A PDS tornado watch is an urgent alert issued by the National Weather Service (NWS) when conditions indicate a significantly elevated potential for severe, life-threatening tornadoes. Understanding this alert is important for public safety, prompting a higher degree of preparedness and immediate action should a tornado warning be issued.
What is a Tornado Watch?
A standard tornado watch is an alert issued by the National Weather Service’s (NWS) Storm Prediction Center (SPC) when atmospheric conditions are favorable for tornadoes to develop. These watches typically cover large geographical regions, often spanning multiple counties or states, and are usually in effect for 4 to 8 hours. Their purpose is to provide advance notice, allowing individuals to review safety plans and prepare to take shelter if threatening weather approaches.
A tornado watch differs from a tornado warning. A warning signifies a tornado has been sighted or indicated by radar, requiring immediate action to seek shelter. While a watch indicates tornadoes are possible, a warning means a tornado is occurring or is imminent. The SPC issues watches, while local NWS offices issue warnings.
The “Particularly Dangerous Situation” Designation
The “Particularly Dangerous Situation” (PDS) designation is special wording used by the National Weather Service and Storm Prediction Center to convey an extreme, life-threatening severe weather threat. This designation is reserved for rare circumstances with a high probability of multiple, long-track, violent tornadoes, typically rated EF2 or stronger, with widespread damage potential. PDS tornado watches are uncommon, making up less than 3% of all tornado watches issued between 1996 and 2005.
This designation highlights a substantially higher threat level than a regular tornado watch, signaling that an outbreak of strong or violent tornadoes poses a major threat to life and property. The SPC issues PDS watches when forecasters have high confidence that exceptionally dangerous tornadoes are likely. This wording alerts the public, emergency managers, and media to the situation’s gravity.
When a PDS Tornado Watch is Issued
A PDS tornado watch is issued when specific meteorological conditions align for severe weather. This includes extreme atmospheric instability, where warm, moist air near the surface rises rapidly, and very strong wind shear, which is the change in wind speed and direction with height. These conditions foster the development of powerful supercells, highly organized thunderstorms with a deep, persistently rotating updraft called a mesocyclone.
The decision to issue a PDS watch is based on rigorous analysis by NWS Storm Prediction Center forecasters, who assess the likelihood of supercells producing long-lived, intense tornadoes. It focuses on the expected type and intensity of tornadoes, particularly those capable of significant damage. A PDS watch often indicates a major tornado outbreak is likely within the watch area.
Protecting Yourself During a PDS Tornado Watch
When a PDS tornado watch is issued for your area, take the threat seriously and prepare to act quickly. Developing a family emergency plan with a designated safe shelter location is a practical first step. Safe shelter options include a basement, storm cellar, or an interior room on the lowest floor of a sturdy building, away from windows.
An emergency kit should be readily available. This kit should contain essentials such as bottled water (one gallon per person per day for at least three days), non-perishable food, a first-aid kit, a flashlight with extra batteries, and a battery-powered NOAA Weather Radio. A NOAA Weather Radio provides continuous weather information directly from the National Weather Service, which can be life-saving during power outages or when other communication methods fail. Staying informed through reliable sources like NOAA Weather Radio, local news, and NWS alerts helps ensure timely updates and warnings.