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