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Weather Almanac for July 1998
It's Not Just The Heat
The air hangs heavy today. It has been one of those incredibly hot, humid days when you would love to remove your skin, but instead wander tortoise-slow around the house with the least clothing the law, or your family, will allow. Throughout most of eastern North America, the Bermuda High -- at its peak summer strength -- continues to pump tropical air from the Gulf of Mexico northward into Canada. No breeze stirs nor rain falls, although the sky is so laden with moisture that water droplets cling to the walker as if they had found a long-lost relative. The temperature is 30° C (87° F) and the relative humidity reads 75%. It is not yet noon.
Once established, the heat wave has intensified. The stifling flow of air from the Gulf of Mexico northward further gains heat as it passes over the hot land. All residents of the eastern half of North America languidly await the cool, dry air, so unwelcome in winter, from the Canadian North. In later afternoon, thunderstorms spawned by the heat and humidity give temporary relief, but soon afterward the added moisture drives the humidity upward, making it stickier. The high humidity also helps the air retain heat after the sun goes down, for water vapour is one of the two prime greenhouse gases, making nights unfit for sleep or even contact with the sheets.
Diane Ackerman spoke of one such day: a "brutally hot and humid summer day, one on which the sun feels as if it has been dipped in lye, the air so thick it's drinkable, and your body feels like freshly melted lead..." Or as Jane Austen remarked: "What dreadful hot weather we have! It keeps me in a continual state of inelegance."
In years past, during such weather, farm residents and workers, young and old, would gather around the rain barrel to sit and soak their feet in the cooling waters. Or jump in the pond for relief. Today we huddle close to the air conditioner and find excuses for not venturing out of doors or rely on fans and swimming pools to help alleviate the discomfort of sweltering summer heat.
The dangers posed by heat and humidity have lead to the development of various heat/humidity discomfort indices. In order to alert residents to the combined dangers of heat and humidity, Canadian and American weather services issue heat warnings similar to the windchill warnings of winter. Whereas in winter we are concerned about too rapid heat loss; in the summer, too slow a cooling rate. The Canadian index is called the Humidex; in the United States, the Heat Index. They are based on slightly different combinations of temperature and relative humidity. (For a more detailed look at heat discomfort and its indices, see Summer Discomfort in the Weather and Life section.)
Because these indices are, to some degree, subjective, the level of discomfort or danger will depend on a person's age, health and physical condition, on the type and amount of clothing worn, and their activity level. Besides the temperature and humidity, weather conditions such as amount of sunshine and wind speed also will affect the "feel" of temperature and humidity.
The sweat running down my arm dampens the paper so that the pen no longer writes smoothly. It is even too hot for thought, and so this piece is a short one.
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