People who try to guess what temperatures should have been in the past are not thinking clearly. A change in elevation can cause temperatures to either increase or decrease. Along the Colorado Front Range, temperatures in the foothills are almost always higher than they are down at lower elevations. Cold air sinks.
As far as TOBS goes, you have no idea if a station operator in 1940 reset their thermometer before they went to bed, as anyone would do who wanted to get meaningful data would do. You don’t know when the road got paved in front of their house. You don’t know when the city started doing snow removal. You don’t know when they planted a lawn, painted their house a different color or installed an air conditioner. There are dozens of factors which affect temperature which can’t be guessed about the past.
Leave the data alone. Adjusting the data…
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