Frost Dates: First and last frost dates for Ft Lewis, CO

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 11. 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 14, 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° May 4 Apr 27 Apr 22 Apr 18 Apr 14 Apr 10 Apr 6 Apr 1 Mar 26
Last 20° May 19 May 13 May 8 May 4 Apr 30 Apr 27 Apr 23 Apr 18 Apr 11
Last 24° Jun 6 May 30 May 26 May 21 May 18 May 14 May 10 May 5 Apr 29
Last 28° Jun 19 Jun 12 Jun 7 Jun 3 May 30 May 26 May 22 May 18 May 11
Last 32° Jun 30 Jun 25 Jun 21 Jun 17 Jun 14 Jun 11 Jun 8 Jun 4 May 29
Last 36° Jul 11 Jul 6 Jul 2 Jun 28 Jun 25 Jun 22 Jun 18 Jun 14 Jun 9

How to read these charts for the fall
As your growing season comes to an end, the nightly temperatures for Ft Lewis, CO 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 7, and by September 27 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 11.
  2. There is a 50% chance of being hit by a 32° frost starting around September 19
  3. You have a 80% chance of seeing 32° by September 27
  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 16 Oct 21 Oct 24 Oct 27 Oct 29 Nov 1 Nov 4 Nov 7 Nov 11
First 20° Oct 1 Oct 7 Oct 12 Oct 16 Oct 19 Oct 23 Oct 27 Oct 31 Nov 7
First 24° Sep 22 Sep 28 Oct 2 Oct 5 Oct 8 Oct 11 Oct 14 Oct 18 Oct 23
First 28° Sep 15 Sep 20 Sep 23 Sep 27 Sep 30 Oct 3 Oct 6 Oct 9 Oct 15
First 32° Sep 7 Sep 11 Sep 14 Sep 17 Sep 19 Sep 22 Sep 24 Sep 27 Oct 2
First 36° Aug 27 Sep 1 Sep 5 Sep 8 Sep 11 Sep 14 Sep 17 Sep 20 Sep 25

Frost Dates for other nearby locations
  • Vallecito Dam, CO
  • Aztec Ruins Nm, NM
  • Rico, CO
  • Silverton, CO
  • Mesa Verde Np, CO
  • Telluride, CO
  • Fruitland, NM
  • Cortez, CO
  • Ouray, CO
  • Hermit, CO

    Or enter a new zipcode:

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