National Weather Service Tornado Warning Policy: Is It Time to Account for Weak and Short-Lived EF-0 Tornadoes?

Tornado Warnings (TORs) are issued by the National Weather Service (NWS) to protect lives and property. NWS forecasters issue TORs to provide the public and emergency managers with advance notice of tornadoes, and are issued when there is radar indication and/or reliable reports of a tornado or developing tornado.

Over the past decade, many weak EF-0 tornadoes have occurred in the Baltimore/Washington Weather Forecast Office’s area of responsibility. Most of these weak tornadoes are on the ground for at most a few minutes, and produce very limited damage (e.g., a few trees down), that is confined to a very small area. In the current NWS warning paradigm, a TOR would be issued whether the tornado was a weak EF-0 tornado, or a catastrophic EF-5 tornado. While the text of the warning may be different between these two extremes, the same communications systems would be activated. Moreover, with the advent of the FCC’s Wireless Emergency Alerts, many more people are being alerted to all ranges of tornadoes, including the weak EF-0 tornadoes. This increases the risk of “crying wolf” syndrome, where people start ignoring Tornado Warnings, because they haven't experienced any impacts despite being in a TOR. This syndrome has been well-documented in recent NWS National Service Assessments.

With the advent of increased resolution of the WSR-88D Doppler Weather Radar through hardware and software upgrades, over two decades of corporate experience using the WSR-88D, and with supplemental weather radar coverage in some locations by the FAA’s Terminal Doppler Weather Radar, it is hypothesized that there can be skill at times in determining weak and short-lived EF-0 magnitude tornadoes from those that of a higher magnitude, stay on the ground longer, and thus more likely to have a greater impact.

This presentation will compare and contrast radar imagery of EF-0 tornadoes vs. imagery of stronger tornadoes, and show as a basis of discussion that there is skill at being able to identify weak, EF-0 tornadoes vs. stronger tornadoes that have much more impact. If the discussion basis is accepted, then it is suggested that the NWS adjust its Tornado Warning policy to somehow account for weak, EF-0 tornadoes. This would provide more effective communication techniques in response to NWS TORs, resulting in the public making changes in their response behavior, thus better decisions.