Supercells, hail, damaging winds, and severe thunderstorm warnings
This severe thunderstorm monitor tracks active severe weather worldwide, including supercell thunderstorms, large hail, damaging straight-line winds, and tornadoes. Users searching for severe weather near me, severe thunderstorm warning, or storm tracker can see active warnings, watches, and storm cell positions in real time.
A thunderstorm becomes severe by US National Weather Service criteria when it produces hail at least 2.5 cm in diameter, wind gusts of at least 93 km/h, or a tornado. Most thunderstorms — even those producing lightning and heavy rain — never reach severe status. Three storm modes produce most severe weather: supercells (rotating, long-lived), squall lines (organised in long lines), and multicell clusters (groups of cells in various stages of life cycle).
Supercell thunderstorms contain a persistent rotating updraft called a mesocyclone. Vertical wind shear — wind changing speed and direction with height — tilts updrafts and separates them from the rain-cooled downdraft, allowing the storm to live for hours and produce the most violent tornadoes, largest hail, and most extreme winds. Classic supercells are responsible for the vast majority of significant tornado outbreaks and softball-size hail reports.
Severe convective wind events range from microbursts — localized downbursts under 4 km wide producing very intense damage — to derechos, long-lived wind storms covering hundreds of kilometres. Derecho criteria require wind damage swaths of at least 400 km with gusts above 93 km/h. The June 2012 derecho across the eastern US and the August 2020 Iowa derecho both caused billions in damage and prolonged power outages.
When a severe thunderstorm warning is issued, move to the lowest floor of a sturdy building, away from windows. Tornado warnings require an interior room or basement. Avoid sheltering under trees outdoors, in open vehicles, or under highway overpasses. Severe thunderstorm watches mean conditions favor development; severe thunderstorm warnings mean a severe storm is occurring or imminent in your area.
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