|National Weather Service in South Burlington,|
Vermont put out this map of expected low
temperatures tonight. Click on it to make it
big enough to read.
In the New York Adirondacks, it's a more dire freeze warning.
Here's the difference between the two advisories. Frost can form even when the measured air temperature is a bit above freezing. National Weather Service standards have people taking air temperatures five feet off the ground.
But especially on clear, calm, chilly nights, like we're expecting tonight, it can be a few degrees colder right on the ground, where your plants are than it is a few feet higher, where your face is.
So yes, your garden plants can get damaged by frost if the temperature never officially goes below freezing.
Temperatures in most areas in the frost advisory areas are expected to drop to between 32 and 36 degrees tonight, at five feet off the ground, so frost could happen, even if it doesn't freeze. Hence the frost advisory.
In the Adirondacks, it'll probably go below freezing in many valleys, so it's a freeze warning there.
This cold spell is coming right on schedule, really.
The first freeze of the season, when the temperature gets to 32 degrees five feet off the ground, is September 8 in the cold valley of West Burke, Vermont, for instance, according to the National Weather Service in South Burlington, Vermont.
I'm guessing West Burke, and other mountain valleys in the Northeast will touch 32 degrees tonight.
Other areas of northern Vermont that are under a frost advisory on average have their first fall freeze in late September.
In Vermont's Champlain Valley, which is under neither a frost nor freeze advisory tonight, usually has its first 32 degrees in the autumn around the peak of foliage season, maybe around Oct 8. It comes even later on the shores of Lake Champlain. South Hero, Vermont normally doesn't see a freeze until mid-October.
Tonight's chill could challenge record lows for Friday morning. The record low tomorrow in Burlington, Vermont is 37. In Montpelier, it's 34, and in St. Johnsbury, 33. Morning readings could come close to those figures, so we'll see.
It'll warm up some after Friday morning, and there's no chance of frost again until perhaps Sunday night, and even that won't be as widespread as tonight.