NOAA Hail Data Explained What It Actually Means For Your Roof

When Shingleprint shows you "4 hail events detected near your address," where does that number come from? What does it actually mean? And why might it differ from what you remember experiencing?

Here's a plain-English explanation of what NOAA NEXRAD hail data is, how it's collected, and what its limitations are.

What Is NOAA NEXRAD?

NEXRAD stands for Next Generation Radar. It's a network of 160 Doppler radar stations operated by NOAA, the US Air Force, and the FAA. The network covers virtually all of the continental US and has been operating since the early 1990s.

Every 4–6 minutes, each radar station sweeps its coverage area and measures the intensity of precipitation returns. For hail, the radar looks for specific reflectivity signatures that indicate large frozen particles. This data is processed and stored in NOAA's SWDI (Severe Weather Data Inventory) database, which is publicly accessible.

What NOAA Actually Measures

NOAA does not measure individual hailstones. It measures radar reflectivity — the intensity of the radar signal bouncing back from precipitation. Hail produces a distinctive return pattern that radar algorithms use to estimate hailstone size.

The key word is estimate. A "2.75 inch" reading means the radar algorithm calculated that hailstones of that size were likely present in that radar cell. Radar cells are roughly 1 square kilometer. The actual hailstone size at any specific house within that cell could be larger, smaller, or the same.

How We Process The Data

Shingleprint queries NOAA SWDI for 36 months of hail data within 1 mile of your coordinates. We filter to events where the radar-estimated hail size was at least 0.75 inches — that's quarter-sized, the threshold where asphalt shingles begin showing measurable damage. We then group all radar signals by storm day so that one storm that lasted 4 hours counts as 1 event, not 40 radar pings.

This gives you a count of storm days with confirmed damaging hail activity near your address — a much more useful number than raw radar signal counts.

What The Data Can't Tell You

• Whether hail actually hit your specific roof (vs. a nearby location)
• The exact size of hailstones at your address (radar estimates, not measurements)
• Whether your roof was damaged (depends on roof age, material, and prior condition)
• Anything about the last 4–5 months (NOAA data has an inherent latency period)

For those answers, you need a professional roof inspection. What the data does tell you is whether it's worth getting one.