Anyone who spends time hiking regularly in North America’s mountain ranges during the summer will encounter thunderstorms at some point or another.
This article will teach you the basics of thunderstorm characteristics in the mountains while providing you with actionable advice for lightning safety while hiking or climbing, or any other activity that involves recreating in the mountains.
Lightning is one of the most unpredictable hazards to backcountry travel in the mountains, but with proper planning and evaluation, the risk of being struck by lightning can be mitigated.
Even though I’m a trained meteorologist, I’ve had plenty of close calls with thunderstorms up high in the mountains — mostly before but even after earning a degree in meteorology!
Lightning an inherent risk — even if a small one — anytime you recreate outside during thunderstorm season. Even with best intentions, sometimes you end up in the wrong place at the wrong time.
The goal of this article is to help you improve your knowledge, evaluation skills, and decision-making with regard to thunderstorms and lightning, in order to lessen your chances of getting caught in a scary lightning situation.
Thunderstorm Meteorology 101
I’m not going to dive too deep into the meteorology of thunderstorms, but it helps to have a basic understanding of what causes thunderstorms to occur as a hiker or outdoors enthusiast, as well as the regions that are more prone to thunderstorms.
While each region of the country has its own unique climate, it should be known that every mountain range in North America experiences thunderstorms.
The most active mountain regions for thunderstorms in the summer are in Colorado, New Mexico, Arizona, and Southern Utah while the least active regions are in the Cascades of Oregon and Washington — and if we’re including the far north, then also Alaska.
Here is a quick regional overview.
Spring and summer thunderstorms are most common in the Southern Appalachians — i.e. the Carolinas, Georgia, and Tennessee, while thunderstorms gradually become less frequent the farther north you go up into New England.
Summer weather patterns in the Southern Appalachians alternate between stretches of hot, dry weather and wetter conditions with afternoon storms happening daily. Remember, North Carolina contains the highest peaks in the Appalachians and can be very exposed to lightning despite plenty of tree cover.
Storms are less frequent in the Northern Appalachians and in New England, but they absolutely happen. The White Mountains and similar ranges above treeline are particularly dangerous areas to get caught in a storm. Organized systems that move across this area in the summer can occasionally produce strong to severe thunderstorms.
The Rockies are the most well-known region amongst hikers and climbers for thunderstorm exposure and lightning risk — due to the sheer height and prominence of the peaks and the large expanses of exposed terrain above treeline.
The North American Monsoon pattern impacts the Southern Rockies every summer in July and August. Essentially, this is a seasonal circulation of subtropical moisture that originates in Mexico and shifts northward into the Four Corners region every summer.
When this moisture encounters the elevated terrain across the Four Corners states, the result is periods of near-daily thunderstorms across the mountain regions of Colorado, New Mexico, Arizona, and Southern Utah.
The higher peaks including the “Fourteeners” of Colorado are especially vulnerable during monsoonal patterns since the height and vertical rise of the mountains aids in thunderstorm development, and much of the terrain in Colorado is above treeline. Within Colorado, the San Juan Mountains experience the most frequent thunderstorms.
Farther north — thunderstorms are still quite common in the mountains of Wyoming, Idaho, Montana, and Alberta, especially near the Continental Divide. Storms are just not quite as frequent here compared to Colorado. Many of the thunderstorms that occur in the Northern Rockies are not related to the monsoon.
However, on occasion monsoonal moisture surges northward into the Northern Rockies, and when this happens areas such as the Wind Rivers and Tetons can get into daily thunderstorm patterns. The Grand Teton has been the site of multiple lightning accidents in the past due to its exposure.
The Sierra Nevada, Cascade, and Coastal Mountains
The West Coast mountain ranges experience fewer thunderstorms compared to the Rockies. This is especially true in the Cascades and Coast Ranges in Oregon, Washington, and British Columbia due to the cooler waters of the Pacific Ocean.
Thunderstorms can and do occur here, so don’t let your guard down, but it typically takes an organized system for it to happen in these areas. Farther east in each of these states/provinces across the more interior ranges (such as the Wallowas in Oregon), thunderstorms are more common but still less frequent than in the Rockies.
