Frost Dates: First and last frost dates for Colusa, 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 5. 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 24, so we don't dare plant that early. We wait a few days and by March 24 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 16 | Dec 31 | Dec 14 | -- | -- | -- | -- | -- | -- |
| Last 28° | Mar 2 | Feb 13 | Feb 1 | Jan 22 | Jan 12 | Jan 1 | Dec 19 | Nov 29 | -- |
| Last 32° | Apr 16 | Mar 30 | Mar 17 | Mar 7 | Feb 25 | Feb 15 | Feb 4 | Jan 22 | Jan 5 |
| Last 36° | May 5 | Apr 20 | Apr 10 | Apr 1 | Mar 24 | Mar 16 | Mar 7 | Feb 24 | Feb 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 9.
- There is a 50% chance of being hit by a 32° frost starting around November 25
- You have a 80% chance of seeing 32° by December 11
- 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 10 | Dec 27 | Jan 16 | -- | -- | -- | -- | -- | -- |
| First 28° | Nov 19 | Nov 27 | Dec 4 | Dec 9 | Dec 15 | Dec 21 | Dec 29 | Jan 11 | -- |
| First 32° | Nov 1 | Nov 9 | Nov 15 | Nov 20 | Nov 25 | Nov 30 | Dec 5 | Dec 11 | Dec 20 |
| First 36° | Oct 14 | Oct 22 | Oct 28 | Nov 3 | Nov 7 | Nov 12 | Nov 17 | Nov 23 | Dec 2 |
Data is provided by the NOAA National Centers for Environmental Information.