The chart is a grid where you can find the heat index temperature by looking at the air temperature and relative humidity. For example, the NWS says if it's 96 outside and the humidity is 65% ...

PITTSBURGH (KDKA) — Oftentimes in weathercasts, you'll hear KDKA-TV's First Alert meteorologists mention the relative humidity and dew point, but what are these two terms and what do they mean?

The optimal relative humidity for indoor air is between 30 and 50 percent, far above the 10 percent it can drop to in winter. The right humidity benefits you in myriad ways. It can also be helpful ...