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