Farther south, the Sierra’s in California can experience prolonged dry and sunny stretches of weather, but the monsoon circulation sometimes shifts farther west and when this happens, thunderstorms become very common along the Sierra Nevada crest in particular.
During these patterns, often the storms are very slow-moving and hang out over the higher peaks for long periods of time.
Similar to Colorado, the Sierra’s feature significant expanses of above-treeline terrain that are more vulnerable to lightning danger.
Here is a good map that shows the average number of thunderstorm days across the U.S. for a good general idea of thunderstorm climates.
Thunderstorms – 3 Key Ingredients
To put it simply, there are three main ingredients needed for thunderstorms to develop: moisture, instability, and lift.
There has to be some source of moisture present for cumulus clouds to form and develop into thunderstorms. Oceans, seasonal circulations (such as the North American Monsoon), and soil/vegetation are the main sources of moisture that fuel thunderstorms.
The warmer the ocean temperature, the more moisture is available — this is why moisture that originates from the Gulf of Mexico supports stronger thunderstorms compared to moisture that originates from the Pacific Ocean off the U.S. and Canadian Coast.
The North American Monsoon becomes its own circulation as the summer progresses, but has origins from the both the Gulf of Mexico and the South Pacific Ocean (which is warmer than the Pacific Ocean along the west coast of the U.S.).
Here is a diagram showing common moisture sources that contribute to thunderstorm development.
The air becomes unstable when there is warm, moist air near the surface and cold, dry air aloft — the difference in temperature with height leads to differences in pressure and density. The warm air that originates near the surface is less dense than the colder air above, and as a result, is able to rise high into the atmosphere.
A warm, moist air parcel will continue to rise on its own, eventually cooling and condensing into towering cumulonimbus clouds that develop into thunderstorms.
The greater the temperature difference between the warm air originating at the surface and the colder air aloft, the more unstable the atmosphere is and the more likely thunderstorms are to develop.
Sunshine that heats the surface early in the day during the summer often allows the atmosphere to destabilize more quickly, especially if there is an abundance of moisture present.
You can think of moisture and instability as the prerequisites for thunderstorms, whereas lifting sources are the driver of thunderstorm development and behavior.
In a flat area away from mountains, sometimes the presence of moisture and instability that originate from daytime heating alone are enough to generate pop-up “airmass” thunderstorms.
However, in the mountains, the rise in terrain causes warm, moist air to accelerate upward at a greater rate compared to flatter area. This is a primary driver of fast thunderstorm development over higher mountain ranges, and earlier in the day than in surrounding non-mountain areas.
This is known as upslope flow — or the orographic effect — and often south-facing slopes that heat up faster in the mornings generate localized winds that flow up a mountain range, which further supports lifting. This is common across the Rockies in particular.
There are many other sources of lift that influence thunderstorms in the mountains as well. Any temperature and moisture boundaries (i.e. fronts or boundaries that separate warm/moist air from cooler/drier air) promote thunderstorm development due to the difference in air densities.
The Continental Divide in the Western U.S. is especially vulnerable to thunderstorm development, due to both the terrain uplift and the fact that the Divide often separates warmer/wetter airmasses from cooler/drier air. Often times, moisture from the Gulf of Mexico flows across the mountain-less plains and reaches the eastern slopes of the Continental Divide.
Cold fronts are also a big driver of thunderstorm development, as are upper atmospheric low-pressure troughs. These upper level “kinks” in the atmosphere often cause thunderstorms to develop in the overnight or morning hours, which can catch hikers and climbers off guard.
Managing your thunderstorm risk while hiking starts with planning ahead and gathering as much forecast information as possible.
By assessing thunderstorm potential before your hike, you can make informed decisions such as what time to start your hike, where on your hike you should make go-no-go decisions (such as at treeline or near a mountain pass), and whether or not you should choose a Plan B if the forecast looks particularly worrisome.
