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The level describes supporting evidence, not hail size or an accuracy percentage. C1: initial radar suspicion. C2: sufficient radar evidence; a matching warning or lightning jump can also raise C1 to C2. C2 is not yet verified ground evidence. C3: additionally a verified public ground report. C4: four separate on-site technician confirmations of a C3 event. Every alert includes its reasoning.

The class describes hail size estimated from radar: class 2 = 20–29 mm, class 3 = 30–44 mm, class 4 = 45 mm and up. Class 1 is below 20 mm, below the hail alert threshold. This estimate does not prove hail on the ground, actual damage or a worthwhile trip. Hail size and confidence level are separate; each alert explains its supporting evidence.

A hailstorm is a living thing – and our assessment grows with the evidence. If an event is upgraded or gets stronger, you get an update. If the evidence no longer supports it, you get the all-clear: whoever headed out should also hear about the downgrade. Nothing is changed silently – every version of an event stays traceable.

From the tracked radar cells we compute the storm’s heading and speed and extrapolate the track a short way ahead. If your rule has a base location, the alert calculates the estimated arrival time (ETA) for you. Important: this is a hint assuming the track holds – not a promise. Storms can turn or fall apart.

The most frequent reasons, in this order: no notification rule is set up (no rule, no alerts). The thresholds are strict – at class 4 and C3, things get quiet. The affected country is not selected in the rule. No delivery channel is checked – then the alert only lands in the inbox. Or the subscription or trial has expired. And: it may simply not have hailed – we would rather send one alert too few than one false alarm.

Open “Getting started” and follow the guide for your device. On iPhone or iPad (iOS/iPadOS 16.4 or later), first add HailSignal to the Home Screen using Safari and open its new icon. Then allow push notifications and select “Web-Push” in your alert rules. SMS still requires a mobile number in your account and is only available when enabled.

Yes – each account supports up to 20 rules, each with its own countries, thresholds and channels, for example for different work areas. The base location in a new rule is used for distance and drive time. Choose countries or US states to define the alert area.

HailSignal is a web app – no app store needed. “Getting started” explains installation on iPhone, iPad and Android, notification permission and a test message. Afterwards, open HailSignal from its Home Screen icon.

Open the app & push guide →

From the radar data of the national weather services in Europe and North America, complemented by official warnings (MeteoAlarm), satellite lightning data (EUMETSAT, NOAA) and verified ground reports. Every alert carries its sources and licenses – you always see what a statement is based on.

The map shows events for the selected dates and filters, which can include radar indications alone. Notifications also depend on approved sources and coverage, your rule, thresholds, channels and account status. Matching class and confidence filters therefore do not reproduce an exact delivery list. The inbox shows the alerts sent to your account.

Yes. Alerts in English automatically state hail size in inches with the US comparison object (“golf ball”) – you set the alert language in your account. The interface comes in six languages; your browser remembers the choice at the top right.

Both make the alerts better for everyone. “Confirm hail” in the inbox or on the map counts as evidence from the ground – four independent accounts lift an event to the highest level, C4. The question “Was the trip worth it?” after an event is the ground truth we calibrate our thresholds against – an honest no is as valuable as a yes.