The featured chart is an illustration of the interesting sub-hourly temperature variability that exists. The chart compares minute observations vs hourly temperature samples from the Cedar Rapids ISU Soil Moisture Network station back on 9 May (significant freeze event). The station reports minute averaged temperature values based on 15 second interval samples. The top panel shows the minute by minute values along with hourly sampled values from the same source data set, thus the two lines overlap at the top of each hour. The bottom panel shows the difference between the two lines with the 60 minute sample data linearly interpolated back to 1 minute interval. The difference between the two lines is rather remarkable with the most fascinating activity happening between midnight and 2 AM with the differences above 3 degrees each hour. An simple explanation is elusive at the moment, but likely due to micro-climate air flows and/or fun things happening as the air temperature dipped below freezing and various heat fluxes kicked in with the freezing of water.

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