What Is A “Particularly Dangerous Situation” Tornado Watch?
A tornado watch is a severe weather-related advisory issued by the Storm Prediction Center (an arm of the National Weather Service) whenever weather conditions are favorable for the development of tornadoes, as well as a type of severe thunderstorm(s) called a “Supercell,” that are capable of producing tornadoes (for this reason, a tornado watch also implies that a thunderstorm watch is also in effect).
A tornado watch does not mean that the severe weather is actually occurring, only that the proper atmospheric conditions exist to create a significant risk for severe weather that includes tornadoes. However, during times anticipated intense atmospheric instability, the Storm Prediction Center (SPC) will issue what’s known as a particularly dangerous situation (PDS). A PDS is a type of enhanced severe weather advisory indicating a very high likelihood of strong, long-lived tornadoes capable of creating a high risk of intensely severe and life-threatening weather.
PDS tornado-related watches are quite uncommon, which speaks to their urgency insomuch as weather advisories. In fact, less than 3% of watches issued by the SPC from 1996 to 2005 were PDS watches (or an average of 24 each year). Whenever a PDS watch is issued, there are typically more PDS watches issued for the same weather system covered by the first watch. For this reason, PDS tornado watches are associated with anticipated major tornado outbreaks (that contributes to the fact that the issuance of PDS tornado watches are quite low).
PDS tornado watches are issued when there is a higher than normal level of confidence for the formation of multiple strong to violent tornadoes (F2-F3 on the Fujita Scale) or violent tornadoes (F4-F5 on the Fujita Scale) will occur in the watch area. In addition, PDS tornado watches also indicate an increased threat for significant wind and hail damage from severe and supercell thunderstorms.
In the overwhelming majority of the cases, PDS tornado watches are often issued during the height of what’s known in meteorological terms as tornado season (the period between late March through mid- to late June each year, when the majority of the most violent tornadoes are likely to occur in the U.S.). For this reason, people living in tornado-prone regions, particularly the region known as “tornado alley” should be extra vigilant during the height of severe weather season for particularly strong tornadoes that threaten life and limb (See: Are You Ready For Tornado Season?)
Whenever a PDS tornado watch is issued, those residing in the watch area should review plans for tornado safety. This includes checking emergency supplies, and ensuring access to designated tornado shelters. Those living in sturdy-built homes with basements and/or storm shelters should be prepared to move to those shelter areas should a tornado warning be issued (See: The Most Commonly-Issued Weather Watches & Warnings - A Glossary).
For those living in homes without such shelters, ensure that there is an equally (or marginally-less effective) shelter to take cover in the event of a tornado in the form on an interior room without windows, with as many walls between said room and the outside as possible; interior closets or bathrooms without windows are best. If an interior bathroom is to be used as a shelter, crouching in a tub and covering the body (ies) with a mattress will provide the best protection against flying debris.
Those living in mobile or modular homes, or trailer parks need to know that such dwellings provide absolutely no real protection against strong tornadoes (as well as high winds created by strong thunderstorms). Even mobile homes equipped with tie-down systems cannot withstand the force of a tornado's winds. For this reason, these places need to be abandoned during a tornado warning. Make plans to leave mobile homes and seek shelter as quickly as possible during a tornado watch, preferably in a nearby building with a basement, or a neighbor’s home (it is a good idea to make agreements with neighbors, ahead of time, to share use of their home/shelter in the event of a tornado warning). Some areas have buildings designated as public tornado shelters that are opened to the public during the threat of severe weather. It’s a good idea during a PDS tornado watch to move to such facilities, just to be safe.
Finally, if no shelter is immediately available, leave vulnerable dwellings and seek shelter in a drainage ditch, or a similarly low indentation at ground level. Then cover the head with both arms and hands. The goal is to get as low as possible, so as to avoid being struck with flying debris—the number one cause of injuries and deaths in tornadoes.
Fortunately, our understanding of meteorology and the weather has improved over the decades so as to increase our ability to warn the public of impending severe weather. And during a particularly dangerous situation tornado watch, the urgency of this type of weather advisory—ironically—creates added level of warning to those who might be affected by dangerous weather. Whenever the Storm Prediction Center issues a PDS tornado watch, the level of vigilance for those who might be affected should be increased to match the increased level of threatening weather.
- The No-Nonsense Guide To Tornado Safety (Enhanced Edition) by Jeffery Sims, Paperback | Barnes &
Publications like the "No-Nonsense Guide To Tornado Safety (Enhanced Edition)" contains a list of public tornado shelters for those living in tornado-prone regions.
"The No-Nonsense Guide To Tornado Safety" contains a great deal of life-saving information related to tornado safety, including an appendix listing several pages of public tornado shelters.