A storm wakes you at night, then disappears. Months later, someone asks when it hailed and how big the stones were. Witness reports and radar estimates each supply part of the answer, but neither automatically proves the size of hail that reached one roof.
How a thunderstorm makes hail
An updraft lifts raindrops into air below freezing. Hailstones grow as liquid droplets collide with them and freeze onto their surfaces. They fall when the updraft can no longer support their weight.
Stronger updrafts can support larger stones. Hail two inches across or larger is generally associated with supercell thunderstorms. The useful picture is growth within a strong updraft; it does not require imagining every stone repeatedly cycling up and down.
A ruler beats a coin comparison
Common hail comparisons are a penny at three-quarters of an inch, a quarter at one inch, a golf ball at one and three-quarter inches and a baseball at two and three-quarter inches. One inch is the National Weather Service severe-hail threshold.
Those familiar objects are helpful, but estimates cluster at their sizes. A stone between a quarter and a golf ball may be reported as either. A ruler, calipers or tape measure gives a more useful measurement than rounding to a familiar object.
No report does not mean no hail
A ground report needs someone to observe, measure and report the hail. Sparse populations leave gaps, and nighttime storms can pass without witnesses. Even when someone reports hail, they may not have found the largest stone.
For that reason, an empty patch on a report map is incomplete evidence. It cannot establish that every house in that patch escaped hail. It records what people reported, not every stone that fell.
What MESH can and cannot tell you
MESH means Maximum Estimated Size of Hail. It uses radar reflectivity above the atmospheric freezing level to estimate hail size. Radar can sample storms at night and where no observer is present, subject to coverage and beam-height limits.
The original algorithm was calibrated so about 75% of observed hail sizes fell below the radar estimate. That is a calibration result, not a guarantee about any individual storm. An estimated 1.8-inch maximum does not prove that 1.8-inch stones landed at your address.
The most useful record keeps time, track and radar estimate together, then distinguishes them from a ground measurement or property inspection. A radar estimate can start an investigation; it does not finish one.
What to take away
Use these checks next time:
- Record when and where the storm passed.
- Keep radar-estimated size separate from a measured hailstone.
- Treat a storm record as context, not an inspection or proof of damage.
