Frost to coat parts of New England through Thursday morning

We have a couple of really cold nights coming up, prompting certain parts of New England to see their first frost of the season.Pat Greenhouse

If you still have plants outside that are not hardy, it’s time to cover them up or bring them inside. We have a couple of really cold nights coming up, prompting certain parts of New England to see their first frost of the season.

Dew points have fallen into the mid-30s over the past couple of days, an indication of Canadian air across the region. It is this dry, chilly air that allows temperatures to fall to frosty levels around sunrise each morning. Essentially, the drier the air in place, the easier heat can leave the surface, especially in October with shortening daylight. Daytime heating can escape from the surface through the atmosphere freely with less moisture available to hold heat in the lower atmosphere.

Some of us will see frost over the next couple of mornings, especially in the higher hill towns throughout New England. Many of you saw some grassy spots and plants coated in white early Tuesday and we can expect similar conditions Thursday morning, the coldest of the next several mornings. A frost may also still occur Friday morning.

Frost and freeze alerts stretch across parts of New England this evening and early Thursday morning.Boston Globe

Temperatures tonight should slip to the upper 20s and low 30s north and west of Boston. The city, South Shore and the Cape may dip into the upper 30s. The mid-30s are likely within the Worcester, Providence, and Hartford triangle.

Mid-October is very typical to see these types of mornings with cold conditions. Boston often makes it through the entire month of October without a freeze and there’s probably a better than even chance that we will do it again this year. The average date for the first frost in the city is Nov. 5.

The first frost — the date when overnight lows dip to freezing or below — typically occurs during the first half of October across Northern New England, by late October in Central New England away from the coast, and eventually along the southern portions of the region during the first week or so of November.

The average dates of first freeze and frost in the Northeast.Boston Globe

Some locations in New England that have already seen their first frost:

• Bennington, Vt. – Tuesday (31 degrees)

• Saranac Lake, Vt. - Oct. 6 (26 degrees)

• Concord, N.H. – Tuesday night (32 degrees)

• Westfield, Mass. (Springfield area) – Tuesday night (30 degrees)

• Caribou, Maine – Oct. 9 (30 degrees)

• Millinocket, Maine – Oct. 9 (32 degrees)

Since 1970, the city of Boston has seen the date of first freeze stretch to a week later, according to Climate Central. A warming climate means a longer growing season for insects and some pollen-producing plants.

The date of the first freeze in Boston has extended a week since 1970.Climate Central

Looking at the same data set across the country, the contiguous United States has seen a jump of 2.4 degrees Fahrenheit in the average temperature since 1970.

Protect those plants

If you have plants growing in the ground that you can’t bring in, covering them up will suffice. Use a light sheet draped over the plants, preferably big enough so it reaches the ground. This will keep your plants frost free.

Basil, peppers and eggplant are particularly susceptible to even a light frost. If you have carrots, beets, peas, lettuces and kale still growing, I wouldn’t worry about those. Impatiens are also susceptible to frost.

The good news is if you make it through Thursday morning with your plants still intact, I do not see a frost for at least seven days afterward. As a matter of fact, temperatures are likely to get back into the low-70s sometime this weekend and continue into early next week. This will allow things to keep growing and you may even need to water since we have not had much in the way of rainfall.