Frost Dates: First and last frost dates for port washington, wi

How to read these charts for the fall
As your growing season comes to an end, the nightly temperatures for port washington, wi 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 29, and by October 29 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 October 5.
  2. There is a 50% chance of being hit by a 32° frost starting around October 17
  3. You have a 80% chance of seeing 32° by October 29
  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° Nov 7 Nov 14 Nov 18 Nov 22 Nov 26 Nov 29 Dec 3 Dec 8 Dec 14
First 20° Nov 2 Nov 8 Nov 12 Nov 16 Nov 20 Nov 23 Nov 27 Dec 1 Dec 7
First 24° Oct 25 Oct 30 Nov 2 Nov 5 Nov 8 Nov 11 Nov 14 Nov 17 Nov 22
First 28° Oct 9 Oct 15 Oct 20 Oct 23 Oct 27 Oct 30 Nov 3 Nov 7 Nov 14
First 32° Sep 29 Oct 5 Oct 10 Oct 14 Oct 17 Oct 21 Oct 24 Oct 29 Nov 4
First 36° Sep 24 Sep 28 Oct 1 Oct 4 Oct 7 Oct 9 Oct 12 Oct 15 Oct 19

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 May 24. 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 3, so we don't dare plant that early. We wait a few days and by May 11 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 1 Mar 26 Mar 22 Mar 18 Mar 15 Mar 12 Mar 8 Mar 4 Feb 27
Last 20° Apr 7 Apr 3 Mar 30 Mar 28 Mar 25 Mar 23 Mar 20 Mar 16 Mar 12
Last 24° Apr 17 Apr 13 Apr 10 Apr 7 Apr 5 Apr 2 Mar 30 Mar 27 Mar 23
Last 28° Apr 28 Apr 23 Apr 20 Apr 17 Apr 14 Apr 11 Apr 8 Apr 5 Mar 31
Last 32° May 10 May 6 May 2 Apr 29 Apr 27 Apr 24 Apr 21 Apr 18 Apr 13
Last 36° May 24 May 20 May 17 May 14 May 11 May 9 May 6 May 3 Apr 28

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