Frost Dates: First and last frost dates for trident, mt

How to read these charts for the spring
As the growing season approaches, the days get longer, the weather begins to warm up, and the nights start being less cold. You're still getting frost, but the chance of nightly frosts gets less and less with each passing day. Eventually, the frost stops, and this is when your tender plants are fully safe. So, how do you plan for this? The probabilities on this page help you assess your risk of frost on any given day.

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 27. 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 26, so we don't dare plant that early. We wait a few days and by June 8 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.

In the Spring
Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Last 16° Apr 12 Apr 6 Apr 1 Mar 28 Mar 25 Mar 21 Mar 17 Mar 12 Mar 6
Last 20° Apr 24 Apr 19 Apr 15 Apr 12 Apr 9 Apr 6 Apr 3 Mar 30 Mar 25
Last 24° May 4 Apr 29 Apr 25 Apr 22 Apr 19 Apr 16 Apr 13 Apr 10 Apr 5
Last 28° May 16 May 11 May 7 May 4 May 1 Apr 29 Apr 26 Apr 22 Apr 17
Last 32° Jun 13 Jun 5 May 31 May 26 May 22 May 18 May 13 May 8 Apr 30
Last 36° Jun 27 Jun 20 Jun 16 Jun 11 Jun 8 Jun 4 May 31 May 26 May 19

How to read these charts for the fall
As your growing season comes to an end, the nightly temperatures for trident, mt start to go down, and therefore every day that goes by increases the chance that you'll get frost. Your risk of frost really begins around September 6, and by September 24 you're almost certain to have received at least one frost event.

The charts on this page show the probabilities of receiving a certain temperature on a certain day. Some examples that might help:

  1. You have a small 20% chance of getting 32° by September 10.
  2. There is a 50% chance of being hit by a 32° frost starting around September 17
  3. You have a 80% chance of seeing 32° by September 24
  4. Said another way, you have a 1 in 5 chance at making it to that day without a 32° night.
In the Fall
Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
First 16° Oct 13 Oct 20 Oct 24 Oct 28 Oct 31 Nov 4 Nov 8 Nov 12 Nov 18
First 20° Oct 6 Oct 11 Oct 15 Oct 18 Oct 21 Oct 23 Oct 26 Oct 30 Nov 4
First 24° Sep 22 Sep 28 Oct 2 Oct 6 Oct 9 Oct 13 Oct 16 Oct 21 Oct 27
First 28° Sep 12 Sep 17 Sep 21 Sep 24 Sep 27 Sep 30 Oct 3 Oct 6 Oct 11
First 32° Sep 6 Sep 10 Sep 12 Sep 15 Sep 17 Sep 19 Sep 21 Sep 24 Sep 27
First 36° Aug 31 Sep 3 Sep 6 Sep 8 Sep 10 Sep 12 Sep 14 Sep 16 Sep 19

Frost Dates for other nearby locations
  • Bozeman Gallatin Fld, MT
  • Townsend, MT
  • Bozeman, MT
  • Norris Madison Ph, MT
  • Bozeman Montana St U, MT
  • Ennis, MT
  • Boulder, MT
  • Virginia City, MT
  • Helena Ap Asos, MT
  • Twin Bridges, MT

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    • Data is provided by the NOAA National Centers for Environmental Information.