The trail is passable almost year-round. Rain is no problem, though the wind can be a doozy. In fact, it seems like the weather patterns in northern Virginia are specially calibrated to be against you inbound in the morning, and outbound in the afternoon. Some fall days after work going southbound, on the stretch parallel to the Potomac that skirts the big park where planes from Reagan National take off and land straight overhead, the wind can almost bring you to a full stop, even when you're pedaling full-force. In spring the trail is beautiful, with green leaves budding and cherry blossoms emerging, but it's a harder ride, since it fills up with people. In deep summer it clears out a bit as people go on vacation, or simply don't want to suffer in 90-degree humidity. Fall is a great time to ride, since leisure joggers and bikers have gotten tired of using the trail, and the weather is cool enough that you just barely break a sweat. But winter is probably my favorite time. Very few people use the trail in winter, especially not to commute on bike, so you have it all to yourself. Some days you may see a total of six other souls on the trail in four miles. With a facemask, gloves, toe covers, and a light jacket you are as protected from the cold as you need to be, and on the one or two worst days of the year you can wear two pairs of pants. I've never done much Chicago winter biking, and I'm not sure I'd be strong or brave enough to. But winter biking in DC is a piece of cake.
The only bummer is when it snows a few inches and stays cold. The Mount Vernon trail seems to fall under various administrative jurisdictions, such that neither Arlington County (which has a nifty bike-lane snow plow they use within city limits), the State of Virginia, the National Parks, nor the DC city government keeps it clear of snow. In a typical DC snow, weather warms up the next day or two, and the bike path melts clean within a week. But a few lasting cold spells have kept me off the bike trail for weeks at a time, as my city bike can neither navigate the soft snow nor the ridged, hard ice that forms as intrepid riders open grooves in the snow and slush with their tires, only to have it refreeze at night.
Every day as you pass Reagan airport you can watch the tides rise and fall in the holding basins dug parallel to the Potomac, seeing how high the wet mark goes, or how many rocks are visible above the water. Sometimes you'll be deafened by planes landing over your head as your path veers perpendicular to the runway at its head, or you can race planes once the trail turns 90 degrees again. You can stop to pick mulberries at the bushes just north of the runway park, or squish over them on the trail for a few months in summer. Days of rain or of heavy thaw draw your anger at the underpass of the highway, since the downspout pours right onto a low spot in the path that freezes over in the winter; clearly no consideration or regard for bikers was taken in the design of the highway. Some times you get to see Metro trains, Amtrak trains, and motor traffic pass overhead at the same time on three consecutive bridges, as the bike path is their first jump before crossing the Potomac.
As you ride the special bike bridge over the river, the cross breeze sometimes feels like it will knock you down, but it never does. If you're alone and not too self-conscious, you can whoop and yawp as you face the relentless winds. Some afternoons you can gloat to see yourself going much faster than the Interstate-bound cars on your same bridge, just past a concrete divider. On the rare occasions you get caught in a torrential summer rain, this is also the place to laugh and holler as your shoes fill up with sloshy runoff from your pant cuffs.
Now you're finally on DC soil, a fancy landing and welcome site into a network of green, sprawling parks. Be sure to salute Thomas Jefferson in his monument as you pass by. Look to your left in the morning, and at just one point you'll see him framed between two pillars, his back set square to you. Look straight ahead on the afternoon return trip, and you'll get him in profile, framed against white sky between another two pillars.
There's a massive, weeping cherry tree in a crook by the river that blossoms two weeks before all the others. Watch out for the other cherry trees lining this whole stretch like sentinels--black and bony in winter, surging slowly furry and pink in spring (every day a bit farther along), then a green, healthy monotony throughout summer before they get ratty and sheddy after their final orange hurrah in fall.
Now you're starting to get into real city turf. You can watch the condom-like scaffolding come slowly off the Washington Monument, though you must be sure to dodge the snaking lines of loafing tourists and iPad-gazers on the shared bike-pedestrian path. Watch over years as the African-American History and Culture museum, Smithsonian's newest, goes from fenced hole in the ground to concrete parking garage to jutting, angular rusted-iron skeleton to lovely lattices, a cross between flower and factory.
Get off the sidewalk here, onto the street. Sidewalk riding is prohibited in central DC, and you'll understand why when you see all the 8th-grade school visits, groups of matching T-shirts dozens strong filling up all available space. Once you get past the burgeoning humanity in the tourist districts, you can get onto well-designed bike lanes that will take you from one end of the city to another, between gleaming new luxury high-rises and molasses-slow side streets of shade-splotched hostas and families on rowhouse stoops, from bearded young white pioneers to steel-smooth strutting wool suits emanating dreams and ambition. A bike is a good vantage point to fall in love with this city.