This all began on January 21st. An Arctic High was located over the region, bringing unseasonably cold air into the Mid-Atlantic. At the same time, an area of low pressure was developing along the Texas-Louisiana border. By the next day, the low had moved off the Georgia coast. By that afternoon, it had moved into the DC metro area… with snow becoming extremely heavy across the entire region by early evening.
By the 23rd, the system had moved off shore-- but was still producing snow at rate of over an inch per hour.
Per the National Weather Service in Sterling--
"Snowfall totals in the NWS Sterling forecast area included…Washington DC: 26” at Delcarlia Reservoir, 22.4” at the National Zoo, and 21” in Adams Morgan. In central Maryland: North Potomac 38.5”, Cascade 37.5”, Frostburg 34”, Point of Rocks 35.2”, and Reisterstown 32.1”. In eastern West Virginia: Glengary 42”, Sheperdstown 40.5”, Bayard 34.5”, and Smith Crossroads 33.2”. In northern Virginia: Round Hill 36.3”, Ashburn 36”, Berryville 35”, Karo and Bull Run both 32.1”, and Hightown, Earleysville, Chantilly and Opal all 30”."