Avoid being the tallest thing around. This is easy in the city, but impossible other areas. Tires have a high carbon content which renders them quite conductive. Cars are safer than bikes if lightning is about.
There have been a number of tornados spawned by thunderstorms in the DC area. If one of these forms, head for a ditch and get into it. Your chances of detecting a tornado and quickly diving for shelter are probably much better by bike than by car. Neither is as good as a safe basement.
Thunderstorms are made up of many "cells" of intense convection. Leaving as little as fifteen minutes late or early will often get you out of them. Checking radar services like Weather Underground will quickly tell you if severe weather may affect your route.
Paul