An 'extreme heat watch' is in effect as the heat index is expected to skyrocket. Here's timing, updated heat index values, ...

Residents can use the NWS Heat Index Calculator to calculate what the heat index is locally. In addition, there is the Heat Index Chart with a wider range of temperatures and humidity percentages.

Residents can use the NWS Heat Index Calculator to calculate what the heat index is locally. In addition, there is the Heat Index Chart with a wider range of temperatures and humidity percentages.

National Weather Service forecasters say heat will roll in today, June 18, with Delaware and Philadelphia counties under heat advisories with heat index values, or feels-like temperatures, nearing ...

Heat index values have the potential to reach 105 degrees early next week, NWS said. Hazardous weather outlooks are issued before an advisory, watch or warning.

To determine the heat index while in a shady location, use the chart below. If you are exposed to direct sunlight, NOAA explains the heat index value can be increased by up to 15 degrees.

To determine the heat index while in a shady location, use the chart below. If you are exposed to direct sunlight, NOAA explains the heat index value can be increased by up to 15 degrees.

Basically, when the body sweats, the perspiration evaporates, cooling the body. When the humidity is high, the sweat doesn't evaporate as quickly and the body doesn't cool itself as well. Therefore, ...