I did a ground temperature test today (10-10-2015), and wasn't real surprised to see the ground temperature still being around 90F at 5 inches deep. The reason I am interested is because I want to plant onions from seed for my first time. Earlier this year, I had read about onions liking 65-75F ground temperature for germination. That left me thinking, okay, the ground is still too hot to plant onion seed. However, everything I've read about planting onion seeds in my area is to plant them in October.
Tomorrow and Monday's forecast is 96F locally and highs in the 90s the whole week. I'm thinking I'll wait to plant onion seeds a couple weeks to see if Autumn is actually going to happen this year or not. I looked at a few sites and found this useful chart and info
http://tomclothier.hort.net/page11.html