June 15 (Reuters) - Southwest Airlines (LUV.N) began resuming flight operations across the United States late on Monday after they had been delayed for hours over a technical glitch in a weather information system, the company said. The ground stop, or halt in flights, aimed to ensure crew and customer safety as Southwest worked with a vendor of weather data to restore connectivity, an airline spokesman said in a statement. "Our third-party weather data provider experienced intermittent performance issues...preventing transmission of weather information required to safely operate our aircraft," the spokesman said in the emailed statement. Several hundred flights were affected as the glitch came near the end of the operational day, he added, but did not give the exact number. The company apologised to customers for the resulting "stress and frustration" after many complained on social media.