Tornadoes are hard to predict with any certainty, and even meteorologists can only issue tornado advisories when conditions are right. Some people believe that hail, wind, or lightning will always precede a tornado, but that is not always the case, though large hailstones and other inclement weather do often occur beforehand. Another belief is that if you observe the readings on a barometer suddenly dropping, you can expect a tornado to soon form. This is not an accurate method of prediction, either. Such air pressure drops can occur hours or days before an actual tornado hits. The best strategy is to simply listen closely to weather forecasts during bad storms and trust meteorologists to issue warnings when the conditions merit caution.