Around 4.30pm, a severe thunderstorm warning was issued for Mandurah and surrounding areas.

The severe thunderstorm warning was immediately upgraded to a tornado warning.

On the evening of July 1, 2010, Yorkton received a severe thunderstorm warning.

These are issued as special weather statements written in the style of severe thunderstorm warnings, rather than being an official product itself.

A severe thunderstorm warning means there is significant danger for the warned area.

Another computer mistake later today sent an erroneous thunderstorm warning for parts of Illinois.

This alert product was created in the early 2000s, and is sometimes a precursor to a severe thunderstorm warning.

Although a severe thunderstorm warning was issued at 2:57 pm, very few people received the warnings in time.

Severe thunderstorm warnings, by their nature, will be issued less than one hour in advance.

A severe thunderstorm warning can be upgraded suddenly to a tornado warning should conditions warrant.