What is a PDS tornado watch? Understanding the label that describes 'rare situations' for tornadoes
The Midwest, including portions of Iowa, was under a “particularly dangerous situation tornado watch” on May 21.
When the National Weather Service's Storm Prediction Center in Norman, Oklahoma issued a tornado watch for the majority of Iowa around 1:15 p.m. Tuesday, it applied the special PDS label. The watch covered all but the farthest western counties in Iowa, which were already covered by another tornado watch, issued without the PDS label, around 11:15 a.m. Tuesday.
In Iowa, multiple rounds of storms passed through the state, causing destruction, including multiple deaths, in the small town of Greenfield.
PDS is a label used in situations when “there’s an expectation of particularly violent tornadoes possible,” said Andy Ervin with the National Weather Service's office in the Quad Cities.
That can also be used in the case of a derecho because of the widespread, high winds, Ervin said.
Updates: Tornado, storm damage still being felt in Iowa as clean up begins
How does the National Weather Service define a PDS tornado watch?
The National Oceanic and Atmospheric Administration’s glossary defined a PDS watch as “rare situations when long-lived, strong and violent tornadoes are possible.”
You may see this label applied to watches when there’s a moderate or high risk of severe weather (the two highest categories used to describe severe weather) forecasted by the Storm Prediction Center, though it’s not “impossible” to have a PDS watch occur at a lower risk level, Ervin said.
More: How do tornadoes form? Explaining the severe weather after dozens of recent Iowa tornadoes
What does a tornado watch mean vs. a tornado warning?
Northern & Central New Mexico: Let’s TACO about the difference between a watch & a warning. 🌮🌮
Kidding aside, a watch means conditions are favorable for severe weather/flooding to develop while a warning means severe weather/flooding is occurring! Stay weather alert. #NMwx pic.twitter.com/GHZffUUJRm— NWS Albuquerque (@NWSAlbuquerque) June 29, 2021
A watch is when you should plan and prepare. A warning is when it's time to take action.
That’s because the former is to alert you that conditions are favorable for severe weather, and usually, a watch encompasses a large area where such conditions could occur. When there is a warning for severe weather, it’s time to get yourself to a safe location to shelter from, for example, a tornado.
Paris Barraza is a trending and general assignment reporter at the Des Moines Register. Reach her at pbarraza@registermedia.com. Follow her on Twitter @ParisBarraza.
This article originally appeared on Des Moines Register: What is a PDS watch? See the different watches, warnings for tornaodes
