The charts on this page show the probabilities of receiving a certain temperature on a certain day. Some examples that might help:
Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
---|---|---|---|---|---|---|---|---|---|
First 16° | Oct 20 | Oct 26 | Oct 30 | Nov 2 | Nov 5 | Nov 9 | Nov 12 | Nov 16 | Nov 22 |
First 20° | Oct 11 | Oct 17 | Oct 21 | Oct 24 | Oct 27 | Oct 31 | Nov 3 | Nov 7 | Nov 13 |
First 24° | Sep 23 | Sep 28 | Oct 2 | Oct 6 | Oct 9 | Oct 12 | Oct 16 | Oct 20 | Oct 25 |
First 28° | Sep 14 | Sep 18 | Sep 21 | Sep 24 | Sep 26 | Sep 28 | Oct 1 | Oct 4 | Oct 8 |
First 32° | Sep 6 | Sep 10 | Sep 12 | Sep 14 | Sep 16 | Sep 18 | Sep 20 | Sep 23 | Sep 26 |
First 36° | Aug 18 | Aug 24 | Aug 29 | Sep 2 | Sep 6 | Sep 9 | Sep 13 | Sep 18 | Sep 24 |
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 25. 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 26, so we don't dare plant that early. We wait a few days and by June 7 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 15 | Apr 12 | Apr 9 | Apr 7 | Apr 5 | Apr 2 | Mar 31 | Mar 28 | Mar 25 |
Last 20° | May 7 | Apr 29 | Apr 24 | Apr 20 | Apr 16 | Apr 11 | Apr 7 | Apr 2 | Mar 26 |
Last 24° | May 17 | May 11 | May 6 | May 2 | Apr 28 | Apr 24 | Apr 20 | Apr 15 | Apr 8 |
Last 28° | May 26 | May 21 | May 16 | May 13 | May 10 | May 6 | May 3 | Apr 28 | Apr 23 |
Last 32° | Jun 8 | Jun 2 | May 29 | May 25 | May 22 | May 19 | May 16 | May 11 | May 6 |
Last 36° | Jun 25 | Jun 19 | Jun 14 | Jun 11 | Jun 7 | Jun 3 | May 31 | May 26 | May 20 |
Data is provided by the NOAA National Centers for Environmental Information.