How HailSignal works
From radar to the alert on your phone in five steps. Confidence describes the supporting evidence, separately from hail size and possible damage.
Collecting, around the clock
We process available radar data, official warnings, satellite lightning data and ground reports. Coverage explains the areas, approved sources and Swiss hail season.
Detecting suspicion C1
From the radar data we compute where hail is likely and – where the source allows – how large the stones are. Every suspicious cell is tracked over time – that yields a storm track with direction and speed. This is level C1: a substantiated suspicion. Nothing is reported yet.
Assessing radar evidence C2
Sufficient radar evidence can already support C2. A matching official hail warning or lightning jump can also raise an initial suspicion to C2. This is not yet ground evidence. Each alert states its reasoning.
Confirming on the ground C3 · C4
“Very likely” requires an observation from the ground, such as a verified official spotter report. In Germany, two independent reports from the German Weather Service’s WarnWetter app count for this; nobody checks them individually. And “confirmed” is not granted by us but by four independent users who were on site.
Alerting – and staying honest
You get the alert on your channels as soon as the evidence holds – with location, storm track, hail size and confidence level. We check every 5 minutes; there is no fixed delivery time. And if the evidence no longer supports an event, you get an all-clear. We only report what the evidence chain really holds – better one alert less than one wrong one.
The confidence ladder at a glance
| Level | Meaning | Evidence |
|---|---|---|
| C1 | possible | a single radar signal |
| C2 | likely | sufficient radar evidence, or radar suspicion with matching warning/lightning evidence |
| C3 | very likely | + ground observation (Germany: two WarnWetter app reports) |
| C4 | confirmed | + four independent users on site |