More people die from lightning on Colorado 14ers than from any other weather-related cause. Most of those deaths happen between noon and 4:00 in the afternoon, when thunderstorms build over the high country in summer.
Lightning is one of the most predictable mountain hazards. The storms follow a daily pattern, and the warning signs are clear once you know what to watch for. The rule for staying safe is also simple enough to follow when you are tired and the summit looks close.
This guide explains why Colorado afternoon storms form so quickly, when to start turning around, which warning signs matter, and what to do if you get caught above treeline anyway.
How Colorado Afternoon Thunderstorms Form
In summer, Colorado mornings are usually clear and calm. By 10:00 or 11:00 in the morning, small puffy clouds start forming over the peaks, and by early afternoon those clouds have stacked into towering thunderheads. Lightning is striking the high country by 2:00 in the afternoon.
The pattern repeats almost daily from mid-June through August, and three things drive it.
Solar heating: The sun heats the ground all morning, and the high alpine surfaces of rock, tundra, and snow heat unevenly. Warm air starts rising fast.
Moisture: The North American Monsoon pulls humid air into Colorado from the south, drawing on the Gulf of California and the Gulf of Mexico, and it peaks in July and August. That moisture feeds the rising warm air.
Elevation: The high peaks sit much closer to the level where rising air condenses into storm clouds. Storms that would take hours to build over the plains form in 30 to 60 minutes over the divide.
As a result, a clear blue sky at 9:00 in the morning can turn into a thunderstorm by noon. If you spend enough time above treeline in July, you will watch that change happen.
The Turnaround Rule
The standard guidance for any 14er in summer is to summit by noon, get off the summit by 1:00 in the afternoon, and be below treeline by 2:00 in the afternoon.
In peak monsoon season (mid-July through mid-August), move that timeline earlier:
- Aim to summit by 11:00 in the morning
- Start descending no later than 11:30 in the morning
- Be below treeline by 1:00 in the afternoon
Meeting that schedule means starting your hike very early. On most 14ers, you will leave the trailhead between 4:00 and 5:00 in the morning, and many experienced hikers start at 3:00 in the morning in July to give themselves a wide buffer.
The rule applies even if the morning sky is perfectly clear. Storms in the high country build fast, and you will not always see one coming until you are above treeline with no quick way down.
If you are 500 feet from the summit at 11:45 in the morning, the right move is to turn around. The summit will still be there next month, and lightning above treeline does not negotiate.
Warning Signs to Watch For
Weather can shift faster than your forecast predicted. Watch for these signs while you climb:
Building cumulus clouds: Small white puffy clouds in the morning are normal. If those clouds start growing taller and wider before 11:00 in the morning, the storm cycle is running early, and you should turn around earlier than planned.
Anvil-shaped clouds: A cloud with a flat top spreading sideways has hit the top of the troposphere and become a mature thunderstorm. If you can see one, lightning is already happening inside it.
Distant thunder: Sound travels far in the mountains, and if you hear thunder, the storm is close enough to be a threat. The National Weather Service slogan is "When thunder roars, go indoors." Above treeline there is no indoors, so thunder means you start down now.
Static electricity: Watch for hair standing on end, a metallic taste in your mouth, a hum or buzz from your trekking poles or pack frame, or a crackling sound from rocks. Any of these signs means the air around you is highly charged and a strike nearby is likely.
Smell of ozone: A sharp, clean smell like a swimming pool or a copy machine is another sign of strong electrical activity close by.
Fast-moving shadows on the ground: If cloud shadows are racing across the alpine terrain faster than they were an hour ago, the wind aloft is picking up, and stronger wind aloft often comes before storms develop.
If you notice any of these signs, descend immediately. Skip the photos, leave your snack unfinished, and move.
What to Do If You Get Caught Above Treeline
Sometimes a storm builds faster than you can descend. The National Weather Service is blunt about this situation: there is no safe place outside in a thunderstorm. Your job is to cut your risk while you get to lower, safer terrain as fast as you can.
