Frost Dates: First and last frost dates for virginia city, 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 19. 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 21, so we don't dare plant that early. We wait a few days and by July 2 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° May 2 Apr 26 Apr 21 Apr 17 Apr 13 Apr 9 Apr 5 Mar 31 Mar 25
Last 20° May 13 May 7 May 3 Apr 29 Apr 26 Apr 23 Apr 19 Apr 15 Apr 10
Last 24° May 22 May 16 May 11 May 8 May 4 May 1 Apr 27 Apr 23 Apr 17
Last 28° Jun 20 Jun 13 Jun 8 Jun 4 May 31 May 27 May 22 May 17 May 10
Last 32° Jul 6 Jun 29 Jun 25 Jun 21 Jun 18 Jun 14 Jun 10 Jun 6 May 30
Last 36° Jul 19 Jul 13 Jul 9 Jul 5 Jul 2 Jun 29 Jun 25 Jun 21 Jun 16

How to read these charts for the fall
As your growing season comes to an end, the nightly temperatures for virginia city, 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 20, and by September 20 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 August 26.
  2. There is a 50% chance of being hit by a 32° frost starting around September 8
  3. You have a 80% chance of seeing 32° by September 20
  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 6 Oct 12 Oct 16 Oct 19 Oct 23 Oct 26 Oct 30 Nov 3 Nov 9
First 20° Sep 26 Oct 1 Oct 5 Oct 9 Oct 12 Oct 15 Oct 19 Oct 23 Oct 29
First 24° Sep 12 Sep 18 Sep 22 Sep 26 Sep 30 Oct 3 Oct 7 Oct 12 Oct 18
First 28° Sep 4 Sep 9 Sep 12 Sep 15 Sep 18 Sep 21 Sep 23 Sep 27 Oct 2
First 32° Aug 20 Aug 26 Aug 31 Sep 4 Sep 8 Sep 11 Sep 15 Sep 20 Sep 27
First 36° Aug 10 Aug 16 Aug 21 Aug 25 Aug 29 Sep 1 Sep 5 Sep 10 Sep 17

Frost Dates for other nearby locations
  • Ennis, MT
  • Alder, MT
  • Norris Madison Ph, MT
  • Twin Bridges, MT
  • Dillion U Of Montana Western, MT
  • Lakeview, MT
  • Hebgen Dam, MT
  • Glen, MT
  • Trident, MT
  • Butte Bert Mooney, MT

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