Frost Dates: First and last frost dates for San Bernardino F S, 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 7. 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 2, so we don't dare plant that early. We wait a few days and by February 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° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| Last 20° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| Last 24° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| Last 28° | Feb 1 | Jan 15 | Dec 27 | -- | -- | -- | -- | -- | -- |
| Last 32° | Mar 9 | Feb 21 | Feb 10 | Jan 31 | Jan 21 | Jan 11 | Dec 28 | Dec 4 | -- |
| Last 36° | Apr 7 | Mar 25 | Mar 15 | Mar 7 | Feb 27 | Feb 20 | Feb 12 | Feb 2 | Jan 19 |
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 December 24
- 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° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| First 24° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| First 28° | Dec 18 | Dec 30 | Jan 14 | -- | -- | -- | -- | -- | -- |
| First 32° | Nov 23 | Dec 3 | Dec 11 | Dec 18 | Dec 24 | Jan 1 | Jan 11 | -- | -- |
| First 36° | Nov 7 | Nov 15 | Nov 20 | Nov 25 | Nov 29 | Dec 3 | Dec 8 | Dec 13 | Dec 21 |
Data is provided by the NOAA National Centers for Environmental Information.