Keep moving down: Do not stop above treeline to wait out the storm. Moving quickly toward lower ground is the best protection you have, and every extra minute on exposed terrain keeps you at risk.
Get off the ridge or summit: Lightning tends to strike the highest point in an area, so drop off any ridge or peak and keep losing elevation.
Avoid the obvious targets: Stay away from lone trees, isolated rock outcrops, metal structures, and ridgelines. Do not shelter in cave entrances or under small rock overhangs, because current can arc across the gap.
Avoid open meadows and saddles: Wide open ground also makes you the high point. Move toward irregular rocky terrain that has many small high points instead of one big one.
Choose uniform terrain on the way down: A boulder field where the boulders are all about the same size is much safer than the top of one large boulder. A drainage gully (not a wet streambed) is safer than the surrounding ridges.
Do not count on the lightning crouch: Older guides taught hikers to squat on the balls of their feet with their heels together and their hands over their ears. The National Weather Service stopped recommending the crouch in 2008 because it does not provide meaningful protection, and stopping to crouch only keeps you exposed longer. Lying flat is no better, so spend that time moving toward safer ground.
Spread out from your group: If you are hiking with others, keep space between each person as you descend so that one strike cannot injure the whole group and the others can give first aid. CPR works on lightning strike victims, and many survive when they are treated quickly.
Keep metal away from you: Metal does not attract lightning, but it does conduct current. Stay clear of fences, poles, and other metal structures, and keep trekking poles and ice axes low instead of raising them above your head.
Once you reach safer terrain, wait 30 minutes after the last thunder before you return to exposed ground. Lightning can strike well after a storm seems to have passed, and storms often have a second cell behind the first one.
Route-Specific Timing Considerations
The window for a safe summit differs from one 14er to the next. Here are a few examples.
East-facing approaches (such as the East Ridge of Quandary Peak) warm up first in the morning. The slopes you are climbing get sun by 6:00 in the morning in summer, so storms can build over those peaks earlier in the day. Start at 4:00 in the morning on these routes.
Long approaches (such as Mount Elbert from the North Mount Elbert Trailhead) keep you on the trail longer and expose you to more of the storm window. Start very early and pace yourself to summit well before 11:00 in the morning.
Combo peaks (Grays and Torreys, Lincoln-Bross-Democrat) add to your time above treeline. Only attempt these routes on days with clear forecasts, and start between 3:00 and 4:00 in the morning.
San Juan peaks (Handies, Sunshine, Redcloud) are far from any city, and weather radar coverage there is weaker. Forecasts are less reliable, so be more conservative with your turnaround time.
How to Check the Forecast
The general weather app on your phone is not enough. Use forecasts tuned for the alpine environment:
Mountain-Forecast.com has point forecasts for individual peaks at multiple elevations. Its "Top of mountain" forecast shows conditions at the summit, which are often very different from conditions at the trailhead.
weather.gov point forecast lets you click anywhere on a map to get a National Weather Service forecast for that exact spot. Pull the forecast for the summit coordinates rather than the nearest town. The hourly precipitation chance and the forecast discussion (linked from the page) give you a better picture than a generic city forecast.
OpenSnow has a Daily Snow blog written by Colorado-based meteorologists who explain monsoon timing in plain language. The discussion often includes guidance on which days carry a higher risk of early storm development.
Check the forecast the night before and again at the trailhead in the morning. If the storms are now forecast to arrive earlier, or the chances have gone up, move your turnaround time earlier or pick a different day.
What All of This Adds Up To
Lightning is the part of 14er hiking that demands the most discipline. The pull of the summit is real, and after months of training and a long pre-dawn drive, walking past your turnaround time can feel like throwing the day away. You are not throwing anything away, though, because the mountain will wait for you and the storm will not.
Plan to summit by noon, and move that target earlier in July and August. Watch the sky as you climb, and turn around when the rule tells you to, even when the summit looks close. Get below treeline before the storms build.
If you follow that routine on every trip, you can keep hiking 14ers for the rest of your life.