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Thunderline turns what you can see and hear into numbers you can act on. Time the gap between the flash and the thunder and it gives you the distance and a verdict based on the 30/30 rule, keeping a history of readings so you can tell whether the storm is closing or moving away.

The severity estimator works from hail size against everyday objects, wind clues and damage signs, and scores them against the real severe-weather thresholds. The storm log records date, place, storm mode, peak severity and notes.

A structure guide covers seventeen features — shelf cloud, wall cloud, gust front, mammatus, overshooting top and the rest — with what each one looks like, what it means and what to do about it, plus a safety screen and the full Beaufort scale. Offline, no account, nothing recorded leaves the device.

This is an observation aid, not a warning service. Always follow official alerts.