Frost Dates: First and last frost dates for arrowrock dam, id
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 8. 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 May 14, so we don't dare plant that early. We wait a few days and by May 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° | Mar 8 | Mar 1 | Feb 23 | Feb 19 | Feb 14 | Feb 10 | Feb 6 | Jan 31 | Jan 24 |
Last 20° | Mar 22 | Mar 14 | Mar 8 | Mar 4 | Feb 27 | Feb 23 | Feb 18 | Feb 12 | Feb 4 |
Last 24° | Apr 11 | Apr 2 | Mar 26 | Mar 21 | Mar 15 | Mar 10 | Mar 5 | Feb 26 | Feb 17 |
Last 28° | May 2 | Apr 24 | Apr 19 | Apr 14 | Apr 10 | Apr 5 | Apr 1 | Mar 26 | Mar 18 |
Last 32° | May 20 | May 14 | May 9 | May 6 | May 2 | Apr 28 | Apr 25 | Apr 20 | Apr 14 |
Last 36° | Jun 8 | Jun 3 | May 31 | May 27 | May 24 | May 21 | May 18 | May 14 | May 9 |
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 September 26.
- There is a 50% chance of being hit by a 32° frost starting around October 6
- You have a 80% chance of seeing 32° by October 17
- 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° | Nov 13 | Nov 20 | Nov 24 | Nov 28 | Dec 2 | Dec 5 | Dec 9 | Dec 14 | Dec 20 |
First 20° | Nov 6 | Nov 11 | Nov 15 | Nov 18 | Nov 22 | Nov 25 | Nov 28 | Dec 2 | Dec 7 |
First 24° | Oct 24 | Oct 29 | Nov 3 | Nov 6 | Nov 10 | Nov 13 | Nov 17 | Nov 21 | Nov 27 |
First 28° | Oct 3 | Oct 9 | Oct 14 | Oct 18 | Oct 21 | Oct 25 | Oct 29 | Nov 3 | Nov 9 |
First 32° | Sep 21 | Sep 26 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 13 | Oct 17 | Oct 22 |
First 36° | Sep 14 | Sep 19 | Sep 22 | Sep 25 | Sep 28 | Oct 1 | Oct 4 | Oct 7 | Oct 12 |
Data is provided by the NOAA National Centers for Environmental Information.