Right outsideWeather
First frost in eastern Massachusetts, and what it shows
When: September to November
A cold, calm morning can outline leaves, seed heads, webs and tracks with crystals that vanish soon after sunrise.
Why this time of year
The season's first freezes reach interior eastern Massachusetts in early-to-mid October most years, and grass-whitening frost can arrive from late September, even with the thermometer only in the mid-30s.
How to notice it
- The evening before, look for a forecast low in the mid-30s with clear skies and light wind.
- Go out within the first hour after sunrise, before sun erases the show.
- Check open grass away from buildings; the ground can run 4 to 8 degrees colder than the thermometer reading, so frost often forms before an official freeze.
- Look closely at the edges of leaves and seed heads; frost crystals grow as scales, needles, feathers, and fans.
Try this with kids: Which surfaces collect the most frost, and which stay bare?
frost forms when water vapor turns straight into ice crystals on surfaces that have cooled below freezing
Safety
- Frosted decks, steps, and boardwalks are slick; hold the rail.
Sources
- umass.edu50 percent probability first-fall 32 F dates: Worcester October 2, Middleton October 11; 36 F dates September 21 and September 27; ground temperatures can run 4-8 F below measured readings; dates vary considerably year to year.
- forecast.weather.govFrost is thin ice crystals in scales, needles, feathers, or fans; forms like dew but with surfaces below 32 F; primarily a radiational cooling event; frequently occurs with thermometer-level temperatures in the mid-30s.
- weather.govDepositional (white) frost forms when the frost point is below freezing and vapor converts directly to ice; clear skies and light winds drive the overnight surface cooling.
In the guide for September, October, November