Heat waves are a part of summer months
On Aug. 7, 1918, Philadelphia hit its hottest temperature ever — 106°F. While it won’t get that hot today, it may feel even hotter.
Temperatures have stretched high up near the 100°F on multiple occasions this summer. Following suit, this week is bringing with it another brutal heat wave. But what do heat waves really mean, and what effect can they have on people?
In general, a heat wave is defined as a period of three or more days that consists of temperatures notably above the average for that time period. For our area in mid-August, three consecutive days at 90°F or above would be considered a heat wave.
Heat waves are caused by high-pressure systems, especially when they sit over an area for a prolonged period. This is because highpressure systems force air downward. As a result, the air near the surface is unable to rise. Without any air rising, there is little circulation and nothing stopping the trapped surface air from getting hotter.
A recent time when an extreme heat wave hit was in the Pacific northwest between June 26 and June 28. A perfect example is Seattle, which surpassed 100°F three days in a row, the first time in its history that has been done. In the process, Seattle reached a whopping 108°F, shattering the all-time record of 104°F — from the day before — and 103°F from 2009.
Despite these tremendous temperatures, Seattle was spared one factor that is commonly seen around here: humidity. This is a factor that creates the sticky, heavy, and at times unbearable environment in our area.
Normally, it is measured as relative humidity, which is a percent based on the amount of water vapor in the air. The higher the percentage, the more humid it is, and the wetter it feels.
The maximum amount of water vapor that the air can hold is represented by the dew point. This is measured as a temperature, and the higher it is, the more humid the air feels. Also, the closer the dew point and the temperature are to each other, the higher the relative humidity is. This may seem confusing, but the three terms are interconnected. Think of the dew point being the numerator, the air temperature being the denominator, and the relative humidity being the percentage that it creates.
So, why is humidity so bad? Humidity makes the body’s method of cooling down — sweating — less effective. The body cannot release more water into an environment that already has a lot of water in the air. In short, it makes the air feel hotter. Sometimes, a lot hotter.
Humidity and heat combine to form the “feels like” temperature, or the Heat Index. It factors in the humidity and the actual air temperature to see what it really feels like outside.
For example, on July 13, Death Valley, California had an air temperature of 108°F. With a low dew point of 56°F, and subsequently a low relative humidity of 18%, it felt very similar to the actual temperature with a Heat Index of 111°F.
But on July 8, 2003, when Dhahran, Saudi Arabia had a temperature of 108°F, it had a worldwide record-high dew point temperature of 95°F, with a relative humidity of 68%. This created a Heat Index of 178°F. Man, that’s hot.
While maybe not to that extreme, the Philadelphia region is well versed with humid heat. Today, with a dew point in the mid70s and temperatures in the mid-90s, it will feel up to 110°F outside. In fact, we’ve had at least 11 days that felt over 100°F so far. So, with such extreme weather, how could one go about their daily lives without any A/C? That is the question that many had to deal with before A/C existed.
“We used a window fan that my dad brought from work in the evenings to pull the hot air out of the house; (it) made all the difference on those hot nights,” says Edith, a longtime Pottstown resident. This was a smart strategy, as fans can be used to push or pull air from a certain location depending on which way then spin. For others, water was the answer.
“My grandmother had a galvanized zinc tub she used for the laundry that we would fill with cold water from the tap and put it in the yard, in the shade, and jump in to cool off. It would only fit two of us kids at a time, it was so small, but it was as good as having a pool to us kids back then!” recalls Bessi.
But for everyone, it was just a known price to pay.
“People just didn’t complain about the heat back then. It was summertime so we knew it was going to be hot and we just went about our business,” says Eunice.
While it’s safe to say that this summer has been a hot one so far, we should consider ourselves lucky to live in an age where we have more weapons to fight the heat than ever before. Stay cool out there.
Will Cano is a junior at Owen J. Roberts High School who has a passion for the weather. You can find him on any given day reciting weather forecasts and events to his peers. Will founded the Meteorology Club at his high school and is currently the president. He also won awards in the middle school science fair from both NASA and the American Meteorological Society with his project on atmospheric aerosols and hurricanes.