It's not so much unheard of in DC, more that we don't get enough snow to warrant heavier investment in snow removal - easier to shut down for a day or two. Anybody who sees snow in the forecast and gets on I-95 or any other major highway in the area is insane.

This site lists most major winter weather events in the DC region over the past decades... https://www.weather.gov/lwx/winter_DC-Winters