Gloomy Weather? It Might Be A Back Door Cold Front | WeatherBug
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Gloomy Weather? It Might Be A Back Door Cold Front

August 13, 2015
By WeatherBug Meteorologist, Andrew Rosenthal

Across the Northeast every spring, the sun-filled warmth of spring can come to an abrupt halt as a chilly gloom reminiscent of autumn spreads without warning. This dramatic flip of the weather is likely caused by a "back door" cold front.

Most weather systems in the U.S. move from west-to-east, bringing warm and cold air masses across the nation. A common type of weather system is the cold front, which is a boundary between warm air and cold air. The warm air will mix with the cold air, causing clouds and showers to form along the front. During the spring, this normal motion of weather systems can be disrupted.

In spring, the Atlantic remains very chilly off the Northeast coast, and as a result the air above it remains rather cold as well. The cold air can move onshore if an area of high pressure forms in the Canadian Maritimes northeast of New England. The air flow around the high causes the chilly and damp air over the Atlantic to move westward into the Northeast. The weather system driving this push of cold air is called a "backdoor cold front," since the weather comes out of the east, appearing to come in through the region`s "back door."

Backdoor cold fronts are common from New England to Virginia, where cold Atlantic water resides close to the coast. In the Carolinas and South, the warm Gulf Stream hugs close enough to shore to prevent the cold onshore flow.

The presence of the cold, moist Atlantic air mass leads to low clouds forming along and behind the front. Scattered showers are also possible following a back door cold front, but typically the rain is limited to mist and drizzle. The biggest change is temperatures. While the temperature may be in the 70s before a backdoor front moves through, the clouds and cool air may drop the mercury into the 50s or even into the 40s.

Backdoor cold fronts can reach as little as a few miles inland or as far as several hundred miles, depending on the strength of the cold air mass being pushed inland. Often the only limitation to the westward spread of the cold front is the Appalachian Mountains, which acts as a wall. While Philadelphia sits under cloudy skies with temperatures hovering in the 40s or 50s, Pittsburgh, only 250 miles to the west beyond the Appalachians, is enjoying a bright sunny day with mild temperatures often pushing the 70-degree mark.

The gloomy weather may last a few hours or several days depending on the strength of the warm and cold air masses that are clashing. The backdoor cold front`s demise is a push of warm air from the southwest which overwhelms the heavy cold air, forcing the high further off the coast, and the cold air mass back offshore. With the return of the warm air, the clouds give way to plenty of sunshine and temperatures returning to comfortable spring levels.

If you live in the Northeast, and the forecast of bright sunny weather is interrupted by a low gloom, it might be the presence of the back door cold front.