NOAA Hail Data: What It Is and How to Use It for Your Home

If you have ever searched for hail history at your address, tried to verify a storm for an insurance claim, or wondered whether that loud noise at 3 AM was actually hail, you have probably encountered references to "NOAA data" or "NEXRAD radar." These terms get thrown around by insurance adjusters, roofing contractors, and weather professionals, but most homeowners have no idea what the data actually is, where it comes from, or how to access it.

This guide explains the NOAA hail data ecosystem in plain language: what NEXRAD radar is, what the SWDI database contains, how radar detects hail, and most importantly, how you can use this data to protect your home. We will also explain how HailScore transforms this raw government data into something any homeowner can understand and act on.

What Is NOAA?

NOAA stands for the National Oceanic and Atmospheric Administration. It is a federal agency within the U.S. Department of Commerce responsible for monitoring weather, oceans, and atmospheric conditions. NOAA operates the National Weather Service, maintains the nation's radar network, and archives decades of weather data.

For homeowners, the most relevant NOAA programs are:

NEXRAD — the nationwide radar network that detects hail in real time

SWDI — the database that archives severe weather events including hail

SPC — the Storm Prediction Center that collects ground-level storm reports

These three programs, working together, create the most comprehensive record of hail activity in the United States.

What Is NEXRAD and How Does It Detect Hail?

The Radar Network

NEXRAD stands for Next-Generation Radar. It is a network of 159 high-resolution S-band Doppler weather radar stations positioned across the United States and select U.S. territories. These stations were installed beginning in the 1990s and have been continuously upgraded since then.

Each NEXRAD station transmits pulses of microwave energy into the atmosphere. When these pulses encounter precipitation (rain, snow, hail, or sleet), some of the energy bounces back to the radar. By analyzing the returned signal, the radar can determine:

What type of precipitation is occurring

How intense it is

Where it is located (direction and distance from the radar)

How fast it is moving (using Doppler shift)

How Radar Distinguishes Hail from Rain

Here is where it gets interesting for homeowners. Hail and rain produce different radar signatures:

Reflectivity. Larger particles return stronger signals. Hailstones are significantly larger and denser than raindrops, so they produce much higher reflectivity values. Meteorologists measure reflectivity in units called dBZ (decibels of Z). Values above 50 dBZ typically indicate heavy rain or small hail. Values above 60 dBZ strongly suggest hail. Values above 65 to 70 dBZ indicate large, damaging hail.

Dual-polarization technology. Modern NEXRAD radars (upgraded between 2011 and 2013) transmit energy in both horizontal and vertical orientations simultaneously. This "dual-pol" capability lets the radar estimate the size and shape of particles in the atmosphere. Because hailstones tumble as they fall (unlike raindrops, which flatten into oblate spheroids), they produce distinctive dual-pol signatures that help the radar distinguish hail from heavy rain.

Hail Detection Algorithms. NEXRAD stations run automated algorithms that analyze reflectivity, dual-pol data, and atmospheric temperature profiles to estimate:

Probability of hail at a given location

Probability of severe hail (1 inch or larger)

Maximum estimated hail size

These algorithm outputs are what get archived in the databases that tools like HailScore analyze.

What NEXRAD Cannot Do

It is important to understand NEXRAD's limitations:

It detects hail in the atmosphere, not on the ground. Radar measures what is happening inside the storm cloud and below it, but small hailstones can melt before reaching the surface, especially in warm, dry environments.

Resolution is not rooftop-level. Each radar scan covers a volume of atmosphere, not a pinpoint. A single detection might represent conditions across an area of several hundred yards to a few miles, depending on distance from the radar station.

Terrain and distance affect accuracy. Properties far from a radar station or behind terrain features may have gaps in coverage. The radar beam rises as it travels outward, so distant observations are reading conditions higher in the atmosphere.

Despite these limitations, NEXRAD is far and away the best tool available for reconstructing hail history at any location in the United States.

What Is the SWDI (Severe Weather Data Inventory)?

The Severe Weather Data Inventory is a database maintained by NOAA's National Centers for Environmental Information (NCEI). It archives the output of NEXRAD's hail detection algorithms in a structured, searchable format.

What SWDI Contains

Each hail record in SWDI includes:

Date and time of the detection (in UTC)

Geographic coordinates (latitude and longitude) of the detection point

Maximum estimated hail size based on radar analysis

Cell ID linking the detection to a specific storm cell being tracked by the radar

Radar station that made the detection

This is the raw data that insurance companies, meteorologists, roofing contractors, and forensic weather analysts pull from when they need to verify whether hail occurred at a specific time and place.

How Big Is the SWDI Database?

The SWDI contains millions of hail detections going back decades. For the United States alone, the hail-specific records number in the tens of millions. HailScore has ingested 4.5 million radar-detected hail records that meet quality thresholds (hail size of 0.75 inches or larger) from the SWDI, covering approximately the last 10 years across all 50 states.

Can You Access SWDI Yourself?

