Breaking news for those of you about to hop onto Metro this morning — NBCWashington.com reports that the L’Enfant Plaza Metro station has been closed due to an investigation into heavy smoke emanating from somewhere inside the station. Incoming trains are being allowed to pass through the station, but are not stopping; the investigation is also causing some back up on the Green, Blue, Orange, and Yellow Lines. At this moment, officials are unsure where the smoke is coming from. UPDATE: According to the dcfireems Twitter feed, the situation seems to be calming down, and Metro reports that the station has reopened to passengers. The fire department apparently found “no hazardous condition” — a relief since some of the reports we’ve been reading from the scene were throwing around the word “explosion.” Residual delays will continue through the morning, however.