What is a heat dome? How will it impact the DC region?

A heat dome is a ridge of high pressure that traps hot air like a lid on a pot, pushing temperatures roughly 30°F above normal and lingering for days.  Instead of letting hot air rise and disperse, the high pressure pushes it back down, compressing and warming it further, while also blocking clouds and storms that might otherwise bring relief. The result: day after day of intensifying heat with little to break the cycle.