The hiking and climbing community uses the “be off the summit by noon” rule of thumb for summit hikes or high elevation hikes. This advice is well-intentioned and sometimes works out well for avoiding afternoon storms, but often it is too generalized.
Many lightning accidents involving peak baggers in the Western U.S. have occurred when thunderstorms popped up before noon and caught people by surprise.
Terrain, difficulty level, and exposure of your hike or climb play a big factor in timing your trip as well, and supersede a generic “be off the top by noon” mantra.
Here are some planning resources and planning advice to evaluate thunderstorm potential before your hike.
These are meant to be quick looks at weather forecasts from reliable sources, rather than teaching you to make your own forecast using satellite data, weather charts, and weather models — that would be a big subject in of itself! (But one I may offer as a course in the future).
National Weather Service Point Forecasts
The National Weather Service is the quickest and most reliable resource to check your thunderstorm potential as far out as 7 days.
The great thing about the NWS forecasts is that you can generate point forecasts for 2.5 km grid cells, meaning you can get a forecast that takes into account elevation and terrain very close to where you’re hiking.
At the time of this writing, there isn’t much thunderstorm activity going on in the Western U.S., so lets take a look at Mt. Mitchell, North Carolina as an example.
Let’s say you are planning to hike to the top of Mt. Mitchell, which is the highest peak in the Appalachian Range and a great hike as well!
First, visit weather.gov and then you can either type in the closest town where you’ll be hiking, or you can try typing in the landmark (such as a mountain or lake) to see if it will pop up in the search box.
In this example, Mt. Mitchell is a well-known landmark and shows up in the search box, which makes your work easier.
In some cases, you’ll need to enter a town or other close landmark and then use the map on the bottom right-hand corner of the forecast page to find where you’ll be hiking.
Each time you click on a point, a new forecast will be generated, and just below the map, it will show you the elevation and lat-long.
So you can poke around until you get an elevation that closely resembles where you’ll be hiking. Don’t worry if the grid location isn’t exact, as long as you are in the ballpark you will get a good idea.
Let’s revisit the original forecast. You’ll notice below that there are thunderstorms in the forecast for Mt. Mitchell every day over the next several days.
For some reason, the NWS will often say “chance of showers” or “showers likely” on its forecast graphics at the top even if thunderstorms are also expected. Be sure to read the text forecasts below, which often specify if thunderstorms are in the forecast as well.
Using this initial assessment, we know there is a good chance of rain every day and at least some potential for lightning.
Taking it a step farther, click on the link for “Hourly Weather Forecast” (shown in the image above) to get an hour-by-hour snapshot of rain and lightning potential.
Looking at this hourly forecast for “Sat May 23, 2020”, it’s obvious that rain showers will be possible at any time of day, but it doesn’t look like an all-day rain-out either.
As for lightning, the best chance is from noon-8pm, but it couldn’t be ruled out as early as 11 am. Given this information and the fact that Mt. Mitchell is a relatively exposed highpoint despite heavy tree cover, I would plan to summit early and be heading back down by no later than 10 a.m.
(Caveat: there are state park buildings you can take shelter in at the top of Mt. Mitchell, but let’s pretend like there aren’t).
Now let’s pretend that this is the lightning forecast for Longs Peak in Colorado on a day in mid-July. The upper portion of this mountain is very exposed and features lots of slow-paced Class 3 scrambling over rocky terrain. As a result, I would plan to be off of the summit no later than 9 am following an “alpine start”.
Unfortunately, the National Weather Service does not have a mobile app, so the best planning using this resource is done on a computer.
OpenSummit Weather App
OpenSummit is quickly ascending my list as one of the top resources for hikers and climbers to use for weather. This app is geared toward peakbaggers and provides weather forecasts for peaks all across the U.S. that are commonly hiked or climbed.
I like the style of the forecasts and find them to be more user-friendly and easier to read than the National Weather Service site. These forecasts are often generated from the same data as the NWS, but they are pinpointed with even greater detail to mountain summits.
