Soil temperatures and those noisy cicadas

6 Storm Team Weather School

KNOXVILLE, Tenn. (WATE) — In today’s edition of Weather School, I thought it would be interesting to talk about soil surface temperatures. Why you ask? Well, let’s start with where we are. Most are in the upper 50s to right around 60°. That’s at a depth of around 4″ to 6″, almost down to 8″. Well, why is that important? These guys. We’re heading up to that 17-year cicada cycle. And this one is known as the 2021 Brood X or Brood 10 cycle that is coming up.  I’m not an entomologist, so I had to do some research on this. The reason why soil temperature is so important, at about 8″ of soil depth, they need to be around 64° or warmer for these to come out of the ground. and start to populate again across the area.  We need about 2 weeks of 70° or greater temperatures for that to happen and we haven’t quite gotten there yet as you know as we’ve still had some 60s for high temperatures. Warm rains also seeping into the ground can help accelerate this process, but we’ve not really seen that. We’ve had several cool rain events, but not really warm rain events. Another thing is when they do start to emerge it will be near trees and hedges first, because they lay their eggs on tree branches and leaves. That’s why they go down into the ground shortly after they hatch. They need temperatures around 65° to 70° to fly once they’ve been hatched and again, we’re not quite there yet either. And this whole process doesn’t last that long, because once it gets to around 88° to 93°, it’s too hot for these little guys.  So, what we’re looking at it probably is late April to mid-May before they start to come out and this whole process is only about a 6-to-8-week process. They mate, they lay eggs and once the eggs hatch, they go back into the ground for another 17 years. You’ll know it when they start to hatch, but we are still several weeks away from that.

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