Under the Weather


DO YOU HAVE the impression, as I have, that the advent of the “feelgood” evening news program — now standard fare on local TV stations across the country—has coincided somehow with the emergence of a “feelbad” school of weather reporting?

It used to be, if memory serves, that weathermen looked for the silver lining in every cloud. When the weather was wet, they would say things like “Well, we needed the rain” or “Good weather for ducks, anyway.” When the weather was hot, they would say, “Come January, you’ll be wishing for a day like today.” When the weather was bitterly cold, they would say, “A nice night to curl up in front of the fire with that book you’ve been putting aside.” Weathermen were far from adept at forecasting, but at least they attempted to ease one into the elements.

Somewhere along the way, even as rain was turning into precipitation, TV weathermen metamorphosed into meteorologists. They obtained graduate degrees and the imprimatur of the American Meteorological Society. At the same time, they acquired powerful new tools for the precise calibration of human misery. With these it became possible to contemplate the weather and pronounce that conditions once tolerated as merely bad were in fact worse than anyone had imagined.

The innocent beginning of this trend was an innovation conceived in 1939 bv Paul Siple, an American geographer and explorer. Accompanying Admiral Richard E. Byrd on his Antarctic expeditions, Siple had become concerned with the combined effect of high winds and low temperatures on the human body. His efforts to gauge the aggregate “cooling power" of low temperature and moving air led to a doctoral dissertation and to the first formulation of the concept of windchill. Siple’s windchill factor has been employed by the military since the Second World War. It was widely adopted by civilian forecasters during the nationwide overhaul of local TV news broadcasts which occurred in the 1970s.

The basic windchill formula—of which several variants now exist—yields a numerical scale for the rate of heat loss from the human surface. The scale can be translated into equivalencies of sensation, or “apparent temperatures.” Windchill tables reveal, for example, that an ambient air temperature of 25° Fahrenheit in conjunction with a twenty-five-mile-an-hour wind has the same effect on naked flesh that a temperature of — 13° would have on a windless day. In places like Iowa and Minnesota the windchill factor can produce apparent temperatures of —60° or —80°. Even in moderate climes windchill frequently pushes the perception of cold below the zero mark. The thermometer may well say 35°, meteorologists warn, but exposed human tissue could still suffer cryogenic trauma.

The warm-weather analogue to windchill is variously called apparent heat, humature, the heat index, or the temperature-humidity index. The concept of apparent heat was introduced by Robert Steadman, a textile-research engineer now teaching at Texas Tech, in Lubbock. Steadman’s pioneering work “The Assessment of Sultriness” appeared in the Journal of Applied Meteorology in 1979; broadcasters quickly incorporated his temperature-humidity index into their weather reports. Apparent heat, Steadman wrote, “is the temperature which a given combination of drvbull) temperature and vapor pressure ‘feels like’ to the typical human.”Various tables have been compiled, similar to those for windchill, correlating likely combinations of temperature and humidity with equivalent values of apparent heat. If the dry-bulb (actual) temperature is 95°, say, and the relative humidity is 50 percent, then the apparent heat is 105° and falls within what the National Weather Service calls the Category II range—“sunstroke, heat cramps, or heat exhaustion likely, and heatstroke possible with prolonged exposure and/or physical activity.” Standing in the shade does not help. Apparent-heat tables assume that one is there to begin with—and wearing a short-sleeved shirt. Needless to say, meteorologists are fond of apparent heat.

They are fond, too, of the air-quality index and the pollen count. And in those parts of the country that possess what Washington terms water-sensitive economies, meteorologists are prone to cite the Palmer drought index, the cropmoisture index, and the monthly-moisture-anomaly index. Not long ago, as autumn segued into winter, I was introduced to the dispiriting notion of heating-degree-day units, or HDDUs. Heating-degree-day units represent the number of degrees by which the average temperature in a given day falls short of 65° F. It turns out that in Massachusetts, where I live, the average daily HDDU deficit during the coldest half of the year is about 30 degrees. (The cumulative deficit, from the end of summer to the beginning of spring, runs to more than 5,000 degrees, an amount that, if subtracted from the total number of degrees logged in July and August, would produce two solid months of subzero weather.) For those who elect to remain indoors during prolonged cold spells, some forecasters now provide a potential-indoor-relative-humidity index. This measure can be used to predict whether static electricity (fostered by central heating, which dries the air) is likely to be a minor annoyance or a pitiless scourge.

The newest family of forecasting indexes may transform meteorology into a sterner science still. Working on the assumption that atmospheric conditions have predictable and quantifiable effects on emotion, behavior, and physical wellbeing, a Minneapolis-based company called MultiData issues “bioweather” indexes for a hundred regions nationwide. Atlanta’s twenty-four-hour Weather Channel, which has 1,700 cable affiliates and is received in 19 million homes, employs two of MultiData’s diagnostic tools: the aches-and-pains index and the respiratory index. The Weather Channel has not yet subscribed to the moods index, the reflex index, or the thinkingproficiency index, but television stations in Cleveland, Wilkes-Barre, Baltimore, and Washington, D.C., now offer one or more of these. Before long it may be possible to learn from one’s meteorologist that the morrow will bring not only snow and sleet but also a 50 percent chance of neuralgia, scattered neuroses, and a possibility of late-afternoon nescience, with a likelihood of electrostatic squalls from the radiators in outlying suburbs.

You don’t have to be a weatherman to know which way the wind is blowing: new indexes, ever more refined, doubtless lie ahead. Few facets of human experience will remain untouched. Shall I part my hair behind? Do I dare to eat a peach? Weather forecasters may one day venture prescriptions on matters such as these. Perhaps by then the rest of us will have learned that the only advisory truly worth heeding is the forecast issued centuries ago by Jonathan Swift: “’Tis very warm weather when one’s in bed.”

—Cullen Murphy