Early Sunday morning the mercury dipped into the low to mid 30s and while these readings are above freezing this doesn't mean it wasn't cold enough for widespread frost. The air temperature is measured about 6 feet above the ground where it might be several degrees warmer than it is at ground level.
Widespread frost was reported from the northern suburbs into Northwest Indiana and while readings were only briefly down around freezing some of the more delicate plants were probably damaged. For those who like warm weather we have a legitimate shot at 80° on Wednesday.
The biggest change this upcoming week is that for the most part it will be dry. There is only an outside chance of a shower on Tuesday with a better chance of rain by next Sunday.
Phil
