Last week, Tuesday August 7th, 2012 at approximately 6 P.M. law enforcement reported a tornado over the Patuxent river prompting the National Weather Service to issue a Tornado Warning for Prince Georges, Calvert, and Saint Marys Counties. The Emergency Alert System kicked into action broadcasting the warning across television and radio. However, had you then tuned into NewsChannel 8, ABC 7 or any of the other local television stations, you would have heard that it was in fact a water spout.
So which one was it? A tornado or water spout and what is the difference?
A waterspout as defined by the National Weather Service (NWS) is a violently rotating column of air, usually a pendant to a cumulus or cumulonimbus cloud, over a body of water with its circulation reaching the water. In the summer and spring, these phenomena are usually "tornadoes over water" that have been generated by thunderstorms.
In the fall months, these most often begin as cold air funnels, being generated by a cold air mass passing over much warmer waters. Such waterspouts are generally much less intense than tornadoes and usually dissipate upon approaching shore.
A tornado meanwhile, is defined as a violently rotating column of air in contact with the ground and extending from the base of a thunderstorm. A condensation funnel does not need to reach to the ground for a tornado to be present; a debris cloud beneath a thunderstorm is all that is needed to confirm the presence of a tornado, even in the total absence of a condensation funnel.
It nearly always starts as a funnel cloud and may be accompanied by a loud roaring noise. Tornadoes are classified by the amount of damage that they cause. Again defined by the NWS.
Now making the distinction between a waterspout and tornado can get a bit confusing when a waterspout forms over water and then moves ashore or if the opposite occurs. First it’s worth noting that a waterspout forms over water due to warm temperatures in the lower atmosphere along with high humidity they are generally not as dangerous as a tornadic waterspout. These type of non tornadic waterspouts average between 3-100 meters and pack winds less than 45 knots. While rare should a waterspout move inland and somehow sustain itself then it would be classified as a tornado. This is what occurred on Aug. 7.
A tornadic waterspout on the other hand is totally different animal. For a tornadic waterspout to form you would typically start with a super cell thunderstorm, which has large scale rotation. It would originate as a tornado on land and then move onto a large body of water such as the ocean or even lakes. Tornadic waterspouts can be dangerous, destructive and deadly for those on the water or even at the Marina.
In case you are wondering the National Weather Service does not distinguish between tornadic waterspouts and non tornadic waterspouts when they issues warnings. No matter which of these you may encounter it is best be alert and prepare to seek shelter so you and your family can stay safe.
Below is "dramatic footage filmed from a helicopter by Australia's Channel 7 shows a series of powerful waterspouts near the coastal suburb of Terrigal, on Australia's New South Wales coast. Several powerful columns of swirling air could be seen blasting along the water's surface near the coastline. Channel 7 claimed the spouts reached heights of up to 600 meters (nearly two thousand feet), but dissipated as they neared land. The natural wonders came as strong winds and heavy rain also lashed other parts of the state, causing flash flooding and traffic chaos in Sydney." (Credit: RussiaToday)
Now in contrast, check out this video from Penang on November 15th 2010. (Credit: sndseen) If you watch carefully you can actually see the rotation of the entire storm.