StormerSite Reference
Our Data & Methodology
How we collect, verify, and present severe weather data across the United States.
Where Our Data Comes From
StormerSite aggregates severe weather data exclusively from official United States government sources. Every storm report, radar signature, and verification record originates from federal agencies tasked with monitoring and documenting severe weather. We do not use crowdsourced platforms or unverified third-party data. Our three primary data pipelines are the NWS Storm Prediction Center, the national NEXRAD radar network, and NWS Storm Data publications, which include trained spotter reports and post-storm surveys.
NWS Storm Reports
The Storm Prediction Center (SPC), a division of NOAA's National Weather Service, maintains the nation's real-time severe weather reporting system. When a severe weather event occurs, local NWS Weather Forecast Offices (WFOs) issue Local Storm Reports (LSRs) that are forwarded to the SPC and compiled into a national feed.
These reports cover three categories of severe weather: hail (1″ diameter or greater), wind (58 mph or greater, or any wind damage), and tornadoes. Each report includes the event time, location coordinates, magnitude, and the source of the report.
StormerSite ingests these reports directly from the SPC and processes them into our database, preserving all original metadata including geographic coordinates, reported hail size, wind speed, and source attribution. Reports appearing on our Today and Yesterday pages reflect this pipeline, typically within minutes of the SPC publishing them.
SPC Today's Storm Reports • National Weather Service • NCEI Storm Events Database
NEXRAD Radar Network
The NEXRAD (Next-Generation Radar) network consists of approximately 160 high-resolution S-band Doppler weather radar stations operated by the National Weather Service, FAA, and Department of Defense. These radars provide continuous volumetric scans of the atmosphere across the contiguous United States, detecting precipitation type, intensity, and motion.
StormerSite processes NEXRAD data to build our hailtracks database, a record of radar-indicated hail signatures indexed by time and geographic coordinates. This database currently contains over 44 million rows of radar-derived hail observations, allowing us to identify hail corridors, frequency patterns, and severity estimates at a granular level across the country.
Radar-indicated hail differs from ground-truth spotter reports. A radar signature tells us that a storm was producing hail aloft with estimated size at a given time and location; a spotter report confirms what actually reached the ground. Both are valuable, and StormerSite uses them as complementary layers.
Trained Spotters & NWS Storm Data
The NWS SKYWARN program trains volunteer severe weather spotters across the country. These spotters provide ground-truth observations during active severe weather, including measured hail size, wind damage assessments, and tornado sightings. Their reports are relayed through local Weather Forecast Offices and become part of the official Local Storm Report record.
After events conclude, NWS offices conduct post-storm surveys and compile verified data into NOAA Storm Data, the official publication of record maintained by the National Centers for Environmental Information (NCEI). Storm Data entries undergo editorial review and represent the most authoritative account of each event.
StormerSite incorporates both real-time spotter reports and post-event verified data to provide layered confirmation. When you see a report on our site, the source field tells you whether it originated from a trained spotter, law enforcement, emergency management, or another qualified observer.
Understanding the Hail Frequency Rating
On each city hail report page, you'll see a Hail Frequency panel in the summary bar at the top. This rating tells you how often a city typically experiences hail based on its historical record of SPC storm reports.
The rating is calculated from the annual average number of hail reports within 10 miles of the city, using SPC Local Storm Report data going back to 2004. We divide the total number of hail reports by the number of years in the record to produce a simple annual average, then assign a frequency label based on where that average falls.
6 or more hail reports per year on average.
3 to 5 hail reports per year on average.
1 to 2 hail reports per year on average.
Less than 1 hail report per year on average, but at least one report exists.
No hail reports in the record for this area.
The Hail Frequency rating is based entirely on the annual average of SPC Local Storm Reports, ground-truth hail reports collected by the National Weather Service since 2004. It reflects how often hail has been reported near a city, not how often hail has actually fallen. Rural areas with fewer observers will naturally generate fewer reports than urban areas.
This rating describes historical frequency only. It is not a forecast, not a risk assessment, and should not be used as the sole basis for insurance, roofing, or property decisions.
Data Processing & Integrity
All data on StormerSite is sourced from U.S. government agencies, primarily NOAA, the National Weather Service, and the National Centers for Environmental Information. We do not generate, fabricate, or editorially modify storm report data. Our processing pipeline handles ingestion, geocoding normalization, deduplication, and indexing, but the underlying observations remain as reported by their original sources.
Storm reporting is inherently imperfect. Not every hailstone that falls is observed. Not every radar signature corresponds to hail reaching the ground. Rural areas are underreported relative to urban areas. We acknowledge these limitations transparently throughout the site, including in the disclaimers on each city page.
If you have questions about our data or methodology, please contact us.