A large shelf cloud was spotted amid lightning flashes over the city of Fort Myers on Monday night as strong storms moved over Lee and Collier Counties.
Shelf clouds are not uncommon during stormy weather, and they are one of nature's most ominous cloud formations, especially when viewed from a distance.
Developing on the leading edge of a strong or severe thunderstorm, shelf clouds develop as blocky, C-shaped features visible in the right conditions far away from where a storm is moving. The thick shelf-looking feature these clouds are known for is generated because of the interaction of a storm's downdraft and updraft.
When thunderstorms form, they push cool, dense air downward toward the Earth's surface forming what are referred to as a thunderstorm's downdraft. When this air reaches the Earth, it can't break the surface. Instead, it pools out along the ground in front of the storm. This creates what's known as a gust front or outflow boundary.
The air around storms is often warmer and more unstable than the air being pushed down from a storm in its downdraft. Since warm air is less dense than cool air, gust fronts racing out ahead of thunderstorms force relatively warmer and less dense air upward. This air cools forcing it to condense into water droplets making clouds. This is why shelf clouds have such a stiff-looking face; the proximity of cool air sinking and warm air rising rapidly ahead of it.
Though shelf clouds can accompany severe weather, they're not tell-tale signs of severe wind or tornadoes. Shelf clouds are often misidentified as twisters or wall clouds based on how they appear when viewed from the ground.
The storms that produced tonight's shelf cloud will continue moving westward toward the Gulf of Mexico. Another round of rain and storms will be possible on Tuesday afternoon and evening.