Frost Dates: First and last frost dates for superior, 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 22.
- There is a 50% chance of being hit by a 32° frost starting around September 30
- You have a 80% chance of seeing 32° by October 9
- 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 25 | Oct 31 | Nov 4 | Nov 8 | Nov 11 | Nov 14 | Nov 18 | Nov 22 | Nov 28 |
First 20° | Oct 17 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 8 | Nov 11 | Nov 16 |
First 24° | Oct 6 | Oct 12 | Oct 16 | Oct 20 | Oct 23 | Oct 27 | Oct 30 | Nov 4 | Nov 10 |
First 28° | Sep 24 | Sep 29 | Oct 4 | Oct 7 | Oct 10 | Oct 14 | Oct 17 | Oct 21 | Oct 27 |
First 32° | Sep 17 | Sep 22 | Sep 25 | Sep 28 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 13 |
First 36° | Aug 31 | Sep 6 | Sep 10 | Sep 14 | Sep 17 | Sep 20 | Sep 24 | Sep 28 | Oct 4 |
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 16. 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 18 | Apr 12 | Apr 8 | Apr 4 | Apr 1 | Mar 29 | Mar 25 | Mar 21 | Mar 15 |
Last 20° | Apr 18 | Apr 14 | Apr 11 | Apr 8 | Apr 5 | Apr 3 | Mar 31 | Mar 28 | Mar 23 |
Last 24° | May 7 | May 1 | Apr 27 | Apr 24 | Apr 20 | Apr 17 | Apr 13 | Apr 9 | Apr 3 |
Last 28° | May 14 | May 9 | May 6 | May 3 | Apr 30 | Apr 28 | Apr 25 | Apr 21 | Apr 17 |
Last 32° | May 27 | May 21 | May 18 | May 14 | May 11 | May 8 | May 5 | May 1 | Apr 26 |
Last 36° | Jun 16 | Jun 10 | Jun 6 | Jun 3 | May 31 | May 28 | May 24 | May 20 | May 15 |
Data is provided by the NOAA National Centers for Environmental Information.