Frost Dates: First and last frost dates for Tacna, 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 12. 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 February 25, so we don't dare plant that early. We wait a few days and by March 15 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° | Jan 1 | Dec 14 | -- | -- | -- | -- | -- | -- | -- |
| Last 24° | Jan 26 | Jan 17 | Jan 10 | Jan 4 | Dec 26 | -- | -- | -- | -- |
| Last 28° | Feb 26 | Feb 17 | Feb 10 | Feb 3 | Jan 29 | Jan 23 | Jan 17 | Jan 9 | Dec 28 |
| Last 32° | Mar 26 | Mar 15 | Mar 7 | Mar 1 | Feb 23 | Feb 17 | Feb 10 | Feb 2 | Jan 23 |
| Last 36° | Apr 12 | Apr 3 | Mar 27 | Mar 21 | Mar 15 | Mar 10 | Mar 4 | Feb 25 | Feb 16 |
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 12.
- There is a 50% chance of being hit by a 32° frost starting around November 22
- You have a 80% chance of seeing 32° by December 1
- 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 23 | -- | -- | -- | -- | -- | -- | -- | -- |
| First 24° | Dec 8 | Dec 18 | Dec 26 | Jan 3 | Jan 15 | -- | -- | -- | -- |
| First 28° | Nov 15 | Nov 24 | Nov 30 | Dec 6 | Dec 11 | Dec 16 | Dec 22 | Dec 29 | Jan 8 |
| First 32° | Nov 8 | Nov 12 | Nov 16 | Nov 19 | Nov 22 | Nov 24 | Nov 27 | Dec 1 | Dec 5 |
| First 36° | Oct 29 | Nov 2 | Nov 5 | Nov 8 | Nov 10 | Nov 13 | Nov 15 | Nov 18 | Nov 22 |
Data is provided by the NOAA National Centers for Environmental Information.