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