Lightning 30-30 Rule Countdown
NWS 30-30 rule: seconds between flash and thunder -> distance in miles and seek-shelter advisory.
Example
You enter
- Flash to bang (s) 15
You get
- Distance miles 3
- Distance (km) 4.828
- Seek shelter Yes
Details, formula, and sources
Sound speed ~1125 ft/s.
distance_mi = flash_to_bang_seconds / 5 (sound at sea level ~ 1125 ft/s). 30-30 rule: under 30 s flash-to-bang (~6 mi) -> seek shelter.
NOAA / NWS lightning safety; 30-30 rule is a public guideline.
weather.gov/safety/lightning.
Geometry is not forecasting. Avalanche advisory and incident commander govern.
Field names used by the API: flash_to_bang_s, distance_miles, distance_km, seek_shelter
- Sound speed ~1125 ft/s at sea level; 5 s ~ 1 mistandard atmospheric model
- 30-30 rule threshold 30 s flash-to-bang (~6 mi); resume after 30 min of last detected strikeNWS public guideline