Image of the November 2023 Wilderness Magazine Cover Read more from the
November 2023 Issue
Home / Articles / Trail life

A short little guide to thunderstorms

How does lightning work?

85-90% of lightning stays in the clouds, aka sheet lightning.

The sky: Positive charges up high, negative charges down low, convection in storm clouds split positive and negative charges, negative charge step leader towards…

The land: Positive charge upward leader, visible return stroke…

When leaders meet the air heads +24,000°C, expands and contracts, then BOOM makes thunder!

What is…

Side flash? Lightning jumps from a poor conductor to an easier path (us!). Can arc up to 15m!

Ground current? Lightning dissipating in the ground. Difference in voltage drives current through us. Smaller the difference = less damage. Cables, ropes, streams, wet roots & rock, all spread current

  • A – feet wide, bad
  • B – feet together, better
  • C – livestock, high risk

Lightning position? Assume in 30/30 rule:

  • Protecting ears
  • Feet touching allows current a short path in/out
  • If sleeping, stay fully on your mat, don’t touch tent poles.

30/30 rule

When flash to crash is <30 seconds, the storm is <10km away. Time for immediate action! Spread groups out, assume lightning position. Wait 30mins from last crash before continuing.

Warning signs

Sudden burst of rain or hail

Fast moving cold front

Metal buzzing or glowing blue aka Saint Elmo’s Fire*

Hair standing on end or cracking*

*immediate high danger

When to take action?

Make route choices before/in case of a storm.

  • Even height forest
  • Gulleys !
  • Ridgelines !
  • Water
  • Sparse trees
  • Open area
  • Caves and overhangs (lightning can jump the opening & run on water inside)
  • Peaks ✗✗✗