The hidden reason this Rochester heat wave feels so intense

ROCHESTER, N.Y. (WROC) — Air temperatures during this week’s heat wave are forecasted to reach the mid-90s at their peak. These temperatures aren’t completely unheard of in Rochester; they’ll be in top rankings for their respective days’ historical highest temperatures, but probably won’t be topping those lists. But the air temperature isn’t the primary concern. It’s the dewpoint temperature. Think about the human body for a second. When we start getting hot, our bodies produce sweat. The sweat evaporates into the air around us, eventually cooling us down. This is a process known as evaporative cooling. Now back to dewpoints. The dewpoint is the temperature air has to reach in order to become fully saturated. So, the more water in the air, the higher the dewpoint. When there’s less water in the air (lower dewpoints), there’s enough room in the air around us for our sweat to evaporate. But when there’s already a lot of water in the air (higher dewpoints), there’s not as much room in the air for our sweat to evaporate, so evaporative cooling can’t happen as effectively. This is why we calculate a heat index. It factors dewpoints in with the air temperatures to give humans an idea of what it will feel like to us outside. It may surprise you that the heat index equation actually only calculates what it would feel like in shady spots. Direct sun exposure can feel even hotter than the “feels like” temperature. Data on dewpoints is hard to collect, but we do know that the average dewpoint temperature in Rochester in July is about 60 degrees. Some National Weather Service offices in more moist climates stay on top of their dewpoint data, like NWS Tampa. If you’ve ever been in coastal Florida, you know how stifling that air feels. Their average dewpoint temperature in July runs around 73-75 degrees. Our dewpoints during this heat wave will be in the mid to upper 70s. A little higher than typical summertime in Tampa, but a lot higher than typical summertime in Rochester.