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Weather Radar Gaps: Why They Exist And The Related Risk Factors

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The vast radar network across the United States is of the highest quality in the world, yet still has limitations. There are 160 radar sites covering the United States and its territories. Most of the sites are operated by the National Weather Service, but the Department of Defense also maintains and operates weather radar sites on military installations.Even with all these locations, there are still areas in the United States not covered by radar and weather experts have to adapt to that missing technology and find other means of weather observations for both public safety and business management efficiencies. With all of the technology and innovation available to us, why do these gaps in radar coverage still exist and is anyone doing anything about it?

Let’s start with a bit of history. The deployment of “Next Generation” (NEXRAD) radars in the early 1990s was a major step forward in being able to sample precipitation and detect severe storms across the continental United States. However, there are still some limitations within the dense radar network, primarily driven by geography. Specifically, due to the curvature of the earth, radar beams cannot see the entire atmosphere as the horizontal beam coming out from the radar increases with height as it moves further from its origin. The current radars have a range of 143 miles for highest resolution and can be extended to 248 miles in a long-range/lower resolution version.

Major population centers are fortunate to have the highest of quality radar data available for forecasters, but in some spots in the Plains or Mississippi River Valley the radar beam is only sampling data from 6,000-10,000+ feet above the ground. Missing out on lower parts of a thunderstorm, for example, is critical in severe weather, as the rotation from a tornado is strongest and more crucial below 5,000 feet. The radar is also limited in places with high terrain, as it is interrupted or blocked by mountain peaks. In addition to the curvature of the Earth, the radar beam weakens as it moves outward due to scattering and absorption, a process called radar beam attenuation. Radars are expensive to implement and maintain, so adding to this network will take long-term planning and budgeting. 

In addition to the existing network of government-managed radars, there are a few universities around the country that have recently installed a radar to help fill gaps where their university is located. For example, through donations and grant money, Western Illinois University recently installed a weather radar to help fill the void in northeastern Missouri and western Illinois, one of the larger gaps in the current network. Just down the road, the University of Missouri has its own radar as it also is in a radar gap. 

To fill in the radar gaps, forecasters use ground observations such as weather stations, trained weather spotter reports and mPING observations to connect the dots in between radar sites. mPING (Meteorological Phenomena Identification near the Ground) is an initiative implemented in by NOAA’s National Severe Storms Laboratory as a way to collect public weather reports; it’s essentially the Waze for weather. Forecasters also use satellite data, which has recently been upgraded to provide a new scan every minute in most spots.

Reports are not enough when limitations exist, especially during severe weather cases and minutes matter where the situation is dynamic. Furthermore, radar gaps also hurt businesses that rely on hail data from thunderstorms to be proactive in their operations and deployment. If the radar measures hail 10,000 feet above the ground, there is no way of knowing if it reached the surface, except for ground observations. Those are quite spotty and incomplete. As sophisticated as weather radars have become, forecasters have to find creative solutions to deal with the limitations within the seemingly dense radar network. 

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