Reagan National Airport is right along the Potomac River, not far from the Chesapeake Bay. Why does this airport not get "snowed in" more often?
It's that time of year again- the lake-effect snow season has begun. The lake effect is most common in the late fall or early winter, as very cold air rushes down from Canada across the relatively warm waters of the Great Lakes.
Here in the DC Metro area, we also have a relatively warm body of water, the Chesapeake Bay. We also occasionally get a plunge of sub-freezing air rushing down from the north. So, why don't we get "bay-effect snow"? Well, there are a few factors that make the Great Lakes region perfect for the lake effect snow. And, you'll see that we are missing those same factors in our area.
First of all, the Great Lakes are situated in the middle of an immense flat plain. If you look at a topographical map, you can see that the area to the immediate north and west of the Lakes doesn't have any mountain ranges. This allows Arctic airmasses to spill out of Canada unimpeded. By contrast, the Chesapeake is just downwind of the Appalachians, which provide a barrier from the very coldest air. They also create a downsloping effect, heating the air, when northwesterly winds descend toward the Bay.
Second, the Chesapeake Bay is a mixture of fresh water from the Susquehanna, Potomac, and other rivers, along with salty ocean water. The Great Lakes are totally comprised of fresh water. Salt water has a lower vapor pressure, which makes it less apt to release water molecules into the air above. So, the "lake effect machine" is less efficient over salty bodies of water.... which is one of the reasons why the Great Salt Lake doesn't produce a lot of lake effect snow for Salt Lake City in Utah.
Third, the Great Lakes are just incredibly large. While the Chesapeake is about 4,500 square miles in surface area (which is still pretty big!), Lake Michigan is an astounding 22,300 square miles... and it's not even the biggest of the Great Lakes! So, there's a massive amount of moisture to draw from, stuck in the middle of this flat expanse of land in the middle of the country.
By the way, the lake effect got off to a late start this year, due to a lack of arctic plunges in the lake-affected regions. And with very little ice cover in place now (around 5%), the lake effect "machine" should continue running for a few more weeks. With every plunge of wintry air, places like Cleveland and Buffalo can expect the snow to pile up again!