Frost Dates: First and last frost dates for Tucson, 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 March 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 January 24, so we don't dare plant that early. We wait a few days and by February 18 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° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| Last 24° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| Last 28° | Feb 2 | Jan 17 | Jan 3 | Dec 16 | -- | -- | -- | -- | -- |
| Last 32° | Feb 24 | Feb 12 | Feb 3 | Jan 27 | Jan 19 | Jan 12 | Jan 2 | Dec 19 | -- |
| Last 36° | Mar 29 | Mar 16 | Mar 6 | Feb 26 | Feb 18 | Feb 11 | Feb 2 | Jan 24 | Jan 10 |
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 28.
- There is a 50% chance of being hit by a 32° frost starting around December 18
- You have a 80% chance of seeing 32° by January 17
- 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° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| First 24° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| First 28° | Dec 15 | Dec 29 | Jan 11 | Jan 31 | -- | -- | -- | -- | -- |
| First 32° | Nov 18 | Nov 28 | Dec 5 | Dec 11 | Dec 18 | Dec 24 | Jan 2 | Jan 17 | -- |
| First 36° | Nov 7 | Nov 16 | Nov 22 | Nov 28 | Dec 3 | Dec 8 | Dec 14 | Dec 20 | Dec 29 |
Data is provided by the NOAA National Centers for Environmental Information.