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 verified 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 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 a verified ground observation. Each alert states its reasoning.
Confirming on the ground C3 · C4
“Very likely” requires a verified observation from the ground, such as an official spotter report. And “confirmed” is not granted by us but by four independent technicians who were on site.
Alerting – and staying honest
You get the alert instantly, on your channels, with location, storm track, hail size and confidence level. And if the evidence no longer supports an event, you get an all-clear without delay. 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 | + verified ground observation |
| C4 | confirmed | + four technicians on site |