What is MESH (Maximum Estimated Size of Hail)?

MESH comes from NOAA's Multi-Radar/Multi-Sensor (MRMS) system, which merges the national radar network into one 3D picture. For each location MRMS computes the Severe Hail Index (SHI):

1. Radar reflectivity between 40 and 50 dBZ is converted to a hail kinetic-energy flux.
2. That flux is summed vertically from the freezing (0°C) level to the storm top.
3. Heights near and above the -20°C level get extra weight, because that is where hail grows.
4. MESH is then estimated from SHI (Witt et al. 1998: MESH = 2.54 x SHI^0.5, in millimeters).

The freezing and -20°C heights come from weather model analyses. The grid is 0.01 degree (about 1.1 km north-south), and the product updates every 2 minutes. NOAA also publishes running maximum products over 30, 60, 120, 240, 360 and 1,440 minutes; the 24-hour (1,440-minute) maximum is the usual basis for daily hail maps.

• It tends to find hail that is never reported. Wendt and Jirak (2021) found MESH reveals hail in sparsely populated areas such as the High Plains, where few ground reports exist.
• It can overestimate severe hail somewhat. The same study describes MESH as designed to maximize detection of severe hail and likely overestimating it to some degree.
• It can underestimate in some storms, such as strongly sheared or tilted storms, left-moving supercells and storms with low-density hail (NOAA WDTD).
• Large sizes are least reliable. Ortega (2018) compared MRMS against more than 21,000 high-density ground reports: the best threshold for detecting severe (1 inch) hail was MESH of about 30 mm, and no MESH product showed real skill for hail of 2 inches or more. Reliability falls further as estimates approach 4 inches.

In practice, MESH is best at showing where hail fell and its relative size across a storm. Ground reports, soft-metal dents and inspections confirm the size at a specific property.

Storm statistics use the convective day: 12:00 UTC to 11:59 UTC the next morning (6 or 7 a.m. Central time, depending on daylight saving). That is how the Storm Prediction Center counts storm reports, and it keeps an evening storm from being split across two calendar dates. Hail Pro labels each storm day with the date on which it starts.

• Hail Pro ingests MRMS hail data every 30 minutes, so swaths appear while a storm is still moving and are finalized after the storm day ends.
• Swaths are drawn as contour bands of estimated size in quarter-inch steps from 1 inch, so you see the core of the storm, not just its outline.
• Each swath is intersected with property parcels, so you can list every home inside a band and filter by roof permit history and year built.
• Hail Pro's hail maps report the contour band rather than a single raw maximum value.