From time to time, especially during the spring months, you'll hear meteorologists talk about "Backdoor Cold Fronts" and the impact they may have on the forecast. A backdoor cold front is simply a cold front that moves south or southwest along the Atlantic seaboard and Great Lakes...most frequently during the spring. Winds behind these backdoor fronts switch east or northeast off the cooler waters of the Atlantic. These differ from a "typical" cold front, which generally move west to east across the region, with west or northwest winds behind them. During the spring months backdoor fronts can drop temperatures by more than 20 degrees in just a few hours, as their momentum is aided by the cold, maritime air-mass present over the still chilly North Atlantic waters.
Here is an example and the progression of a backdoor cold front. On Day 1, the backdoor front began to advance into New England late in the day, helping to increase cloud cover and lower temperatures slightly into the 70s from Boston to Worcester, MA. Winds turned out of the east-northeast bringing cooler, maritime air off the relatively cold Atlantic Ocean. In fact, with the clouds and drizzle around on Day 2, temperatures struggled to reach 50° in Boston, which was nearly 30 degrees colder than just a few days earlier when highs were near 80°. Worcester also set a record "low-maximum" in this case on Day 2 when the high temperature only reached 47°. After the frontal passage, temperatures also fell more than 20 degrees in New York City, from a high of 86° on Day 1 to only 64° on Day 2.
By Day 3, the backdoor front pushed rather far to the west before stalling out along the Appalachian Mountains from Western New York to Western Virginia. Backdoor cold fronts are generally "shallow" in nature, with much of the colder, maritime air only extending a few thousand feet above the surface and therefore often have a very difficult time passing over the mountains. Day 3 also saw some of the coolest temperatures and thickest cloud cover along, and just to the east of the front, with most of New England actually drying out as an area of high pressure built in from the northeast. Between Days 2 and 3, high temperatures dropped from 83 to 59° at Harrisburg, PA and from 88 down to 62° in Washington, DC.
