reficius1

reficius1 OP t1_ivhbkso wrote

This is [OC], plotted in MS Excel. Data source:

https://www.extremeweatherwatch.com/cities/concord#:~:text=The%20highest%20temperature%20ever%20recorded,occurred%20on%20July%203%2C%201966.&text=The%20lowest%20temperature%20ever%20recorded,occurred%20on%20February%2016%2C%201943

Method was simply to scroll through the yearly data and note dates of first and last temperature of 32F/0C or lower. Probably could have automated it, but that would have taken at least as long as this did.

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reficius1 OP t1_itgps3o wrote

I'm gonna guess it was some kind of fog. Strange how it came and went in place, without rolling in from some particular direction. We were out later watching stars, and there was definitely a very thin cloud cover of some sort.

1