Why will water evaporate more slowly on humid days?

On humid days when the air is already saturated with water evaporates more slowly. I hope this helps

On dry days, sweat evaporates quickly, which means it also carries away heat faster. On humid days, when the air is already saturated with water, sweat evaporates more slowly. This explains why it feels so much hotter in high humidity.

Humid continental climate is found in the interior of continents between the 30 and 60 degrees latitude, but usually above the 40 degree line.   40 degrees north of the equator means less direct sunlight and therefore less warmth.   this climate is mainly found in the northern hemisphere since there are no major landmasses in the southern hemisphere.  if you live in northern indiana, you know all about humid continental because that is the climate type you have!