This is why you wait for the last frost!

When I was wondering how the National Weather Service comes up with those "last frost" dates a while back I realized with some careful manipulation of the data that it was the 90th percentile of the frost date compiled from data from the past. I even put together some charts to demonstrate it.


It turns out the last frost day (90% confident) is April 25th using the Wilmington data and April 22nd using the Porter reservoir data (a location just north of the City of Wilmington). The 50th percentile data are around April 10th.

Why is this important? Well, historically speaking, we are in still in the 50/50 range of the frost data and any one of these nights could still have a frost because only half the time in the past hundred years has the last frost occurred already. One case in point is last night, note the dip below 30 measured by the helpful KDEWILMI4 weather station website. Any plants out there would have felt freezing temperatures!

Have patience Wilmington gardeners, planting time is coming.

tags: frost, gardening, meteorology, Delaware