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