Mountain wave clouds forming from northern Virginia into central Pennsylvania. (NASA)

Readers in Howard and Baltimore counties have spotted snow flurries, and long wave-like cloud streaks have lined up from the lee of the Appalachian mountains to the Chesapeake Bay. These weather features today are brought to us - at least in part - from Lake Superior, about 1,000 miles away.

Low pressure at high altitudes over the Northeast is steering the atmospheric flow from northwest to southeast in the Mid-Atlantic. Said flow is picking up moisture from both Lakes Superior and Michigan and carrying it towards the region.

Low pressure over the Northeast is steering winds from the western Great Lakes southeast towards Washington, D.C. and Baltimore. (

As this moist flow interacts with the mountain range to our west, the air is undergoing lift and descent helping to build the streaks of clouds downwind.

Related: December 27, 2012 moutain wave clouds in Mid-Atlantic

The combination of this northwest flow and pockets of energy (or spin, vorticity) riding along it, have produced enough lift and moisture for light snow and flurries to develop mainly north of D.C.

This is not lake effect snow per se, but rather “lake enhanced” snow. In this case, while some of the moisture is originating from the lakes, the presence of the upper level energy is allowing the snow flurries to develop east of the mountains. Without that upper level support, the moisture from the Great Lakes would dry out before reaching our region.

Nice long range lake effect snow producing light snow at BWI in the DC/Baltimore area.

— Brad Panovich (@wxbrad) February 20, 2013

Because of the distance between D.C./Baltimore and the Great Lakes and, importantly, the barrier of the mountains in between, we seldom get true “lake effect” snow. The snow bands that form when cold air flows over the relatively warm waters of the Great Lakes typically fall apart before getting to us. They may redevelop in some form if there is sufficent lift in the atmosphere giving us the so-called lake enhanced snow.

Related: Recap: Lake enhanced snow streamers dust D.C. (From December, 2010)