BOSTON – If you’re wondering why smelled like smoke from northeastern Massachusetts all the way to the Boston area Monday it was the Salem wildfires and something known as an “inversion.”
Smoke in the Boston area
Believe it or not, the sunny one, dry autumn weather was to blame if forest fires broke out in southern New England over the weekend.
The Boston area has not had any measurable rain in two weeks. The ground has become extremely dry and covered with kindling in the form of leaves and twigs. Add to that some very breezy and dry (low relative humidity) days and you have the perfect recipe for increased forest fire danger. In such conditions, only a small spark is needed to ignite a fire, which can then spread extremely quickly.
Why does it smell like fire outside?
But why do we smell the fires a few kilometers away? This has to do with a temperature “inversion” in the atmosphere.
Normally, the smoke from a ground fire simply continues to rise vertically and is eventually swept away by the winds at the upper levels of the atmosphere.
The smoky air is warmer than the air around it and would therefore continue to rise (warm air is lighter than cold air).
CBS Boston
In the case of Monday morning, however, there was a lid on the atmosphere at about 3,000 to 1,500 meters altitude. This is called an inversion.
What is inversion?
On clear and cool nights with very little wind, the heat located near the ground “radiates” upwards. This is called radiative cooling and it’s why we get so cold on clear, calm nights. Often, like Sunday evening, this causes a temperature inversion in the lower parts of the atmosphere.
So instead of the air getting colder with height, this milder air that escaped from the ground settles a few thousand feet above our heads. This essentially creates a lid on the atmosphere.
CBS Boston
This lid ensures that things like smog and smoke do not escape. The smoke from the North Shore fires was caught by this reversal and stuck at the bottom for a few thousand feet.
CBS Boston
The wind near the ground was light at night and towards morning, blowing from the northwest between 3 and 13 miles per hour. This directed the smoke (and its smell) from places like Middleton and Salem south into Boston and surrounding towns.
CBS Boston
Air quality in Massachusetts
There is good news in the short term. First, we expect the inversion to increase during the day on Monday, allowing most of the smoke to escape upward into the atmosphere.
The wind direction is also expected to change from north to east. Any remaining smoke/odor will be pushed west toward the Route 495 area between Marlboro and Lowell, but again, likely at much lower concentrations.
What we really need is some rain.
Unfortunately, there is little to expect this week with only a small chance of some sprinkles on Tuesday evening and again on Friday. Certainly not enough to alleviate the current drought in the region.
Brush fire warning
That’s why we’ll probably continue to see wildfires popping up here and there. It is imperative that everyone avoids activities that could cause fires. This also applies to any outdoor combustion. You may think you have it under control in your backyard, but the smallest spark can easily lead to an out-of-control forest fire.
