Frost Dates: First and last frost dates for Ashland Exp Farm, WI

How to read these charts for the fall
As your growing season comes to an end, the nightly temperatures for Ashland Exp Farm, WI start to go down, and therefore every day that goes by increases the chance that you'll get frost. Your risk of frost really begins around September 12, and by September 30 you're almost certain to have received at least one frost event.

The charts on this page show the probabilities of receiving a certain temperature on a certain day. Some examples that might help:

  1. You have a small 20% chance of getting 32° by September 16.
  2. There is a 50% chance of being hit by a 32° frost starting around September 23
  3. You have a 80% chance of seeing 32° by September 30
  4. Said another way, you have a 1 in 5 chance at making it to that day without a 32° night.
In the Fall
Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
First 16° Oct 26 Oct 30 Nov 2 Nov 5 Nov 7 Nov 10 Nov 12 Nov 16 Nov 20
First 20° Oct 14 Oct 18 Oct 22 Oct 25 Oct 27 Oct 30 Nov 2 Nov 6 Nov 10
First 24° Oct 2 Oct 7 Oct 11 Oct 15 Oct 18 Oct 21 Oct 25 Oct 29 Nov 3
First 28° Sep 19 Sep 23 Sep 26 Sep 29 Oct 2 Oct 4 Oct 7 Oct 10 Oct 15
First 32° Sep 12 Sep 16 Sep 18 Sep 21 Sep 23 Sep 25 Sep 28 Sep 30 Oct 4
First 36° Aug 28 Sep 2 Sep 6 Sep 9 Sep 12 Sep 15 Sep 18 Sep 22 Sep 27

How to read these charts for the spring
As the growing season approaches, the days get longer, the weather begins to warm up, and the nights start being less cold. You're still getting frost, but the chance of nightly frosts gets less and less with each passing day. Eventually, the frost stops, and this is when your tender plants are fully safe. So, how do you plan for this? The probabilities on this page help you assess your risk of frost on any given day.

What's a safe temperature for tender plants? When the nightly temperature falls, frost can form, even above 32°, because the air is colder high above the ground and the frost can form up there and then fall down onto your garden and do some damage, even if it's 36° on the ground. So many factors come into play, including wind, concrete, houses, trees and other structures, etc etc etc. Because of all this, you might want to consider 36° as "the danger zone".

In your average springtime, you have a 90% chance that there will be no 36° nights by June 23. In other words, you can pretty much count on being safe from frost by that day. But we want to get those tomatoes in the ground as soon as possible, right? We see that there's still an 80% chance of 36° on May 31, so we don't dare plant that early. We wait a few days and by June 9 we are at the 50/50 point. At this point, we are close and we can start watching the weather forecast. If the upcoming week's forecast doesn't show below 40°, then it's probably okay to risk planting out your plants.

In the Spring
Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Last 16° Apr 19 Apr 14 Apr 11 Apr 8 Apr 5 Apr 2 Mar 30 Mar 27 Mar 22
Last 20° May 3 Apr 28 Apr 24 Apr 21 Apr 18 Apr 15 Apr 11 Apr 8 Apr 2
Last 24° May 15 May 9 May 5 May 2 Apr 29 Apr 26 Apr 23 Apr 19 Apr 13
Last 28° Jun 1 May 26 May 22 May 19 May 16 May 13 May 9 May 5 Apr 30
Last 32° Jun 17 Jun 12 Jun 7 Jun 4 Jun 1 May 28 May 25 May 21 May 15
Last 36° Jun 23 Jun 18 Jun 14 Jun 12 Jun 9 Jun 6 Jun 3 May 31 May 26

Data is provided by the NOAA National Centers for Environmental Information.