along U.S. Highway 75. Only minor injuries were reported, police said. In Louisiana, a tornado touched down near Louisiana State University in Shreveport. More than 310,000 utility customers in Texas had no electricity as of Thursday night, according to poweroutage.us. That was down from 346,000 early in the evening. FlightAware.com reported Dallas-Fort Worth International Airport and Dallas Love Field had tallied more than 400 cancellations total, either to or from the airports. Several school districts in the Dallas-Fort Worth area canceled after-school activities and events because of the forecast. Forecasters said the storm system would continue its eastward march Friday, bringing the threat of severe weather into the Ohio and Tennessee River valleys. It was likely to produce snow across the eastern Great Lakes and New England later in the day.