Frost Dates: First and last frost dates for Dillion U Of Montana Western, 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 July 14. 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 June 13, so we don't dare plant that early. We wait a few days and by June 25 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 24 Apr 18 Apr 14 Apr 10 Apr 6 Apr 3 Mar 30 Mar 25 Mar 19
Last 20° May 5 Apr 29 Apr 25 Apr 21 Apr 18 Apr 15 Apr 11 Apr 7 Apr 1
Last 24° May 18 May 13 May 9 May 6 May 3 Apr 30 Apr 27 Apr 24 Apr 19
Last 28° May 29 May 25 May 22 May 19 May 16 May 13 May 11 May 7 May 3
Last 32° Jun 27 Jun 20 Jun 15 Jun 11 Jun 8 Jun 4 May 31 May 26 May 19
Last 36° Jul 14 Jul 8 Jul 3 Jun 29 Jun 25 Jun 22 Jun 18 Jun 13 Jun 7

How to read these charts for the fall
As your growing season comes to an end, the nightly temperatures for Dillion U Of Montana Western, 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 August 31, and by September 19 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 4.
  2. There is a 50% chance of being hit by a 32° frost starting around September 12
  3. You have a 80% chance of seeing 32° by September 19
  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 5 Oct 11 Oct 15 Oct 19 Oct 23 Oct 26 Oct 30 Nov 3 Nov 10
First 20° Sep 27 Oct 2 Oct 5 Oct 8 Oct 11 Oct 14 Oct 17 Oct 20 Oct 25
First 24° Sep 14 Sep 19 Sep 23 Sep 26 Sep 29 Oct 2 Oct 5 Oct 9 Oct 14
First 28° Sep 5 Sep 10 Sep 14 Sep 17 Sep 20 Sep 23 Sep 26 Sep 30 Oct 5
First 32° Aug 31 Sep 4 Sep 7 Sep 10 Sep 12 Sep 14 Sep 17 Sep 19 Sep 23
First 36° Aug 15 Aug 20 Aug 25 Aug 28 Sep 1 Sep 4 Sep 7 Sep 12 Sep 17

Frost Dates for other nearby locations
  • Glen, MT
  • Twin Bridges, MT
  • Divide, MT
  • Lima, MT
  • Alder, MT
  • Virginia City, MT
  • Butte Bert Mooney, MT
  • Jackson, MT
  • Leadore No.2, ID
  • Wisdom, MT

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