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