Frost Dates: First and last frost dates for Donner Mem Sp, CA
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 13. 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° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| Last 24° | Jan 22 | Jan 8 | Dec 20 | -- | -- | -- | -- | -- | -- |
| Last 28° | Feb 6 | Jan 25 | Jan 16 | Jan 7 | Dec 29 | Dec 17 | -- | -- | -- |
| Last 32° | Mar 20 | Mar 5 | Feb 22 | Feb 13 | Feb 4 | Jan 27 | Jan 17 | Jan 6 | Dec 19 |
| Last 36° | Apr 13 | Apr 3 | Mar 27 | Mar 21 | Mar 15 | Mar 10 | Mar 4 | Feb 25 | Feb 15 |
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 15.
- There is a 50% chance of being hit by a 32° frost starting around December 3
- You have a 80% chance of seeing 32° by December 21
- 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° | Dec 28 | Jan 18 | -- | -- | -- | -- | -- | -- | -- |
| First 28° | Nov 27 | Dec 7 | Dec 14 | Dec 21 | Dec 29 | Jan 9 | -- | -- | -- |
| First 32° | Nov 6 | Nov 15 | Nov 22 | Nov 27 | Dec 3 | Dec 8 | Dec 14 | Dec 21 | Jan 1 |
| First 36° | Nov 2 | Nov 7 | Nov 11 | Nov 14 | Nov 17 | Nov 20 | Nov 23 | Nov 26 | Dec 1 |
Data is provided by the NOAA National Centers for Environmental Information.