Inside Report: Weather alert thresholds can vary

“Hazardous weather” can mean different things to different people, and in recognition of this, the National Weather Service in Slidell is working to implement a more targeted automated alert system for their service area in Southeast Louisiana and parts of Mississippi.

Ken Graham, meteorologist-in-charge with the National Weather Service in Slidell, explains that although the office issues alerts on severe weather, the threshold of when that alert is sent might not meet local or special needs.

Graham said National Weather Service alerts are designed to be protective of life and property, but there could be times when information below those thresholds could be beneficial.

For example, the National Weather Service might not send out a dense fog advisory until there is a half-mile of visibility or less, but the state Department of Transportation and Development might want to take action before that trigger point is reached.

In order to tailor alerts more to individual agencies, cities, parishes and other groups, staff at the National Weather Service’s Slidell office have visited emergency management officials in their service area to create an Impact Catalog.

This Impact Catalog lists thresholds where action would be necessary but might be different from the National Weather Service thresholds.

Take wind, for example.

Say a city or parish is holding a music festival and tents are rated to a certain wind speed. Even if winds don’t trigger an official high wind warning from the National Weather Service, if it reaches a level set by the city or parish for safety reasons, the system would send an automatic alert to that city or parish.

It would give parish mangers a notice that there could be a problem and they could act on that information.

“You don’t have to have a warning to take action,” Graham said.

For another example, take Interstate 12. It’s a typical day and there is a 40 percent chance of thunderstorms forecast, which would be pretty normal for a south Louisiana summer day.

However, if the National Weather Service can tell State Police that the 40 percent chance of thunderstorms will impact a large section of Interstate 12 between 3 p.m. and 7 p.m. does that mean something different?

“The answer is yes. That’s rush hour,” Graham said.

That type of information could help law enforcement and emergency responders better prepare for possible problems.

Graham said they met with emergency managers about any possible trigger points — whether that be schools or industry or parish activities.

“Then we’ll look at gaps and may have to revisit some places,” Graham said.

Graham said he hopes the system will be up and running by summer.

Although the program won’t initially include everyone, he said, the beauty of the system is once it’s set up, more information can be fed in over time.

“It’s always going to be incomplete. There will always be something we won’t have and need to continuously update and add new impacts,” he said. “We can build on this forever.”

The effort is part of a larger pilot program called an Impact-Based Decision Support which includes the ability to deploy National Weather Service staff and the office’s Significant Weather Emergency Response Vehicle to things like the NCAA Final Four weekend, hurricanes and tropical storm events and the Superbowl.

Amy Wold covers the environment for The Advocate. Follow her on Twitter @awold10.