That's actually a pretty good arrangement. It allows one to see patterns.... for example, late December appears to have a consistent set of very cold days, clustered right around Christmas.
I don't see any unusual changes to the distribution. What years does this cover?
I also notice a couple of bands of missing data?
It seems to me that noticeable changes in weather, ie, earlier springs / later winter starts, are likely regional. More noticeable in places such as Ocean City, Maryland, for example. Wisconsin strikes me as being... more static? Mostly because it lies deep in the interior, more or less on the median for weather patterns, if you take my meaning.
Of course, I did just have several beers and a shot or two, so I could be wrong.....