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