Tuesday’s high temperatures across the Maritimes were about 10 degrees below normal; that departure is significant.
We were not the only ones reaching for our winter coats: the mid-afternoon temperature in Boston was 8 C; their normal high is 17 C!
This weather is not pleasant, but it gives me the opportunity to brush off a weather expression that I love, but don’t get to use very often: the backdoor cold front.
That term pops up during the spring and early summer months. It is most commonly used here in Atlantic Canada and the northeast U.S. when cool, Atlantic maritime air backs in from the east or northeast and replaces warmer continental air. When the weather systems are traveling in a normal pattern, colder air arrives from the northwest. Every now and again, cold air will slide in from the northeast and that’s when the term “backdoor” is used.
This scenario can occur when the clockwise rotation around an area of high pressure brings colder air toward the south and west. It also often takes place on the northern edge of a developing area of low pressure. This week, we had both – the blocking high over the Labrador Sea and the slow-moving system that moved in from the southwest.
If you recall, temperatures were fair on Mother’s Day but as the high dug in its heels off the east coast of the Avalon, it got colder across the Maritime provinces. I should point out that while ice pellets and wet snow wafted across the Maritime provinces, it was sunny and 14 degrees in Stephenville, N.L., and 14 in Labrador City!
Depending on the season and coastal water temperatures, air flow or wind patterns often call the shots. When it comes to the weather, it can be a lot like real estate: all about location.
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Cindy Day is the chief meteorologist for SaltWire Network.