Transparent Methodology
Every HailScore is built from public hail data — finalized radar, ground reports, and live MRMS. Here is exactly how we turn the hail records near your address, from a record set of 41.2M+ hail records across government sources (8.8 million NOAA NEXRAD radar records, plus MRMS radar, NOAA Storm Events, SPC, and CoCoRaHS reports), into a hail exposure score for your address, with any active NWS warning shown alongside it.
41.2M+
Hail Records
All NOAA-linked sources
8.8M+
NEXRAD Radar
SWDI hail signatures
~2 hr
Live Radar
Typical MRMS to your report
$0
Your Cost
Always free for homeowners
HailScore is built on public NOAA and NWS data plus CoCoRaHS volunteer reports, the same data used by meteorologists, insurance actuaries, and the National Weather Service.
NOAA's MRMS system fuses every NEXRAD radar in the US into a continuous CONUS-wide hail-detection grid updated every two minutes. We ingest the MESH_Max_1440min product — maximum estimated hail size over the last 24 hours — directly from NCEP every two hours. This is what closes the gap between when a storm hits and when your score reflects it.
The Next Generation Weather Radar network operates 160 high-resolution Doppler radar stations across the US. Dual-polarization technology detects precipitation type, intensity, and movement. When storm cells produce hail, NEXRAD estimates the maximum hail size and logs the event with precise coordinates and timestamp.
The SWDI API provides finalized NEXRAD hail-signature records as NOAA's quality-control pipeline publishes them — most within days of the storm, some finalizing over the following weeks. We ingest these records across all 50 states, refreshed weekly. Combined with live MRMS, this gives us continuous coverage with no gap between historical and current data.
The NWS API publishes every Severe Thunderstorm Warning and Tornado Warning as a polygon geometry with parsed maximum hail size and wind gust. We poll the active-alerts feed every 60 seconds during hail season. When a polygon covers your address, the report shows a live banner above the score.
NOAA's Storm Events Database is the finalized national record of hail observed on the ground — stone sizes as reported by trained spotters and NWS staff, published months after the storm (typically 2-4). Alongside it we hold NOAA's severe-weather hail archive for Colorado: a point-in-time load covering 1955 through 2023, not a live feed. When one of those ground reports sits near a radar detection of the same storm, your score uses the observed size in place of the radar estimate. SPC Local Storm Reports — the preliminary accounts filed during a storm — are ingested weekly and counted in our public record total, but the score reads the finalized records, not the preliminary ones.
A volunteer-staffed precipitation observation network used by NWS, USDA, and academic researchers. CoCoRaHS observers report hail at their own locations when it falls, providing ground truth at finer spatial resolution than SPC reports.
Five weighted factors combine to produce your 0 to 100 HailScore. Each factor reflects a distinct dimension of hail exposure.
The factors
Hail size is weighted on a power curve, so larger stones add disproportionately more to the score than smaller ones. Around 1 inch is where asphalt shingles can begin to bruise or crack, and at 2 inches and above a roof inspection is the normal next step after a storm. The weight is exposure, not a finding about any particular roof.
We count qualifying radar-detected hail events near your property over the past 10 years. More events raise the base score, with diminishing weight as the count climbs.
Recent storms score higher than old ones. We apply an exponential time decay, so a storm from last year weighs more than one from a decade ago.
Repeated moderate hail compounds over time. A roof hit by 1" hail several times has accumulated wear a single larger event might not produce.
A storm directly over your property counts at full weight; contribution falls off steeply with distance, because hail swaths are narrow and damage attenuates fast beyond the core.
HailScores range from 0 to 100. Here is what each band means for your property.
0-25
Low Risk
Minimal hail history. Standard roof maintenance is sufficient.
26-50
Moderate Risk
Some hail activity. Consider an inspection after any 1"+ event.
51-75
High Risk
Regular hail exposure. Professional inspection strongly recommended.
76-100
Very High Risk
Severe, repeated hail history — very high exposure. Inspect immediately.
From NOAA radar detection to your HailScore. The data pipeline explained.
Every two hours, our GitHub Actions pipeline pulls the latest MRMS MESH_Max_1440min GRIB2 grid from NCEP, decodes it with ECMWF's ecCodes library, filters to CONUS land cells ≥0.75″, and writes to our PostGIS database. A second writer runs on a backup machine in parallel for redundancy.
During hail season we poll the NWS active-alerts feed every 60 seconds. Severe Thunderstorm Warnings and Tornado Warnings get stored with their polygon geometry, parsed max hail size, and expiration. When you look up an address, we run a point-in-polygon query — if a warning covers you, the report shows it.
Your address is geocoded via Mapbox to lat/lon coordinates. We then run parallel spatial queries across all six data sources — finalized SWDI radar, live MRMS, NOAA Storm Events, CoCoRaHS, the SPC hail archive, and NWS alerts. Most are scoped to within 8 miles of your property; the SPC archive is read at 15 miles, and an NWS warning matches when its polygon covers your address. Results come back in 200-500ms.
The scoring factors are computed in real time. Overlapping live-MRMS and finalized-radar detections are de-duplicated to prevent double-counting. Roof age and material apply final adjustments. The score is normalized to a 0–100 scale.
Your report builds in the browser with the score gauge, an interactive Mapbox map (with optional hail-swath polygon overlay for pros), event timeline, recent MRMS activity panel, storm narrative, and source citations. Each section names the data feed it came from.
Need documentation for an insurance claim, real estate transaction, or legal proceeding? Order a source-cited storm-history PDF for $9.95. Every hail event is cited back to its NOAA Storm Events record number, NEXRAD radar station ID, and NWS warning polygon ID — the same sources your insurance company will reference. Delivered to your inbox in approximately 60 seconds.
Now that you know how it works, enter your address and see exactly what storms have hit near your home. Free, instant, no signup required.
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