03/20/2025
VERY IMPORTANT reminder as we head into traditional peak tornado season in most of the United States! There are different levels of Tornado warnings and different criteria for labelling a warning.
These are impact-based warnings, and here are the specifics. Some of these specifics are mainly for meteorologists, however you might want to acquaint yourself with them too!
Most commonly, you'll see four types of warnings:
1.) A basic Tornado Warning, with a “radar-indicated” tag. Can also include a “Considerable” tag. This is the lowest threshold for warning issuance, not requiring confirmation on the ground or debris signatures on radar. Sometimes there are radar coverage gaps, visibility gaps, or other issues that make confirmation hard to impossible.
2.) A Tornado Warning, confirmed or reported. This would either have been observed by sources and corroborate radar, or confirmed on radar via a TDS. A “TDS” or (tornado debris signature) is a common confirmation tool, where we can use correlation coefficient, a tool to detect different debris or hydrometeors aloft. This could also contain a “considerable” tag.
3.) A PDS Tornado Warning (particularly dangerous situation). This would likely contain the “considerable” tag or “catastrophic” tag and have at least the 50kt-70kt *Vrot* as seen below. This is one step below an “emergency”. This would likely have confirmation from ground truth, and a very distinct signature on reflectivity, velocity, storm-relative velocity, and correlation coefficient. A TDS would probably be very distinct on radar, and the tornado could be capable of intense damage, for a PDS warning to be issued.
4.) A Tornado Emergency. This is the highest tier of tornado warnings that can be issued. This is reserved for dangerous tornadoes in a threatening location, and contains the “catastrophic” tag. A TDS must be present on radar or confirmed, and 70kt *Vrot*, STP>6. Several historic tornadoes in populated areas have been issued as "emergencies", and these are reserved for only the most dangerous of events.
*Vrot = mesocyclonic rotational velocity. In simple terms, this is how we measure the strength of the rotation inside of a supercell or the central updraft structure of a particular cell. This helps us determine if tornadogenesis is likely, and if an intense tornado may already be ongoing.
