What was it? A Land Spout, Water Spout, Funnel Cloud or Tornado

3 minutes reading time (608 words)

One of the reasons why the NZ Weather Enthusiasts group exists is because of the lack of clarity around weather events, often misreported in the media. This misreporting often leads to further confusion in the publics mind. As weather buffs I don't think it's a matter of being too picky. Science, and in this case Meteorology is confusing enough to the general public, without general misreporting, confusing terms and the like.

That's where a site like this one aims to help clear up some of that confusuion, and to hopefully help the general public, better understand some of the concepts and ideas around meteorology.

An interesting weather event (we'll call it that for the time being!) occurred this afternoon in the Hamilton area. If you would like a description of how this weather event occured there is a short post here. Emma Bray captured a great shot as the "event" was forming: 

WeatherWatch New Zealand called it a tornado. Metservice called it both a Tornado and a Funnel Cloud

Out of all the advice offered, Waikato Civil Defence perhaps provided the most important:

The NZ Herald clearly thought it was a tornado, and even had another forming over Tauranga. 

So what's the difference. And why are there so many names for the same "event" - surely that's confusing? Here's the official definitions from WMO for each type of event:

A severe rotating windstorm of small diameter and great destructive power. It is the most violent natural meteorological phenomenon. With certain frequency they can occur within hurricanes circulation. Although tornadoes occur over land areas in many parts of the world associated with several weather situations, they are relatively frequent in the forward portion of the hurricane periphery.

Water Spout
Small, revolving storm over oceans or inland waters. They occasionally move towards inland and cause some damage, but winds are less severe than those in tornadoes, which they resemble in appearance.

Land Spout
A tornado over land.

Funnel Cloud
Cloud formed at the core of a waterspout or tornado vortex, sometimes extending right down to the ground, caused by the reduction of pressure at the centre of the vortex.

So a land spout appears to be the same as a tornado. A tornado occurs over land, while a waterspout occurs over water. However it's not entirely clear what a funnel cloud is. Wikipedia helps define things a little better calling a funnel cloud

A funnel cloud is a funnel-shaped cloud of condensed water droplets, associated with a rotating column of wind and extending from the base of a cloud (usually a cumulonimbus or towering cumulus cloud) but not reaching the ground or a water surface. A funnel cloud is usually visible as a cone-shaped or needle like protuberance from the main cloud base. Funnel clouds form most frequently in association with supercell thunderstorms.

So it really depends on timing. It's a funnel cloud if the rotating air hasn't touched the ground, but when it does, it's a tornado.

Interestingly Wikipedia also notes the following:

In cloud nomenclature, any funnel- or inverted-funnel-shaped cloud descending from cumulus or cumulonimbus clouds is technically described as an accessory feature called tuba. The terms tuba and funnel cloud are nearly but not exactly synonymous; a wall cloud, for example, is also a form of tuba.

So now you know the difference!

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