The recent stretch of cold air temperatures and a lack of snow cover raised some concern for rapid increase of frost depth. Today's featured chart looks into this by presenting soil temperatures at depth from the ISU Soil Moisture Network station near Ames. This station has an infield sensor array with the shallowest depth at 14 inches (to allow for field tillage above it) and the deepest at 52 inches. The chart shows a wonderful response within the soil to the recent stretch of cold air temperatures with frost reaching the 20 inch sensor on Thursday. Even with air temperatures below 0 degrees Fahrenheit, it takes time for the soil to respond. Even with the on-going cooling, the effect of the slightly warmer weather on Wednesday can be seen with the "wave" of warming reaching 14 inches overnight into Thursday. Of course, these readings are within an agricultural field / soil. Frost depth can more quickly penetrate pavement road beds which are generally sand, rock and dry soils, which is why frost can reach depths where water lines lie and cause troubles.

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