Here is an example of the forecast for Mt. Mitchell, during the same time as above.
Forecasts for up to two days out are free, but in order to receive 5-day forecasts, you must sign up for the premium version which costs a very reasonable $20/year and also gets you access to powder forecasts for ski areas in the winter.
The main limiting factor of this app is that your hike simply may not be on there yet, especially if you aren’t hiking to a mountain summit. However, they are expanding their available forecast areas every year.
Overall, I highly recommend this app, and if your hike is not available, then use the National Weather Service website.
National Weather Service Forecast Discussions
I also think that it’s worth reading the forecast discussions issued twice daily by National Weather Service meteorologists for their specific regions. You can find your specific region by checking out this clickable map below.
Most states have 2-3 forecast offices, and often it is valuable to read multiple ones from around the region.
For example, if you are hiking in the Front Range of Colorado, then reading the Denver NWS discussions and the Grand Junction NWS discussions are both valuable as they offer different perspectives.
If you’re hiking in Grand Teton National Park, then you would want to check out the Pocatello and Riverton forecast discussions. As another example, if you were hiking in Glacier National park, it would be valuable to read both the Missoula and the Great Falls discussions.
Some of the language in the forecast discussions can get a bit technical (intended for other meteorologists), but hikers and climbers can often pick up valuable tidbits from quickly scanning these discussions.
Take the below discussion from the Missoula weather office as an example.
Taking a look at the second paragraph which mentions the next day’s weather, their wording would catch my attention if I was planning to hike in Glacier National Park, which is located along the Continental Divide, or any of the mountain ranges near Bozeman, Montana.
When these discussions mention tidbits such as “a few strong [storms] possible” then you should be on alert for something more than run-of-the-mill isolated afternoon thunderstorms.
Pre-Trip Terrain Assessment
Will you be ascending any summits or obvious high-points?
Will your hike be traveling above treeline, and if so, for how long?
Will you be walking on ridgelines for extended distances?
Will you be crossing multiple mountain passes?
How open and exposed is the terrain you will be hiking in?
Are you planning a multi-day backpacking trip, and if so, how can you plan your days to minimize high elevation exposure during the afternoons?
These are a few questions to consider before hiking. It helps to think about how long it will take to bail to a safer area in the event that a thunderstorm pops up during your hike.
Evaluating the Skies During Your Hike
Once you hit the trail, it’s important to pay attention to the skies and the air around you for any changes that could signal a shift in the weather. This is especially important if you know there is thunderstorm potential that day, but even if there isn’t, you want to remain aware.
Occasionally, dry forecasts prove to be wrong and you never want to let your pre-trip assessment override your instincts about what you are seeing first-hand while in the mountains.
Here are things you need to watch for while hiking.
Evaluate the skies at the start of your hike in the morning
While storms are more common in the afternoon, the early morning skies can offer some clues about what to expect later.
Clear, sunny skies
If the morning dawns clear and sunny, then your hike is off to a good start as you aren’t dealing with any surprise early morning thunderstorms.
However, as the sun hits the surface and heats up the atmosphere, this allows the atmosphere to destabilize provided there is some moisture to work with, so you’ll want to look for puffy cumulus clouds as the day progresses.
Flat, overcast skies
While a layer of flat cloud cover in the morning might seem like an ominous sign, this can actually have the opposite effect, at least temporarily.
Flat cloud layers that lead to overcast skies tend to suppress thunderstorm development, since they prevent the sunshine and heating that fuels thunderstorms to reach the surface. It usually takes a significant organized system (more likely in the spring or fall) to produce thunderstorms in such an environment.
If you are hiking under a layer of these flat clouds on a summer day without any strong weather systems or fronts expected, then it will buy you extra time as long as the clouds hold and the sun doesn’t provide much surface heating.
If and when the clouds break and the sun comes out, then take notice as the added heading could fuel storm development in the coming hours — possibly quickly if there is a lot of moisture available.
If you ever see a cluster of high, thin, slightly puffy clouds like in the image below, then take this as a sign to be on guard. These are known as altocumulus clouds and are typically a precursor to early afternoon thunderstorms.
