Severe Storm Definitions & Whirlwind Classification Scheme


Severe thunderstorm & severe local storm

At the fifth TORRO conference, held jointly with the Royal Meteorological Society at Imperial College, London, in October 1994, David Reynolds presented TORRO's definition of a severe thunderstorm and severe local storm.

TORRO defines a severe thunderstorm as a thunderstorm which has:

As these elements may also occur without thunder (although in reality, a H3 hailstorm is highly unlikely to be thunderless) so a wider definiton of a severe local storm can then be made. Thus, TORRO defines a severe local storm as:

The additional statement at the end of (iii) is required in order to exclude the widespread high winds brought by deep depressions.


Whirlwind classification scheme

Dr. Terence Meaden devised TORRO's whirlwind classification scheme, which is outlined below.

Vortex, whirlpool and whirlwind
As a preamble, a vortex may be defined as a rotation within a fluid. If the fluid is a liquid, the vortex may be more accurately termed as a whirlpool, while if it is a gas it is termed a whirlwind.

Major, minor and other whirlwinds
TORRO then sub-divides a whirlwind into major, minor and other whirlwinds.


Abbreviations

The following abbreviations are regularly used by TORRO, especially in reports and databases:

BL - ball lightning
EF - St. Elmo's Fire
EW - eddy whirlwind
FC - funnel cloud
FD - fire devil
HS - hailstorm
LD - land devil
RS - remarkable shower
TN - tornado
WD - water devil
WS - waterspout
WW - whirlwind

An abbreviation in upper-case indicates certainty in the report, while the use of lower-case indicates events where a small degree of uncertainty exists about the true cause. For example, TN indicates a definite tornado, while tn indicates a probable tornado.

However, in all instances the Beaufort letters q (for squall) and kq (for line squall) remain lower case regardless of their certainty.

It should be pointed out that ball lightning is not accepted by some scientists, while others are uncertain of its existence. From that stand-point, the use of the abbreviations BL and bl in this context would not be acceptible. It is the opinion of TORRO, as well as of many other scientists, that - in the balance of probability - ball lightning does exist as a real phenomena, whose nature is currently uncertain.


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