Your fancy mountaineering watch fixes your elevation and predicts the weather by measuring barometric pressure, or the weight of the column of air above you. The higher you go, the less air there is, the lower the pressure. Likewise, an approaching storm can cause barometric pressure to free-fall hours before any clouds show up. When pressure drops for an extended period and elevation isn't the cause, a watch's storm alarm beeps, or an image of menacing clouds appears. Suunto's new watches give a warning when pressure declines continuously for three hours. But always double-check any storm alarms by scanning the sky. If pressure drops are accompanied by southerly winds, warmer air, and heavier cloud cover, expect rain within 12 hours. If those atmospheric clues aren't evident, your watch's pressure sensor could be acting up. Recalibrate it by inputting the known elevation of a city, airport, or trailhead at your current location.
Filed To: Science