Tuning into the Weather Channel last evening, I watched their coverage of thunderstorms with intense lightning crossing southeastern Wisconsin, where the ground temperature was only in the low 40s F. Since we generally associate thunderstorm development with warm, humid weather, this scenario might seem confusing.
Since warm air rises and cold air sinks, most thunderstorms develop when warm, humid air at the surface rises into colder air aloft; this convection is often facilitated by an approaching cold front that augments the lift. Thunderstorms that develop in cold weather can be attributed to one of two conditions: when even colder air sits above the surface air (often producing thunder and lightning during snowstorms) or when warmer air overrides cold air at the surface. In the latter circumstance, the thunderstorms are said to be "elevated" since the convection develops as the warm middle layer interacts with cold air above it. Rain that is produced by these elevated storms is often mixed with hail (as occurred last evening).
While the most powerful thunderstorms, sometimes producing tornados, usually develop on hot, humid days, cold thunderstorms can also produce damage as strong, cold downdrafts develop within the storms. Watch for these elevated thunderstorms when warm fronts push northward into colder air at the surface.
