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Monthly Science: Well Pit Temperature
With more data, those February lows really stand out:

Well Pit Air Temperature – 2014-10 to 2015-05-31 The February daily record shows more detail:

Well Pit – 2015-02-25 I’d say the air temperature in the pit got close to freezing, but surely a stream of cold air falling through the vent hole would wash over the logger and depress the results.
Should I get powerfully motivated, I’ll strap the logger onto one of the pipes, wrap insulation around it, and have it take data from early December through late March in one session; lifting the concrete slab requires enough effort that I’m not going to do it, ah, lightly during the snow season.