Severe weather threatens U.S. East Coast with possible tornadoes By Colleen Jenkins Thu Jun 13, 2013 11:53am EDT (Reuters) - A severe storm system sweeping the U.S. East Coast on Thursday delayed flights and threatened to snarl work commutes a day after causing several tornadoes, damaging hail and high winds across the upper Midwest. Thunderstorms with winds strong enough to down trees and power lines were expected from the Mid-Atlantic south into Virginia and North Carolina, and more tornadoes and hail were possible, said meteorologist Roger Edwards of the National Weather Service's Storm Prediction Center in Norman, Oklahoma. The weather service on Wednesday had described the storm system as "very dangerous" because of its potential to produce tornadoes and "derechos," storms where wind speeds increase as they move. "Today's situation doesn't look quite as intense as yesterday's, but folks who live in the Mid-Atlantic definitely shouldn't let their guard down," Edwards said. Thunderstorms were delaying flights headed to Washington, Baltimore, Philadelphia and New York, according to website FlightAware. Federal employees in Washington could choose from taking unscheduled leave or working remotely. The U.S. Open golf tournament in Ardmore, Pennsylvania, was suspended after nearly two hours of action on Thursday. Although the storm on Wednesday was not as intense as feared, it dumped 3 to 5 inches of rain in the Chicago area and caused traffic jams, train delays and flight cancellations in the third-largest U.S. city. Edwards said it was too soon to say whether a derecho had formed in the Midwest. A swath of severe weather was reported from southern Minnesota to western Pennsylvania and West Virginia. The weather service website showed more than a dozen reports of tornadoes, including in Iowa, Illinois and Ohio. Four tornadoes were reported in Wright County, Iowa, where a couple of businesses and a home were destroyed, said Stefanie Bond, spokeswoman for the state's emergency management department. The U.S. tornado season was relatively quiet until May 20, when a monster EF5 storm, the highest rating, hit the Oklahoma City suburb of Moore, killing 24 people and flattening whole sections of the town. Reporting by Colleen Jenkins; Editing by Lisa Von Ahn