Frost Dates: First and last frost dates for Colfax, 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 May 21. 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 April 12, so we don't dare plant that early. We wait a few days and by April 27 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° | Dec 31 | -- | -- | -- | -- | -- | -- | -- | -- |
| Last 20° | Jan 6 | Dec 13 | -- | -- | -- | -- | -- | -- | -- |
| Last 24° | Feb 27 | Feb 11 | Jan 31 | Jan 20 | Jan 10 | Dec 28 | Dec 10 | -- | -- |
| Last 28° | Apr 12 | Mar 29 | Mar 18 | Mar 10 | Mar 1 | Feb 21 | Feb 12 | Feb 2 | Jan 18 |
| Last 32° | May 9 | Apr 30 | Apr 23 | Apr 17 | Apr 11 | Apr 6 | Mar 31 | Mar 24 | Mar 15 |
| Last 36° | May 21 | May 13 | May 7 | May 2 | Apr 27 | Apr 23 | Apr 18 | Apr 12 | Apr 3 |
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 2.
- There is a 50% chance of being hit by a 32° frost starting around November 15
- You have a 80% chance of seeing 32° by November 27
- 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° | Jan 22 | -- | -- | -- | -- | -- | -- | -- | -- |
| First 20° | Dec 16 | Jan 9 | -- | -- | -- | -- | -- | -- | -- |
| First 24° | Nov 19 | Dec 3 | Dec 13 | Dec 23 | Jan 2 | Jan 14 | Feb 5 | -- | -- |
| First 28° | Nov 9 | Nov 17 | Nov 23 | Nov 27 | Dec 2 | Dec 6 | Dec 11 | Dec 17 | Dec 24 |
| First 32° | Oct 26 | Nov 2 | Nov 7 | Nov 11 | Nov 15 | Nov 18 | Nov 23 | Nov 27 | Dec 4 |
| First 36° | Oct 13 | Oct 19 | Oct 24 | Oct 28 | Oct 31 | Nov 4 | Nov 8 | Nov 12 | Nov 19 |
Data is provided by the NOAA National Centers for Environmental Information.