MESH Explained: Hail Size Estimation for Property Claims
By StormAuditor Editorial Team · Published 2026-07-14 · Updated 2026-10-07
Based on public NOAA and National Weather Service records, published under StormAuditor's methodology and data-source standards. Radar-derived hail sizes are estimates unless attributed to a ground report.
Damage-threshold ranges in this article are general guidance synthesized from industry and federal research — IBHS building-performance research, NWS severe criteria, and product standards such as UL 2218 (hail impact resistance) and ASTM D3161/D7158 (shingle wind ratings). Actual performance depends on product rating, age, installation quality, exposure, and impact characteristics — thresholds describe when damage becomes possible, not when it occurs.
MESH is a radar estimate of the largest hail that reached the ground, computed by NOAA's MRMS system on a grid of about 1 km. StormAuditor uses the MESH value in the grid cell that contains a property, and a ground report within 3 miles can raise it up to the largest radar value nearby.
MESH (Maximum Estimated Size of Hail) is a radar estimate of the largest hail that reached the ground at a location. NOAA's Multi-Radar Multi-Sensor (MRMS) system computes it on a grid of about 1 km across the United States, so it gives a hail size estimate for places no spotter saw, including the cell that contains a property.
How MESH is calculated
MESH comes from the Severe Hail Index: radar reflectivity weighted through the part of the storm that is below freezing, where hail grows (Witt et al. 1998). The algorithm converts that index to an estimated maximum hail diameter at the ground, calibrated against ground hail reports.
- Reflectivity. Large ice returns a strong radar signal. Reflectivity high in the storm, above the freezing level, is what MESH weights most.
- Temperature profile. The freezing and -20 °C heights from model data set which layer of the storm counts.
- Many radars at once. MRMS merges every NEXRAD radar that sees a storm, so one estimate covers each grid cell.
Forecasters also read dual-polarization fields such as differential reflectivity and correlation coefficient to spot hail, but operational MESH is not computed from them.
What a MESH value means
A MESH value is an estimate of the largest stone in that grid cell, not the typical stone and not a count. Published verification scores MESH by size category, so treat the size class (below 1.00 in., 1.00 in. or larger, 2.00 in. or larger) as the reliable signal and the decimal as the algorithm's point value. StormAuditor prints MESH values unrounded.
Ground reports and MESH answer different questions, and they can differ on the same day. StormAuditor's state recaps show both:
- In Washington, radar estimated hail to 1.78 in. on May 28, 2026, the day of the state's largest ground hail report in the 12 months through August 25, 2026: 1.75 in. near Odessa (Washington recap).
- In Missouri, radar MESH peaked at 2.96 in. on April 28, 2026, while a broadcast media report from 5 SE Bois d'Arc put hail at 4.75 in. The highest MESH in Missouri in the 12 months through September 24, 2026, 3.63 in. on May 16, 2026, came on a day whose largest ground report was 3.0 in. (Missouri recap).
How StormAuditor uses MESH
StormAuditor's hail engine (SAHE-2) applies one rule. The estimate is the MESH value in the radar grid cell that contains the property. A ground hail report (NWS Local Storm Report) within 3 miles on the same date can set a higher value, capped at the largest radar value within 3 miles. Warnings, and reports farther than 3 miles, are shown as context and do not change the estimate.
The MESH archive stores cells of 0.50 in. and larger, so a value below 0.50 in. at the property means the radar estimate in that cell was below half an inch. The hail methodology explains the rule and the research behind the 3-mile limit.
Where to see MESH on StormAuditor:
- The Free Report Snapshot gives a YES or NO for estimated hail of 0.75 in. or larger at an address in the last two years.
- A Hail Report lists every qualifying storm date at one address with the estimated maximum hail size.
- The Audit Report shows the MESH value at the property and nearby, the ground reports, and the arithmetic for one date.
- On Pro+ plans, the Hail Explorer maps statewide MESH swaths by date in nine bands from 0.50 in. to 3.00 in. and up.
Limitations of MESH
- Estimate, not measurement. MESH is computed from radar, not from stones on the ground. Melting, wind drift and storm tilt can put hail a few kilometers from where radar places it.
- Beam height. Far from a radar, the beam samples high in the storm, and in parts of the intermountain West it can overshoot low storms. An absence of MESH there is weaker evidence than the same absence near a radar.
- Wet hail and intense cores. MESH can under-estimate wet hail and over-estimate hail in very high reflectivity cores.
- Grid size. Each value covers a cell of about 1 km, not a single roof.
See Limitations and Data Sources for the full list.
Frequently asked questions
Does MESH account for hail melting before it reaches the ground?
MESH is calibrated against ground hail reports, so it estimates hail size at the ground. Melting during the fall varies from storm to storm, so the size observed at the surface can still differ from the estimate.
Can MESH tell me how many hailstones hit my property?
No. MESH estimates the size of the largest hail in a grid cell. It says nothing about the number of stones or how long the hail lasted.
How far back does StormAuditor's MESH data go?
Address-level hail estimates go back to October 2021. NOAA storm records on StormAuditor's state and city pages go back to January 2010.
If MESH shows large hail, does that mean my roof is damaged?
No. A large MESH value at an address shows that radar estimated large hail there; whether a roof was damaged is decided by inspection. MESH is evidence about the storm, not about the roof.
Why can a ground report be larger than MESH?
A spotter reports the largest stone at one point, and MESH estimates a 1 km cell from radar. Within a cell, the largest stones can exceed the estimate, which is why StormAuditor lets a ground report within 3 miles raise the estimate up to the largest radar value nearby.