Frost Dates: First and last frost dates for Arlington Univ Farm, WI
The charts on this page show the probabilities of receiving a certain temperature on a certain day. Some examples that might help:
- You have a small 20% chance of getting 32° by September 15.
- There is a 50% chance of being hit by a 32° frost starting around September 25
- You have a 80% chance of seeing 32° by October 6
- Said another way, you have a 1 in 5 chance at making it to that day without a 32° night.
Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
---|---|---|---|---|---|---|---|---|---|
First 16° | Oct 20 | Oct 25 | Oct 30 | Nov 2 | Nov 6 | Nov 9 | Nov 13 | Nov 17 | Nov 23 |
First 20° | Oct 10 | Oct 16 | Oct 20 | Oct 24 | Oct 27 | Oct 30 | Nov 3 | Nov 7 | Nov 13 |
First 24° | Sep 29 | Oct 5 | Oct 10 | Oct 13 | Oct 17 | Oct 20 | Oct 24 | Oct 28 | Nov 3 |
First 28° | Sep 23 | Sep 27 | Sep 30 | Oct 3 | Oct 5 | Oct 7 | Oct 10 | Oct 13 | Oct 17 |
First 32° | Sep 9 | Sep 15 | Sep 19 | Sep 22 | Sep 25 | Sep 28 | Oct 2 | Oct 6 | Oct 11 |
First 36° | Aug 31 | Sep 6 | Sep 9 | Sep 13 | Sep 16 | Sep 19 | Sep 22 | Sep 26 | Oct 1 |
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 18. 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 20, so we don't dare plant that early. We wait a few days and by May 31 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.
Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
---|---|---|---|---|---|---|---|---|---|
Last 16° | Apr 14 | Apr 10 | Apr 7 | Apr 4 | Apr 2 | Mar 30 | Mar 28 | Mar 25 | Mar 20 |
Last 20° | Apr 23 | Apr 18 | Apr 16 | Apr 13 | Apr 11 | Apr 8 | Apr 6 | Apr 3 | Mar 30 |
Last 24° | May 4 | Apr 29 | Apr 26 | Apr 23 | Apr 20 | Apr 17 | Apr 14 | Apr 11 | Apr 6 |
Last 28° | May 18 | May 13 | May 9 | May 6 | May 3 | May 1 | Apr 27 | Apr 24 | Apr 19 |
Last 32° | Jun 8 | May 31 | May 26 | May 22 | May 18 | May 14 | May 9 | May 4 | Apr 27 |
Last 36° | Jun 18 | Jun 12 | Jun 7 | Jun 4 | May 31 | May 28 | May 24 | May 20 | May 14 |
Data is provided by the NOAA National Centers for Environmental Information.