It was only last week that an IEM Daily Feature denoted how anomalously warm soil temperatures had gotten after some very warm early April weather. The narrative also denoted that colder air temperatures were in the forecast and the climatology of soil temperatures would really pull values back to something closer to average. The featured chart today presents a time series of soil temperature observations from the ISU Soil Moisture station near Ames. The chart beautifully shows interesting thermal processes that happen in the soil. First you immediately notice now much more variable the four inch depth value is. This level is closest to the surface and thus more influenced by changes in air temperature and solar radiation heating. As you increase in depth, the variability decreases and you notice the lag as warming above that level works deeper into the ground with time. Even on about April 8th with four inch values starting to decline, temperatures at deeper depths were still on the rise from the warmer previous days.

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