Transparent Methodology
Every HailScore is built from verified NOAA radar data. Not estimates, not models. Here is exactly how we turn 4.7 million NOAA radar records plus live MRMS, NWS, SPC, and CoCoRaHS feeds into a hail-risk score for your address.
4.7M+
Radar Records
NOAA NEXRAD hail events
<2 hr
Live Radar
MRMS to your report
10+ Yrs
of History
2015 to present
$0
Your Cost
Always free for homeowners
HailScore is built on official NOAA government data, 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 four 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 measures estimated hail diameter and logs the event with precise coordinates and timestamp.
The SWDI API provides finalized NEXRAD hail-signature records once NOAA's quality-control pipeline runs (~60-90 day lag). We ingest every record ≥0.75″ across all 50 states. 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.
The Storm Prediction Center publishes Local Storm Reports (ground-truth observations from spotters, emergency managers, law enforcement) within hours of an event, and finalized Storm Events records on a 60-90 day cycle. We use both to validate radar detections and to anchor the largest events in our scoring.
A volunteer-staffed precipitation observation network used by NWS, USDA, and academic researchers. CoCoRaHS observers record hail size at their specific property after every event, 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 damage risk.
Weight breakdown
We count every radar-detected hail event within 15 miles of your property over the past 10 years. More events = higher base score.
Recent storms score higher than old ones. We apply an exponential time decay function. A storm from last month counts roughly 3x more than one from five years ago.
Hail size scales non-linearly. Under 0.75 inches is negligible. 1 to 1.5 inches is moderate. 1.75 to 2 inches is significant. Over 2 inches means severe structural damage likely requiring full replacement.
Repeated moderate hail compounds over time. A roof hit by 1" hail five times has accumulated more damage than one hit once by 2" hail.
A storm 0.1 miles away scores at full weight; one at 14 miles scores at roughly 10% weight. We use a distance-decay function based on storm cell size from NEXRAD data.
HailScores range from 0 to 100. Here is what each band means for your property.
0-30
Low Risk
Minimal hail history. Standard roof maintenance is sufficient.
31-60
Moderate Risk
Some hail activity. Consider an inspection after any 1"+ event.
61-80
High Risk
Regular hail exposure. Professional inspection strongly recommended.
81-100
Very High Risk
Severe, repeated hail history. Roof damage is likely. Inspect immediately.
From NOAA radar detection to your HailScore. The data pipeline explained.
Every four hours, our GitHub Actions pipeline pulls the latest MRMS MESH_Max_1440min GRIB2 grid from NCEP, decodes it with NOAA'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 PostGIS spatial queries: radar_hail (finalized SWDI), mrms_mesh (live MRMS), storm_events (NOAA), SPC LSR, CoCoRaHS, and NWS alerts. All scoped to within 8 miles of your property. Results come back in 200-500ms.
The five scoring factors (frequency, recency, hail size, cumulative damage, proximity) are computed in real time. MRMS events are deduplicated against radar_hail to prevent double-counting in the overlap window. Roof age and material apply final multipliers. 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 so you can verify anything that matters.
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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