If you are interested in looking at long-term trends in climate across the US, this “Beyond the Data” article by Jake Crouch does a great job of explaining where to get trend data and how to interpret it.  I use NCEI’s tooks like the “Climate at a Glance” tool all the time when I give talks about how climate varies across Georgia and the Southeast.  You can find the blog article at https://www.climate.gov/news-features/blogs/beyond-data/mapping-us-climate-trends.