Camping Special, April 1997
Temperature. Rapidly falling mercury levels portend stormy conditions, so keep aware. If you don't have a thermometer, try counting the chirps a cricket makes in one minute, subtract 40, divide by four, and then add 50--that's the approximate temp. Two other handy indicators: Dandelions close up below 51 degrees, and your breath becomes visible at 45.
Wind. You can estimate a breeze's speed and direction by watching which way and how forcefully it blows the surrounding branches, leaves, and grass; know, too, that clover shuts when gusts exceed 20 miles an hour. Pay particular attention to sudden, counterclockwise shifts in wind direction, especially those that move from north to south, which often mean an approaching storm.
Humidity. Perhaps the most accurate harbinger of a really nasty thundershower, humidity is none too hard to determine when humping your pack--your rate of perspiration speaks volumes. But it's less easy to estimate when you've stopped for a break near a stream or to take a dip in a mountain lake. For such times, keep in mind that frogs croak more frequently in muggy weather--the increased humidity enables them to stay out of the water longer--and the scarlet pimpernel, long dubbed "the poor man's weather glass," folds its petals when humidity levels exceed 80 percent.
Pressure. Low barometric readings tend to indicate imminent rain. So look for bubbles forming around the rim of your coffee cup and campfire smoke hovering close to the ground--both occur when the barometer is falling.
Finally, if you want to approach do-it-yourself forecasting a bit more seriously, consider carrying a two-part "weather kit," consisting of a Casio Pathfinder Triple Sensor wristwatch ($170; 800-962-2746), which displays temperature, altitude, and barometric pressure; and a chart to help you interpret the raw data. You can find the latter by pointing your Web browser to www.usatoday.com/weather/wfbarrow.htm.
Illustration by Ross MacDonald