Backdoor Cold Front: 40's in Late May?
From time to time, especially during the spring months, you may hear meteorologists talk about "Backdoor Cold Fronts", and the impact they have on our local weather. 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 are out of the east or northeast off the cooler ocean waters and differ from a typical cold front which generally move eastward across the region, with west or northwest winds behind them. During the spring months of March, April and May 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.
On May 27th, a backdoor cold 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 continued out of the east-northeast bringing cooler, maritime air off the relatively cold ocean waters on the 28th. In fact, with the clouds and drizzle around, temperatures struggled to reach 50° in Boston, which was nearly 30 degrees colder than just two days earlier when the high temperature reached 79°. Worcester also set a record low-maximum on the 28th when they were only able to reach 47°, which was 22 degrees below the average high of 69°! This breaks the old record low-maximum temperature of 48° for the date, which was set in 2009. After the frontal passage, temperatures also fell more than 20 degrees in New York City, from a high of 86° on the 27th to only 64° on the 28th, which is 10° below the average high for the date.
By the 29th, the backdoor frontal boundary pushed rather far to the west, 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. On the 29th, some of the coolest temperatures and thickest cloud cover was located 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. From the 28th to 29th high temperatures dropped from 83 to 59° at Harrisburg, PA and from 88 down to 62° in Washington, DC. The high temperature of 62° in Washington, DC was more than 15 degrees below average for the date, but managed to narrowly miss the all-time record low-maximum for the date, which was 60° set in 1996.