Our cool temperatures of late will gradually warm as we build up a ridge of high pressure across the Great Basin. Local freezes will still be a possibility in the valleys Thursday and possibly Friday mornings, but high temperatures will build from the upper 60s Thursday to the mid-70s Friday, and we could hit 80 degrees over the weekend.

So how can the ground freeze when the air temperature is above freezing? To explain this, you have to understand that solid objects (like the ground, your car’s windshield, or your tomato plants) lose heat by two methods. The first is by conduction. Air of one temperature will draw heat directly from an object (we’ll use the ground) when it comes in contact with it. If there was no other energy transfer going on, the ground could always reach the ambient air temperature, but would never cool below it. In this case, frosts would never occur unless the air temperature was below freezing. But there’s a problem with this. As I said, there is more going on.

Tomorrow, I’ll talk about radiational heat transfer.