Severe thunderstorms moved across the Denver metro area and onto the eastern plains on Thursday afternoon. The main threats from Thursday's storms were hail and strong wind gusts. Heavy rainfall might produce some localized flooding as well, according to the National Weather Service in Boulder. Several severe thunderstorm warnings and a tornado warning were issued throughout the afternoon in Larimer and Weld counties. A severe thunderstorm watch was issued for northeastern Colorado until 7 p.m. with tennis ball-sized hail and tornadoes possible. Denver International Airport was on a ground stop until 5 p.m. As of 5:25 p.m., there were 616 flight delays, mostly on Southwest, United and SkyWest, according to FlightAware. After two days with Denver’s high temperature only in the low 70s, the heat is back in Colorado. Summer arrived at 2:51 p.m. MT Thursday. There is also a possibility of some moisture from Tropical Storm Alberto will drift into Colorado, enhancing some storms to severe levels, especially over northeast Colorado.