Thunderstorm Risk Assessment
Lightning kills hikers on exposed ridges every summer. Pick the month, time of day, your terrain and the weather trend to estimate your thunderstorm risk and get the right response.
Assess your storm risk
A simple rule-based screen — not a forecast. Always combine it with a live NWS / local-weather alert. Try the example first.
Results
How is this assessed?
There is no single closed-form equation — this is a rule-based risk screen. Each factor contributes points: season (summer +3, spring/autumn +1, winter +0), time of day (afternoon +2, evening +1, morning/night +0), terrain (exposed ridge +2, open valley/canyon +1, forested +0), and weather trend (approaching storm +3, building instability +2, steady +0, clearing −1). The total score maps to low (≤2), moderate (3–5) or high (≥6) risk.
30/30 rule: if the time between seeing lightning and hearing thunder is 30 seconds or less, the storm is within about 10 km and you should take shelter immediately. Wait 30 minutes after the last thunder before leaving shelter.
Sources: U.S. National Weather Service (NWS) lightning safety, 30/30 rule; Leave No Trace / AMS mountain-weather guidance. This is an educational screen only — always follow official warnings and local conditions.