My weather wishfulness is split this time of year. I want it to get cold so skiing will start, but I want it to stay warm so all those green tomatoes in my garden will ripen before frost.
This mental quandary led me to wonder how the date of our first frost is being affected as the climate warms and winters shrink in length. I figured it was getting later but perception is often wrong, so I asked the Northeast Regional Climate Center in Ithaca, N.Y., for data.
Surprise! There’s no obvious trend, as is shown by the poorly formatted chart at the top of this article. (Formatting is my error – Google Sheets is confusing.) It shows the date of first recorded frost at Concord Municipal Airport from 1981 (on the left) to 2019, when frost came on Oct. 5.
The average (mean) date is Sept. 27 and the range runs from Aug. 29 (wow!) in 1986 to Oct. 20 in 2005. Most of these days are just barely frosty, with low temperatures of 32 or 31 Fahrenheit.
I will add one proviso: Detecting patterns by eye is hard, and when you have a fairly small number of data points like this, changing the range can make a big difference. So this conclusion of mine should be taken with a big grain of salt.
By the way, the last frost of the season doesn’t show any pattern that I can see, either, although 2018’s record early item is startling:
Last frost of the winter at Concord, NH from 1981 (left) to 2019. Source: Northeast Regional Climate Center
This just goes to show that weather and climate are complicated. Lots of data show that our winters are getting less wintery (alas) but you don’t see it in this data point.
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Hi David, Here’s some longer-term data from the EPA on the change in length of the growing season for continuous US states. The map graphic provides a nice perspective with NH data as just a small part of a larger warming trend. Our growing season has expanded, yet not as much as some other areas.
https://www.epa.gov/climate-indicators/climate-change-indicators-length-growing-season#%20
I wish NRCC had data for Manchester. Winter temps are often remarkably warmer, given the short distance from Concord. We’ve not had a frost yet, and are not forecasted to have one within 10 days (before Nov 4).
Growing season is 11 days longer. (https://weatherspark.com/y/26350/Average-Weather-in-Manchester-New-Hampshire-United-States-Year-Round#Sections-GrowingSeason)
I suspect Concord has more inversions.
Microclimates are pretty amazing sometimes. I live down near Milford and have had one (light) frost already. But we covered the tomatoes, so we’re good!
Decadally the retreat of the first frost date is there. Using data beginning in 1981 shrouds much of the effect. Still, using your limited time series the trend is clearly toward later 1st frosts, and updating with data through 2021 would make it more obvious.
One needs to do a bit of work and go back a century to really see the trend.