When you see these clouds in the morning, it indicates there is already some instability aloft in the atmosphere and that it won’t take as much heating from the sun for thunderstorms to develop.
When I’ve seen these clouds on mornings while hiking in the Rockies, thunderstorms sometimes end up developing by midday or even late morning.
Dark clouds with vertical growth
If you see ominous looking clouds early in the morning that are puffy and growing vertically, rather than flat and overcast, then you may have some morning thundershowers to deal with. It does happen sometimes.
Look and feel for moisture cues
If you are hiking on a summer morning through grass, shrubs, and vegetation that are soaking wet from the previous day or night’s rainfall, then expect a greater threat for afternoon thunderstorms.
The high surface moisture you are noticing will evaporate into the atmosphere as the day heats up, and become a source of fuel to support thunderstorm development.
Another moisture cue you should be aware of is the “feel” of humidity. If the atmosphere feels more humid than usual for the climate you are hiking in, then this is a sign that there is an abundance of moisture present that in combination with heating from the sun will help to support thunderstorm development.
Look for the first small puffy cumulus clouds
While you’re hiking, keep checking the sky for those first white, puffy cumulus clouds to develop. This is not something to be concerned about in the near term, but it’s the first sign that moist air parcels are beginning to rise and thunderstorms could start to develop in the next couple of hours.
Take note of these initial clouds and where you are on your hike in relation to your objective, and start paying closer attention to the sky from this point forward.
Sometimes these clouds change little over time and will not show any growth until later in the day if at all, whereas other times they can progress from initial development into towering cumulus clouds rather quickly. If the latter happens, then your guard needs to be up.
Towering cumulonimbus clouds with dark bases
As you scan the skies during your hike, you’ll really want to start paying attention and re-assessing things as towering, puffy clouds that grow vertically and resemble cauliflowers emerge.
Clouds such as these that grow tall, grow fast, and develop dark bases are signs that thunderstorms could be developing, and it can happen fast in the mountains. You’ll also want to pay attention as to what direction the clouds are moving in, in relation to where you are.
Are the clouds moving toward you, away from you, or are they developing and staying in place right over a mountain range?
If you are on an exposed route that involves more than a quick descent to safer territory, then start thinking about whether or not to bail.
If you see a flat layer develop at the top of the clouds that starts to expand outward in a mushroom shape, then that means the developing thunderstorm is reaching its mature state and lightning is imminent.
You may not see this feature if it is developing on top of you (which is often the case in the mountains), so look for darkening and lowering cloud bases as well.
Even if you haven’t seen lightning or heard thunder yet, if you see these dark, towering clouds moving your way or developing on top of you, then it’s time to head to safer ground. Remember, the first bolt of lightning could strike where you are. Also, thunder and lightning can be obscured by surrounding mountains and terrain barriers.
Pay attention to wind shifts
When clouds are starting to threaten, you should pay attention to any changes in wind speed or direction.
If you start to notice a warm breeze that is blowing TOWARD a building cumulonimbus cloud — this indicates inflow winds that contribute to the updraft of a thunderstorm — meaning the thunderstorm is developing or strengthening.
If you start to feel cooler, stronger breezes, these are downdrafts or “outflow winds” that are blowing toward you from a thunderstorm. This means one of two things:
One, it could mean that a thunderstorm is approaching and you need to head down immediately if that appears to be the case.
On the other hand, if the storm is not heading your way but you feel these cold outflow winds — the outflow winds could trigger additional thunderstorm development in your vicinity as the flow of cooler air collides with the warm/moist air in place, and/or collides with another mountain range.
When a Thunderstorm is Imminent
Once a thunderstorm is imminent, it’s time to bail and head to a safer area unless you are highly confident that the storm is not heading your way.
Pay close attention to thunder and lightning
Obviously, seeing lightning or hearing thunder are clear signs that you are in danger, especially if you are above treeline or in any other kind of exposed terrain.
