*The dreaded “back door” cool front...can mean the difference of 30-40 degrees over a short distance, and the difference between summer and winter over a short period of time*

As is typical with “back door” cold fronts, the difference in temperatures on Saturday may be quite dramatic over a short distance. Temperatures on Saturday could hold in the 40’s across eastern MA, Maine and even upstate NY where there will be an ocean flow of air (east-to-northeast winds) and near 80 degrees in the DC-to-Philly-to-NYC corridor where there will be a continental flow (west-to-southwest). Maps courtesy NOAA, weathermodels.com

Overview

Any long-time weather forecaster in the northeastern part of the nation knows quite well to be fearful of the “back door” cool front this time of year as it can make a forecast of summer-like temperatures look rather foolish with winter-like reality instead. Indeed, the “back door” cool front is rather common in the northeastern part of the US during the months of March and April, and it can mean the difference of 30-40 degrees over a short distance, and the difference between summer and winter weather conditions over a short period of time.

In fact, there can be winter-like temperatures this Saturday in Boston, Massachusetts while a summer-like feel is as close by as Harford, Connecticut, and summer-like temperatures in New York City and New Jersey on Saturday can drop significantly by Sunday after the passage of a “back door” cool front from northeast-to-southwest. The key factor in the potential dramatic impact of the passage of a “back door” cool front this time of year is that the western Atlantic Ocean is still quite cold so a switch of low-level flow of air from a warmer continental direction to an ocean flow can result in substantial temperature swings.

Low-level winds will be the key to the temperatures this weekend with west-to-southwest flow resulting in a taste of summer and an east-to-northeast flow producing winter-like conditions. On Saturday, the warmer (continental) flow of air will win the battle in the DC-to-Philly-to-NYC corridor, but an ocean flow may produce a big temperature drop in NYC and New Jersey by Sunday. Maps courtesy NOAA, tropicaltidbits.com

Details

It is known as a “back door” cool front since it typically moves from northeast-to-southwest as opposed to the more conventional movement of a cool front in these parts from west-to-east (it comes through the “back door”). This interesting atmospheric phenomenon which weather forecasters dread to deal occurs fairly often during the months of March and April along the northeastern Atlantic seaboard; particularly, in the New England region. The “back door” cool front will usually take place when high-pressure builds across the eastern part of Canada and the clockwise flow around the anticyclone generates a low-level east-to-northeast flow along the Northeast/Mid-Atlantic coastline. The air over the still cold western Atlantic water in March and April will begin a push to the south and west and, often, will replace a warmer (continental) air mass - potentially resulting in dramatic temperature changes.

On Saturday, there will be high pressure building into the eastern part of Canada, but there will also be a second high pressure system situated near Bermuda. This second high pressure system is a key player for Saturday as the clockwise flow of air around it will promote west-to-southwest winds in places like Washington, D.C., Philadelphia and New York City. This kind of a continental wind flow will result in a surge of temperatures on Saturday likely peaking near 80 degrees all along the DC-to-Philly-to-NYC corridor.

Two key players on Saturday will be strong high pressure centered near Bermuda and another located up across central/eastern Canada. The Bermuda high is likely to win the battle between the two on Saturday producing very warm conditions in the DC-to-Philly-to-NYC corridor while the Canadian high pressure may be the main player across eastern MA and Maine generating winter-like conditions. Map courtesy NOAA, tropicaltidbits.com

Farther to the north, the Canadian high pressure system is likely to be the more dominate player in northern New England where an ocean flow of air will likely form (i.e., east-to-northeast winds). The end result of this atmospheric battle will likely be summer-like weather conditions from DC-to-Philly-to-NYC with afternoon temperatures near 80 degrees, and a winter chill in the air up across eastern Massachusetts (e.g., Boston), Maine and even upstate NY with afternoon temperatures there in the 40’s.

On Saturday night, the “back door” cool front in New England is likely to push farther to the south and west and this could bring about dramatic temperature changes in New York City and much of New Jersey as well by Sunday with the 50’s likely there during the second half of the weekend following the summer-like temperatures there on Saturday. Whether the cool ocean air makes it all the way inland into eastern PA including the Philly metro region on Sunday is still an open question, but certainly odds favor Saturday being much warmer than Sunday.

A colder-than-normal air mass moves into the northeastern states by Tuesday following the passage of a conventional cold frontal system moving from west-to-east. Map courtesy NOAA, tropicaltidbits.com

As the next (conventional) cold front approaches the northeastern states on Monday, winds may turn back to a continental (southwesterly) direction in the northeastern states and temperatures could surge again all the way north and east into New York City...and potentially even all the way into Boston. The cold front will be accompanied by some rain and there can even be some strong thunderstorm activity at least as far north as the Mid-Atlantic. The cold front then swings through the northeastern states later Monday and all the warm weather will be swept away by a much colder incoming air mass bringing reality back to the northeastern part of the country after the brief summer tease.

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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(For more information on “The Dreaded Back Door Cold Front” scroll down our Meteorology 101 page to find a video discussion).