When I took a closer look at this USA temperature map, it appears to be heat transfer. In other words, when the cold air descended from Canada it cooled the hot air mass over the country.

Depending on the heat of the air; the colder air would cool that air unevenly. A city is hotter than a grassy field. The same cold air would pass over both and cause a different fall in temperature. It would not be uniform throughout.

I hadn't watched the Canadian air mass closely, but, since the hurricane wouldn't let it into the southeast it went into Mexico.

That is the way I see it at this point. There have been hurricanes into the Eastern Pacific that could also be cooling Mexico as well.