Technically, yes. SWDI is a public database and NOAA provides a web interface and API for querying it. You can access it at ncei.noaa.gov/swdiws/. However, actually using the raw data is extremely challenging for non-technical users:

Queries require geographic coordinates, not addresses. You need to know your latitude and longitude, not your street address.

Results are in CSV or XML format. The output is raw tabular data, not a map or timeline.

No scoring or interpretation. SWDI gives you detections. It does not tell you what they mean for your property.

No integration with other data sources. SWDI provides radar hail detections only. It does not factor in wind, solar exposure, tree coverage, or roof characteristics.

The interface is built for researchers. NOAA's data access tools are designed for scientists and analysts, not homeowners.

This is exactly the problem that HailScore solves.

How HailScore Makes NOAA Data Accessible

HailScore takes the raw NOAA data (NEXRAD detections, SWDI archives, and SPC reports) and transforms it into something any homeowner can use in 30 seconds.

Here is what HailScore does that you cannot easily do yourself:

1. Address-to-Coordinate Translation

You type a street address. HailScore geocodes it to precise coordinates and searches the radar database for all hail detections within range. No latitude/longitude required.

2. Proximity Analysis

Not all hail detections near your address are equally relevant. HailScore weights detections by distance from your property. A detection 0.5 miles away is more significant than one 5 miles away. The algorithm produces a proximity-adjusted exposure score.

3. Severity Weighting

A 0.75-inch hail event is not the same as a 2-inch hail event. HailScore weights each detection by estimated hail size, recognizing that larger hailstones cause exponentially more damage.

4. Temporal Analysis

Recent events matter more than events from 10 years ago (because recent damage is more likely to still be present on your roof). HailScore applies time-decay weighting to produce a score that reflects current risk, not just historical frequency.

5. Multi-Source Integration

HailScore does not stop at radar data. It integrates 9 data sources including wind exposure, solar irradiance, tree canopy coverage, and property characteristics to produce a holistic risk assessment. This is why the HailScore is more useful than raw SWDI data alone.

6. Visual Presentation

Instead of rows in a spreadsheet, HailScore presents your data as:

A 0 to 100 score that anyone can understand

An interactive map showing hail events relative to your property

A storm timeline with dates, sizes, and distances

Street-level views of your property for context

What Insurance Adjusters Know That You Should Too

Here is something that gives insurance companies an advantage: they already use this data. When you file a hail damage claim, your insurer's adjuster (or their third-party vendor) will pull NOAA radar data to verify the claim. They will check whether hail was detected near your address on the date you are reporting damage.

If the radar data does not support your claim, it gets denied or reduced. If the data does support it, it strengthens your position.

The problem is that most homeowners do not know this data exists, much less how to access it. They file claims based on "I think there was a storm" and hope for the best. Meanwhile, the insurance company has the exact dates, sizes, and locations pulled from the same NOAA database.

HailScore levels this playing field. By checking your address at myhailscore.com before contacting your insurer, you walk into the conversation with the same data they have. You know the exact dates. You know the estimated hail sizes. You know how close the detections were to your property.

This is not about gaming the system. It is about being informed.

Understanding Hail Size in NOAA Data

NOAA data reports hail size in inches, estimated from radar analysis. Here is what the numbers mean in practical terms for your roof:

Less than 0.75 inches (Pea to Penny Size)

Below the threshold that NEXRAD's algorithms typically flag as significant. Unlikely to cause roof damage on most materials. HailScore's database filters at the 0.75-inch threshold.

0.75 to 1.0 inches (Penny to Quarter Size)

Small but potentially damaging hail. Can dislodge granules from asphalt shingles, especially on older roofs. Over multiple events, this cumulative damage adds up.

1.0 to 1.5 inches (Quarter to Golf Ball Size)

The range where functional roof damage becomes likely. Insurance companies typically consider hail at 1 inch or larger to be potentially damaging. Multiple events in this range can significantly reduce roof lifespan.

1.5 to 2.0 inches (Golf Ball to Hen Egg Size)

Significant hail that causes obvious damage to most roofing materials. Single events at this size warrant an insurance claim and professional inspection.

2.0 to 2.75 inches (Hen Egg to Baseball Size)

Severe hail that can crack shingles, dent metal, and break tiles. Events at this size are major weather occurrences that typically generate widespread insurance claims.

Over 2.75 inches (Baseball Size and Larger)

Extremely destructive hail. Can penetrate roof decking, shatter skylights, and cause structural damage. Fortunately, events at this size are relatively rare, though they do occur multiple times per year in hail-prone regions.

How to Look Up Hail History for Your Address

You have two options:

Option 1: The Hard Way (Direct NOAA Access)

Go to ncei.noaa.gov/swdiws/

Select the nx3hail dataset (NEXRAD Level-III Hail detections)

Convert your address to latitude/longitude coordinates

Construct a query with a bounding box around your coordinates

Specify a date range

Download the CSV results

Analyze the data yourself (filter by hail size, calculate distances, assess severity)

This process works but requires technical knowledge, time, and the ability to interpret raw meteorological data.

Option 2: The Easy Way (HailScore)

Go to myhailscore.com

Type your address

Get your HailScore (0 to 100) instantly

View your storm timeline, map, and full report

HailScore handles the geocoding, data querying, proximity analysis, severity weighting, and visualization automatically. The 4.5 million radar records across all 50 states are already indexed and ready to search. What would take hours of manual data wrangling takes HailScore about 10 seconds.

Real-World Applications of NOAA Hail Data

Home Insurance Claims

The most common application. When you file a hail damage claim, having NOAA-backed data from HailScore strengthens your position. You can provide your insurer with specific dates, estimated hail sizes, and proximity to your address. This is the same data their own adjuster will pull.

Home Buying and Selling

Smart homebuyers check the hail history of a property before purchasing, just like they check flood zones and crime statistics. A property with a high HailScore may have hidden roof damage that the seller has not disclosed. Conversely, a low HailScore provides confidence in the roof's integrity.

Roofing Contractor Verification

When a roofing contractor tells you that you need a new roof due to hail damage, you can verify their claim with HailScore. If your HailScore is low and your area shows minimal hail activity, you have reason to question the recommendation.

Roof Maintenance Planning

Even without an active claim, knowing your cumulative hail exposure helps you plan for roof replacement. A roof that has weathered five significant hail events over 10 years may need replacement sooner than its manufacturer's warranty suggests.

Legal Disputes

In cases where insurance claims are denied or disputed, NOAA radar data serves as objective evidence. Courts and arbitrators widely accept NEXRAD data as reliable evidence of weather conditions at specific times and locations.

The Future of Hail Data

The technology behind hail detection continues to improve:

Phased-array radar is being tested as a potential NEXRAD replacement. These systems can scan the full atmosphere in about one minute instead of five, providing more frequent and detailed hail detections.

Machine learning algorithms are being applied to radar data to improve hail size estimation and reduce false positives.

Satellite-based hail detection is emerging as a supplemental data source, potentially filling gaps in radar coverage.

Higher-resolution data from upgraded radar systems may eventually enable rooftop-level hail analysis rather than neighborhood-level estimates.

As these technologies mature, tools like HailScore will become even more precise and valuable for homeowners.

Frequently Asked Questions

What is NOAA hail data?

NOAA hail data refers to hail detections recorded by the NEXRAD radar network and archived in databases like the Severe Weather Data Inventory (SWDI). This data includes the date, time, location, and estimated size of hail detected by radar stations across all 50 states.

How do I look up hail history for my address?

The easiest way is to use HailScore. Enter any US address and get an instant hail exposure score (0 to 100) based on 4.5 million NOAA radar records. The report includes a timeline of specific hail events near your property with dates, sizes, and distances. You can also query NOAA's SWDI database directly, but this requires technical knowledge and does not provide address-level analysis.

Is NOAA hail data reliable?

Yes. NEXRAD radar data is the primary source used by the National Weather Service, emergency management agencies, insurance companies, and forensic meteorologists. It is the gold standard for verifying hail activity in the United States. While radar has limitations (it detects hail aloft, not necessarily on the ground), it is the most comprehensive and reliable data source available.

Do insurance companies use NOAA data?

Absolutely. When you file a hail damage insurance claim, your insurer or their third-party vendor will pull NOAA radar data to verify whether hail was detected near your property on the reported date. This is standard practice across the insurance industry. HailScore gives homeowners access to the same data, leveling the playing field.

What size hail does NOAA detect?

NEXRAD radar can detect hail of virtually any size, but the automated algorithms in the SWDI database typically flag hail estimated at 0.75 inches (about penny size) and larger. HailScore's database of 4.5 million records uses this same 0.75-inch threshold to focus on hail large enough to potentially cause property damage.

How far back does NOAA hail data go?

The SWDI archive contains hail data going back over 20 years. HailScore analyzes approximately the last 10 years of data, which provides a comprehensive view of your property's hail exposure while focusing on the time period most relevant to current roof condition.

Can I access NOAA hail data for free?

The raw NOAA data is publicly available through the SWDI web interface at ncei.noaa.gov/swdiws/. However, the data is in technical format (CSV/XML) and requires geographic coordinates rather than street addresses. HailScore provides the same underlying data in a homeowner-friendly format, also for free.

What is the difference between NEXRAD and SWDI?

NEXRAD is the radar network (the hardware and software that detects hail in real time). SWDI is the database that archives the detections after the fact. Think of NEXRAD as the camera and SWDI as the photo album. HailScore accesses the SWDI archive to look up historical hail events for your address.

How does HailScore use NOAA data differently than other tools?

HailScore combines NOAA radar data with 8 additional data sources (wind, solar, tree canopy, property data, and more) to create a comprehensive property risk assessment. While other tools may provide raw radar data or single-event reports, HailScore synthesizes 9 data sources into an address-specific, 0 to 100 score that any homeowner can understand. The basic report is free at myhailscore.com with no signup required.