Frost Dates: First and last frost dates for Waukesha, 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 October 1.
- There is a 50% chance of being hit by a 32° frost starting around October 13
- You have a 80% chance of seeing 32° by October 24
- 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° | Nov 9 | Nov 14 | Nov 18 | Nov 22 | Nov 25 | Nov 28 | Dec 1 | Dec 5 | Dec 11 |
First 20° | Oct 30 | Nov 5 | Nov 9 | Nov 13 | Nov 16 | Nov 19 | Nov 23 | Nov 27 | Dec 3 |
First 24° | Oct 21 | Oct 25 | Oct 28 | Oct 31 | Nov 3 | Nov 5 | Nov 8 | Nov 11 | Nov 16 |
First 28° | Oct 9 | Oct 15 | Oct 19 | Oct 23 | Oct 26 | Oct 29 | Nov 2 | Nov 6 | Nov 12 |
First 32° | Sep 26 | Oct 1 | Oct 6 | Oct 9 | Oct 13 | Oct 16 | Oct 19 | Oct 24 | Oct 29 |
First 36° | Sep 20 | Sep 24 | Sep 27 | Sep 29 | Oct 2 | Oct 4 | Oct 7 | Oct 9 | Oct 14 |
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 May 28. 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 4, so we don't dare plant that early. We wait a few days and by May 13 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 3 | Mar 29 | Mar 25 | Mar 21 | Mar 18 | Mar 15 | Mar 12 | Mar 8 | Mar 2 |
Last 20° | Apr 11 | Apr 6 | Apr 2 | Mar 30 | Mar 27 | Mar 24 | Mar 20 | Mar 17 | Mar 11 |
Last 24° | Apr 17 | Apr 13 | Apr 11 | Apr 8 | Apr 6 | Apr 4 | Apr 2 | Mar 30 | Mar 26 |
Last 28° | Apr 28 | Apr 23 | Apr 20 | Apr 17 | Apr 14 | Apr 12 | Apr 9 | Apr 5 | Apr 1 |
Last 32° | May 11 | May 6 | May 3 | Apr 30 | Apr 27 | Apr 25 | Apr 22 | Apr 18 | Apr 14 |
Last 36° | May 28 | May 23 | May 19 | May 16 | May 13 | May 10 | May 7 | May 4 | Apr 29 |
Data is provided by the NOAA National Centers for Environmental Information.