"Wet bulbs" helping Hennepin County emergency crews keep people safe amid dangerous heat

PLYMOUTH -- Hennepin County is relying on a growing network of special weather stations to aid emergency managers in planning for and responding to heat-related emergencies.

"We want to know in what areas are going to require the greatest amount of resources," said Eric Waage, the county's director of emergency management. "Typically they're the areas with disparities and folks lacking air conditioning who face challenges, but there are also areas with exceptionally high heat island effects."

According to Waage, a heat island is an area where conditions on the ground, including architecture and topography, may make it a hotter spot versus some others. 

The special tool to pick up those readings is much more than a typical thermometer - a "wet bulb." The actual instrument is a black globe about the size of a softball and it includes a moisture wick inside to simulate how a human body might react in direct sunlight, as opposed to standard thermometers that are usually placed in the shade.

"What we're about is the safety of human lives," Waage said. "This is more accurate in depicting how effectively each person can cool themselves than, say, heat index which only takes in temperature and humidity."

Currently there are about 20 such weather stations across Hennepin County, with at least five more budgeted for the future. The plan is to have one weather station per 2.5 mile radius.

The data is shared in real time with hospitals, EMS crews, law enforcement and fire departments. 

"This heightens awareness. It could result in shifting a schedules, maybe loading up certain areas under greater threat with more crews," Waage said.

"This also has a long-term mission. Over and over and over again we're looking at this data seeing where is consistently hotter than other places so we can redouble our efforts to find cooling centers and locations."