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