If you start to hear thunder and see lightning, pay attention to the interval between each lightning strike and each thunder clap if at all possible. Count the number of seconds between a strike and a clap, and divide by 5, to get a solid estimate of how many miles away the lightning strike occurred from you.
If you calculated 5 miles or less, then you are within a reasonable range that a lightning strike could occur, so descend to safer ground immediately.
If the lightning is greater than 5 miles away, then your immediate danger is not as high, but there is still a small chance that lightning could strike outside the 5-mile radius, especially on top of a mountain. Although rare, lightning strikes have been known to occur 10-20 miles away from the center of a storm.
If you are sure that a storm is moving away from you and the closest strike/clap estimate you came up with is greater than 5 miles away, then it would be reasonable to continue hiking provided you could still quickly bail if another storm developed.
This wouldn’t eliminate the risk, but your threat would be greatly reduced if a storm beyond 5 miles is moving away from you. This is entirely up to you, though — never second guess yourself if your gut instinct tells you to play it safe and turn around. Lightning strikes are inherently unpredictable.
The most important thing to note is that you have to asses your own lightning risk and exposure threat based upon where you are located and how quickly and easily you can retreat.
Retreating to safer ground
When you decide to turn around due to lightning danger, your top priorities should be to get below any mountain summits, ridges, or exposed mountain passes.
Ideally, you should seek out valleys, ravines or any depressions in the terrain that are below treeline. And you should also avoid any lone trees or small clusters of trees amidst an otherwise open area at all costs — instead look for more densely forested areas with trees of relatively uniform size.
If you are caught above treeline and won’t be able to make it below treeline before the storm hits, then seek out basins, valleys, ravines, and areas away from peaks and saddles.
When lightning is too close and/or you start to feel static
It’s one thing when you start to see lightning and estimate the strikes to be 3-5 miles away. However, the situation becomes much scarier when the lightning strikes are within a mile of you.
Another terrifying thing to experience is the feeling of static or the sounds of buzzing or humming in the rocks, which indicate electrical charges. If you experience either of these situations, it means that an electrical charge from the cloud above is seeking out a charge to connect with from the ground.
Buzzing rocks or a feeling of static electricity are terrifying things to experience, and it means you need to head downhill as fast and safely as possible. If you have any metal attached, such as an ice ax or trekking poles, then ditch them for the time being and go back to retrieve them once it’s safe to do so.
If you are in a group, then make sure everyone spreads out so that if the unthinkable occurs and lightning strikes — only one person gets hit instead of multiple people.
In the past, the lightning crouch was recommended for situations like this, but in recent years, experts have concluded that the lightning crouch position does not really limit your exposure to lightning and that it’s best to move to safer ground instead.
After the Storm: be wary of additional storms
After a storm has passed, there are no “rules of thumb” in the mountains when it comes to whether or not you should expect more storms. It is entirely situation-dependent. Some days, one round of storms will blow through and then it clears up for the rest of the day afterward.
However, on many days in mid-summer especially, additional thunderstorms can develop after the first round. On particularly active days, storms will roll through one after another with only short breaks in between.
You have to keep watching the skies after the storm to look for cues about what’s ahead. Only resume your trek to an exposed hiking destination after a storm if you have a good visual of the sky in the distance and are confident that you have a good weather window.
Be prepared, not scared!
Like many elements that are a part of outdoor recreation, lightning is not something you be overly fearful of. Rather, the purpose of this article is to help you become more informed, more aware, and better prepared for thunderstorms so that you can avoid frightening experiences related to lightning to begin with.
There is always an inherent degree of unpredictability when it comes to thunderstorms and lightning, and the risk of a lightning strike can never be entirely eliminated when recreating outdoors, even in valleys below treeline in relatively “safe” areas. Like all things outdoors, it’s all about risk mitigation.
By reading and applying these tips, I hope you can better prepare for thunderstorms before and during your hikes while increasing your odds of successful outings!
Did you find this article helpful? Have any questions or need any further clarification about anything?
Drop a line in the comments section below, and I would be happy to answer!