Barometer Rule for Severe Storms
An ordinary thunderstorm requires:
  • barometric pressure of less than 1009 mb; and
  • last 3 hours pressure fall of 4 mb or more.
A severe thunderstorm produces one or more of the following:
  • wind gusts of 90 km/h (56 mph) or greater; or
  • hail of 2 cm (3/4 inch) diameter or greater; or
  • flash floods;
  • or tornadoes.
A severe thunderstorm requires:
  • barometric pressure of 1005 mb or less; and
  • last 3 hours pressure fall of 4 mb or more; and
  • last 12 hours pressure fall of 8 mb or more.
Even though the pressure fall can be spread over 12 hours, a severe thunderstorm will still have a 3-hour interval where there will be at least a 4 mb fall in pressure.

Applying the Secret Law of Storms gives asustainable wind speed for a severe storm of 56 km/h (or 35 mph). Severe thunderstorms often generate strong wind gusts when rain and hail drag down the surrounding air. Evaporation further cools it accelerating the downdraft. Gusts of at least 90 km/h (56 mph) are produced.Asevere thunderstorm gives a rainfall rate greater than 50 mm (2 inches) in one hour.

Tropical Revolving Storms are referred to as cyclones in the Indian Ocean and South Pacific, typhoons in the Western Pacific and hurricanes in the Western Atlantic and Eastern Pacific Oceans. A Tropical Revolving Storm satisfies the Barometer Rule for a Severe Thunderstorm and so does a Tropical Storm.
My Barometer Rules
Last 3 hours
▲10 mb Gale Warning (34 – 47 knots)
▲6 mb Strong Wind Warning (26 – 33)
▼4 mb storm ( < 1009 mb)
▼6 mb storm with a Strong Wind Warning ( <1009 mb)
▼10 mb storm with a Gale Warning( < 1009 mb)
Severe Thunderstorm Warning
Last 3 hours ▼4 mb Last 12 hours ▼8 mb
(Pressure < 1005 mb)
Source: Secret Law of Storms
Thunder & Bushfire Storms app: