Knowing that hail hit a county is useful. Knowing exactly which streets took a direct hit from a 2.5-inch stone — and which ones were on the edge of the swath — is the difference between a productive canvass and a wasted afternoon.
THOR Storm Mapper's new Hail Swaths feature maps radar-derived hail paths directly on your impact map as concentric, color-coded bullseye overlays. Every storm cell that produced measurable hail gets its own set of rings, graded by hail size from the outer edge of the swath to the hot core where the largest stones fell. This post explains what hail swaths are, where the data comes from, and how to use them in the field.
What Is a Hail Swath?
A hail swath is the ground-level path traced by a storm cell as it moves across the landscape, dropping hail along the way. Because storm cells travel — typically northeast at 20 to 50 mph — the hail they produce doesn't fall in a single spot. It falls in an elongated corridor that can stretch for dozens of miles. The width and intensity of that corridor depend on the storm's structure, the size of the hail core, and how long the cell maintained its intensity.
Traditional hail maps show you a point — the centroid of a reported hail event. A hail swath shows you the full path: where the storm entered, where it peaked, and where it exited. For anyone working storm damage professionally, that path is where the money is.
Where Does the Data Come From?
THOR's hail swath data is sourced from official government radar archives and processed through our proprietary pipeline. Every swath you see on the map is built from radar-observed hail data — not modeled estimates, not third-party interpolations. The underlying source is the same radar network that powers every major weather service in the country.
Our system reconstructs the full path of each storm cell across the scan period and renders it as a set of concentric threshold rings directly on your map. The processing that turns raw radar returns into clean, accurate bullseye overlays is proprietary to THOR.
How to Read the Bullseye Rings
Each storm cell's swath is rendered as a set of concentric rings, with the outermost ring representing the minimum detectable hail size and the innermost ring representing the largest stones the radar detected. The color scale is consistent across all swaths on the map:
| Ring Color | Hail Size Threshold | What It Means |
|---|---|---|
| Blue | ≥ ½ inch | Marginal hail — cosmetic damage possible on older roofs |
| Green | ≥ 1 inch | Quarter-size — functional damage threshold for most insurance carriers |
| Lime | ≥ 1½ inches | Ping-pong ball size — high probability of functional damage |
| Amber | ≥ 2 inches | Egg-size — near-certain functional damage on any roof age |
| Red | ≥ 2½ inches | Baseball-size — catastrophic damage, structural risk |
| Purple | ≥ 3 inches | Softball-size and above — extreme event |
The innermost ring on any given swath tells you the peak hail size the radar detected for that cell. If you see a purple core surrounded by amber and red rings, you are looking at a cell that produced softball-size hail at its peak, with baseball-size and egg-size hail extending outward from the core path.
How to Enable Hail Swaths in THOR
Hail swaths are tied to the Timeline Playback feature. Here's how to access them:
- Run a scan for your target date range using the Detection Controls panel.
- Once the scan completes, open the Timeline by tapping the TIMELINE chip in the layer bar.
- With the Timeline open, tap the SWATHS chip — it will appear in the Timeline bar alongside RADAR.
- Drag the scrubber to a specific date or storm event. The swaths for that time window will render on the map.
- Use SHOW ALL on the Timeline to display all swaths across the full scan period simultaneously.
Swaths are rendered at zoom level 8 and above. At national view, the SWATHS chip will display a "ZOOM IN" prompt — zoom into your target market and the bullseye rings will appear automatically.
Practical Applications for Roofing Contractors
The most immediate use case is canvass targeting. When you pull up a hail swath for a storm that hit your market, you can see at a glance which neighborhoods sat inside the amber or red rings versus which ones were on the blue fringe. Your crew's time is finite — start in the core, not the edge.
The second application is claim documentation. When a homeowner's adjuster pushes back on the size of the hail that hit their property, you can pull up the THOR swath for that storm and show exactly where the property sits relative to the radar-detected hail core. This is not a third-party estimate — it is NOAA radar data, the same source the insurance industry uses for its own storm verification.
The third application is competitive positioning. If you can identify which storm cells produced the largest hail and trace their exact paths, you can be in those neighborhoods before the competition has finished looking at a county-level hail report. The swath tells you the street-level story; the county report tells you the headline.
How Swaths Interact With the Timeline
Because hail swaths are tied to the Timeline scrubber, you can use them to reconstruct a storm event in sequence. Drag the scrubber forward through a storm day and watch the swaths appear as each cell's radar returns are logged. This is particularly useful for multi-cell or squall-line events where several storm cells tracked across the same market in succession — each cell gets its own swath, and you can see the order in which they moved through.
Combined with the Radar Overlay, this gives you a complete picture of the event: the radar shows you the storm structure at each moment, and the swaths show you the cumulative hail footprint each cell left behind.
A Note on Data Coverage and Timing
Swath data is typically available within a few hours of a storm event. For historical scans, coverage extends back up to two years and is available for any event where the radar detected a hail-producing cell. Coverage is nationwide across the contiguous United States.
THOR pre-warms the swath cache nightly for recent events, so for storms in the last 30 days, swath data loads quickly. For older events, the first load may take a few seconds as the data is prepared.
The Bottom Line
Hail swaths turn a point on a map into a path on a map. They show you not just that hail fell, but where it fell hardest, how far the damage corridor extends, and exactly which properties sat inside the core versus the fringe. For anyone whose livelihood depends on being in the right neighborhood after a storm, that is not a nice-to-have. It is the whole game.
Hail Swaths are available now on all THOR Storm Mapper subscription plans. Open your Timeline, tap SWATHS, and see the storm the way the radar saw it.