Thunderstorms and Exposed Ridges: Planning to Be Down Early

In many mountain ranges in summer, the weather follows a familiar pattern: clear mornings, clouds building around midday, and thunderstorms in the afternoon. On days like that, the deadline that matters is not sunset. It is the time you want to be off the summit, off the exposed ridge and back below the tree line or in lower, sheltered ground. Lightning, sudden cold rain, hail and strong winds are all at their most dangerous on high, open ground.

This guide plans a hypothetical summit route backwards from a storm deadline, using the Hiking Time Calculator and the Daylight Turnaround Calculator, then covers what to do when the sky changes faster than the plan.

Read the forecast first

Everything starts with the forecast for the mountains, not the town in the valley. Look for the chance of thunderstorms and when they are expected, and check the land manager's current conditions and any warnings. If storms are forecast for the morning, or the forecast is uncertain on a route with long exposed sections, the safest plan is a different route or a different day. If storms are expected in the afternoon, set an off-the-ridge time well before they are due. In this example, that is 13:00.

The route

A 14 km out-and-back to a summit with 1,000 m of climb, much of it on an open ridge above the trees. The Hiking Time Calculator, at average pace:

• The climb, 7 km with 1,000 m of ascent: 3h 04m.
• The descent, 7 km with no ascent: 1h 24m, which is Naismith's flat rate only; a steep descent is usually slower.
• Round trip: 4h 28m (Tobler cross-check 3h 34m).

Using the turnaround calculator with a storm deadline

The turnaround calculator is built around sunset, but its arithmetic works for any deadline: it finds the latest time to turn back so you finish before a cut-off, allowing for a slower return. To use it for storms, enter your off-the-ridge time in the sunset box and set the buffer to zero (or keep some buffer if you want a margin before the deadline itself).

With a 06:00 start, a 13:00 deadline, no buffer, and the 4h 28m round trip:

• Turn back by: 09:06.
• Projected finish: 11:02.
• Margin before the deadline: 118 minutes.

Now the same route starting at 08:00, a common start time for people who drive to the trailhead in the morning:

• Turn back by: 10:13.
• Projected finish: 13:02.
• Margin: minus 2 minutes. The calculator flags the plan as not safe.

Two hours later at the trailhead turns a comfortable morning into a plan that has you on the ridge as the storms arrive. That is why early starts are standard practice on storm-prone mountains.

A front-loaded route needs one more check

The calculator splits the round-trip time evenly between the outward and return legs. On this route that is not true: the climb takes 3h 04m and the descent, by Naismith, much less. So check the summit arrival against the turnaround directly. With a 06:00 start, the climb puts you on top at about 09:04, two minutes before the 09:06 turnaround. That is too tight to rely on. Any slowness on the climb means turning back short of the summit, which is exactly what the turnaround is for. If you want a realistic chance of the top, start earlier, or accept in advance that the high point may be out of reach today.

The reverse also holds: once you turn, the descent is likely to be quicker than the climb, so the projected finish of 11:02 is conservative if the descent path is good, and about right if it is steep and rough.

Watch the sky, not only the clock

A forecast is a probability, and storms do not read it. Turn back immediately, whatever the clock says, if you see:

• Cumulus clouds growing tall and dark, especially towering clouds with flat, spreading tops.
• Thunder, however distant. If you can hear it, you are within range of lightning.
• Lightning in any direction.
• A sudden drop in temperature, a strong gusty wind, or rain or hail starting.
• Hair standing on end or a buzzing from metal objects: a sign of immediate danger. Move off high ground at once.

Clouds that build early in the morning are a warning that storms may come early too. Turning around at 09:00 because the sky looks wrong is a good decision, even on a day that later clears.

If you are caught out

No place outdoors is completely safe in a thunderstorm, and the best protection is not being on exposed ground when one arrives. If you are caught:

• Get off summits, ridges and other high points as quickly as you safely can. Descend into lower, more sheltered ground.
• Avoid isolated tall trees, open meadows, open water and metal such as fences and cables.
• Spread the group out so that a single strike cannot injure everyone, while staying within sight and earshot.
• Do not shelter under overhangs or in shallow caves, which can conduct ground current.
• Put on your waterproof and warm layer. Storms bring cold rain and wind, and hypothermia can follow a storm even on a warm summer day.
• Wait for the storm to pass well beyond the last thunder before returning to exposed ground.

Follow the advice of the land manager and your national weather service for the area, which may be more specific. If someone is struck by lightning, call the local emergency number at once; it is safe to touch them and give first aid, and CPR saves lives in lightning strikes.

Other things storms change

• Streams rise quickly after heavy rain, and a crossing that was easy in the morning can be dangerous by afternoon. Do not cross fast-flowing water; wait or find another way.
• Paths get slippery, so descents slow down. Allow for it.
• Visibility drops. Navigation in cloud is harder. Keep track of where you are on the map before the cloud comes in.

The storm-day checklist

1. Check the mountain forecast and the land manager's conditions; choose another route or day if storms are likely early.
2. Set an off-the-ridge deadline well before storms are expected.
3. Plan backwards: hiking time, then turnaround against the deadline, then check the summit arrival against the turnaround.
4. Start early.
5. Carry a waterproof, a warm layer, a headlamp, a map and navigation, first aid, food, water and a charged phone. Tell someone your route and return time.
6. Turn back at the turnaround time, or the moment the sky or the thunder says so.

For the general method, see how to set a turnaround time.