Hello from the outside: heat domes impeding radio and other signals in US midwest
Get the Energy newsletter
Daily energy & climate — solar, EVs, oil, the policy fights and tech bets shaping the transition. Free.
- Huntington County, Indiana outdoor emergency sirens activated at 3am on July 1 with no storm nearby, triggered by radio signals from 300 miles west in Iowa that matched the activation code, according to deputy emergency management director Thomas Fuller.
- Ohio motorists reported hearing radio stations from hundreds of miles away or losing coverage entirely during the same heat dome event, with no local emergency to explain the disruption.
- The phenomenon — tropospheric ducting — creates "tunnels in the sky" through which radio waves bounce, driven by temperature, air pressure and humidity; it affects radio, TV, radar, pacemakers, internet routers, satellites and cell phones, with 5G networks especially vulnerable because they operate at higher frequencies, per amateur radio operator Kyle Spillane of Jefferson City, Missouri.
- A 2023 study concluded that human-caused climate change makes extreme heatwaves at least 150 times more likely; the June–July 2021 Pacific Northwest heat dome caused an estimated 1,200 deaths in Washington state, Oregon and British Columbia.
- The US Forest Service said its firefighters experience "little to no impact" to radio systems from heat, though the spokesperson did not directly address whether tropospheric ducting interferes with their communications.
- Emergency managers worry about alert fatigue after repeated false alarms, a concern Fuller said "happened three or four years ago" with signals from different places, and one that already eroded trust in warning sirens at a Washington state community downstream of a major dam.
Why it matters: With researchers predicting more frequent and extreme heat domes over high-population regions, the Indiana false alarm exposes how tropospheric ducting can convert remote radio signals into mistaken local emergencies — and emergency managers say that growing pattern of false sirens risks training the public to ignore real warnings.
