Radar blind spots happen for two main reasons: mountains and hills physically block the radar beam from reaching certain valleys, and the beam itself rises higher above the ground the farther it travels from its source, meaning distant locations only ever get a view of the upper part of a storm.

Terrain Blockage: When the Beam Can’t Get There

Radar beams travel in a mostly straight line and can’t bend around a mountain range. A valley on the far side of a ridge from the nearest radar station may simply never receive a usable signal at all, creating a permanent coverage gap regardless of how the weather is behaving that day. This is a well-known limitation across mountainous regions like parts of the western United States, where radar coverage maps show visible holes.

The Curve of the Earth Adds Up Over Distance

Even on flat terrain, the radar beam has to angle slightly upward to avoid hitting the ground close to the tower, and both that angle and the Earth’s curvature mean the beam keeps climbing the farther it travels. By around 100 miles from a station, the beam may be scanning several thousand feet above the surface, high enough to miss shallow rain or snow entirely, a problem explored further in our piece on radar and snow accuracy.

How to Compensate

Overlapping coverage from neighboring radar stations, which is exactly how a national network like NEXRAD is designed, fills in many of these gaps. When checking a live rain map in a known low-coverage area, it helps to cross-check against a secondary data source, such as a rain gauge network or a nearby webcam, rather than trusting a single radar frame completely.

In Conclusion

Radar is remarkably good technology, but it isn’t magic, and it can’t see through a mountain or perfectly resolve a storm hugging the ground 100 miles away. Knowing where the blind spots are helps you read the map more critically instead of less confidently.