Tornadocane

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Tornadocane is a portmanteau of the words "tornado" and "hurricane" given to certain Mesoscale Convective Systems that develop a weather radar signature in the shape of a hurricane in low levels. These storms have a central eye free of precipitations with surrounding arms of strong echoes but are really associated with a supercell thunderstorm developing a squall line. These storms are not in any way related to a hurricane other than the fact that they are shaped similarly to one. A good example of a tornadocane occurred on April 15, 1999 over Duplin County, North Carolina^[1] .

1 Formation
2 North Carolina case
3 Other case
4 See also
5 References
6 External links

[edit] Formation

These unusual thunderstorms complexes begin as the rear flank downdraft of a supercell thunderstorm generates a vigorous gust front at the base of the hook echo region. If the instability and humidity of the air ahead of the front are right, a squall line develop from the supercell toward the southwest (northern hemisphere) closing the gap of the bounded weak echo region (BWER) and curving into spiral bands seemingly rotating around the BWER. The supercell itself is often associated with tornadoes while the squall line produces microbursts.

[edit] North Carolina case

This tornadocane began as an HP (Heavy Precipitation) supercell on April 15, 1999, and moved across North Carolina while assuming a hurricane shape. It exited the State as a Bow Echo as the parent supercell decayed and the squall line took over. One tornado spawned from this supercell was .8-1.6 km (.5-1 mi) wide, caused major damage and injured 11 people along a 48 km (30 mi) long damage track^[1].

One death and a 265 km/h (165 mph) wind gust were also reported with this storm. This wind gust is thought to have come from a direct hit to an anemometer by a tornado, making it an EF3. Since only damage can be used to infer the strength of a tornado, that recorded wind speed is ineligible for determining the EF scale rating of this tornado^[1].

The Tornadocane reflectivities from a Weather radar display.

Filtered image of the Tornadocane with all dBZ Reflectivities less than 35 taken out.

Storm Relative Velocities showing rotation in the storm (red-green doublet).

[edit] Other case

Tropical cyclone-like vortex over Pennsylvania on July 21, 2003

Another case of tornadocane happened across the Midwest on July 21, 2003. An area of convection developed across eastern Iowa near a weak stationary/warm front at 0302 UTC and moved to the east along it. By 1203 UTC, the convective system had matured, taking on the shape of a wavy squall line across western Ohio and southern Indiana. The system re-intensified after leaving the Ohio Valley, starting to form a large hook, with occasional hook echoes appearing along its eastern side. A surface low pressure became defined and became more impressive later in the day. By 2244 UTC, a squall line took shape along its band to the south. This began to starve the inner convection and by 0126 UTC, daytime heating had ceased. The squall line ran out ahead of the low, causing the entire convective structure to weaken.^[2]

Heavy rainfall and straight wind damages were the main effect of this system. It left a maximum of 102 mm (4 inches) of rain along the path of the system and numerous reports of violent winds. A few weak tornadoes have been reported too.