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What is the Colorado Monsoon?

What is the Colorado Monsoon and Why Does It Matter?

When summer arrives in Colorado, it brings with it a seasonal phenomenon known as the Colorado Monsoon. This regular weather pattern, characterized by increased thunderstorm activity and significant rainfall, is well known to experienced outdoor enthusiasts – it’s hard to forget your first monsoon experience. Understanding the Colorado Monsoon is essential for anyone planning hiking, camping, or climbing adventures in the Rocky Mountains during the summer months.

In this guide, I’ll share the science behind this shift in conditions, how to plan for it in advance, and what to do if you get caught in a monsoon thunderstorm.





Table of Contents

The Science Behind the Colorado Monsoon

The Colorado Monsoon, also referred to as the North American Monsoon, is a weather pattern that affects the southwestern United States, including Colorado. It typically occurs from mid-July to early September. During this time, a shift in wind patterns brings moist air from the Gulf of California and the Gulf of Mexico into the region.

Low and high pressure centers, along with the jet stream, play crucial roles in creating the North American Monsoon. During the summer months, a high-pressure center typically forms over the southwestern United States, while a low-pressure center develops over Mexico. This pressure difference drives moist air from the Gulf of California and the Gulf of Mexico northward into the southwestern U.S., including Colorado.

The jet stream, a fast-flowing river of air high in the atmosphere, also shifts northward during summer. This shift allows the moist, tropical air to penetrate further into the continent. The combination of the high and low-pressure systems, along with the jet stream’s position, creates the necessary conditions for the North American Monsoon, leading to increased thunderstorm activity and significant rainfall in the region.

Infographic Colorado Monsoon

This influx of moisture, combined with the high elevation and intense summer heat that turns mountains into large radiators, leads to the formation of major thunderstorms, particularly in the afternoon and evening throughout August.

Understanding the science behind the Colorado Monsoon can help you make better plans before and during your hiking and camping trips in the backcountry.

How the Mountains Contribute to Storm Formation

The Rocky Mountains play a crucial role in the development of these storms. As the sun rises, it heats the mountain slopes, causing the air to warm up and rise. This process, known as convection, is the key mechanism that transforms the moist air into thunderstorms.





The Process of Storm Development

  1. Morning Heating: As the day begins, sunlight heats the mountains, particularly the east-facing slopes.
  2. Rising Air: Warm air rises from the heated slopes, carrying moisture from the valleys and lower elevations.
  3. Convection Currents: The rising warm air creates convection currents, which further lift the moist air into the cooler upper atmosphere.
  4. Cloud Formation: As the moist air rises and cools, it condenses into clouds. Initially, these are harmless cumulus clouds.
  5. Storm Development: By late morning or early afternoon, these clouds grow into cumulonimbus clouds, leading to thunderstorms. The interaction between the rising air and the moisture creates the perfect conditions for thunder, lightning, and heavy rainfall.

Timing and Signs of Storm Development

Knowing when and how these storms develop is vital for outdoor safety:

  • Early Morning: Clear skies or light cloud cover. Ideal time to start activities.
  • Late Morning: Watch for the development of small cumulus clouds. If these begin to grow vertically, a storm is likely to develop.
  • Early Afternoon: Storms are most likely to form between noon and 3 PM. Plan to be off peaks and high ridges by this time.
  • Late Afternoon to Evening: Thunderstorm activity typically peaks, with heavy rainfall, lightning, and strong winds.

Practical Implications for Hiking and Climbing

Now that you know what the Colorado monsoon is, let’s dig into what it means from a hiking, camping, and climbing perspective, both before you head out and once you are outdoors in the backcountry.





Interpreting the Forecast

Before heading out, it’s crucial to check the weather forecast. During the monsoon season, pay attention to terms like “scattered thunderstorms” and “flash flood watch.” Scattered thunderstorms indicate that while not every area will see a storm, conditions are ripe for their development.

A flash flood watch means that conditions are favorable for sudden, intense rainfall that can lead to flash flooding, especially in mountainous areas. Be extra cautious along rivers and streams and in valleys, gullys, and other runoff areas which can quickly flood.

Reading the Sky and Clouds in the Field

A large cumulonimbus cloud - a major warning sign of a monsoon storm.

Understanding cloud formations can be a lifesaver. Cumulus clouds, which appear fluffy and white, are generally harmless. However, if these clouds start to grow taller and darker, forming cumulonimbus clouds, a thunderstorm is likely imminent. These storm clouds can form quickly, so if you notice this change, it’s time to take action.

If you see storm clouds on the horizon, be very careful, as similar storms may form above you with little or no warning. I have seen clouds form from nothing and develop into full storms in less than an hour.

If it’s raining, but the clouds are overcast and low-lying, the risk of thunder and lightning are significantly lower (but still not zero). Take into account the forecast and what you see.





Mountain Weather During Monsoon Season

Making Safe Plans for Monsoon Season

A little bit of extra planning and gear during monsoon season goes a long way if you get caught in the rain or a thunderstorm. Here’s my advice on how to ensure your safety during July and August in the mountains.

  1. Start Early: Begin your hike or climb early in the morning. Monsoon thunderstorms typically develop in the afternoon, so aim to be off high ridges and summits by noon.
  2. Have an Escape Plan: Always know your quickest route to lower elevation and shelter. Avoid being on exposed ridges, peaks, or in open areas during a storm.
  3. Avoid Waterways: Flash floods can occur with little warning. Avoid camping or hiking near streams and rivers during monsoon season.
  4. Pack Proper Gear: Carry a waterproof jacket, extra layers, and a hat. Ensure your backpack is waterproof or has a rain cover to protect your belongings.




What to Do in Thunderstorms

If you find yourself caught in a thunderstorm despite your plans and best attempt to start early, follow these safety tips:

  • Seek Shelter: Move to lower ground and find shelter away from tall trees, ridgelines, and open areas. A dense forest or a low valley is preferable. Your vehicle is the best, safest option. Be careful in tents which may be crushed by falling trees.

  • Stay Low: If you cannot find shelter and lightning strikes are imminent, crouch down with your feet close together to minimize contact with the ground and reduce the risk of lightning strike. Spread your group out so that if a strike occurs, not everyone is hit.

  • Wait It Out: Most thunderstorms pass within an hour. If you can find shelter, us this time to stay as dry and safe as possible.

  • Bail & Descend: If the storm is significant and you cannot find shelter, you may wish to keep moving (carefully, so you do not slip and fall) and descend to a lower spot or shelter.

What To Do in Flash Flooding

Flash floods are sudden and can occur with little warning, especially during the Colorado Monsoon season. If you find yourself in a flash flood situation, follow these safety tips to protect yourself:

  1. Move to Higher Ground: At the first sign of flooding, move to higher ground immediately. Do not wait for the water to rise.
  2. Avoid Walking Through Water: Even shallow water can be dangerous if it is moving swiftly. Just six inches of fast-moving water can knock you off your feet.
  3. Do Not Drive Through Flooded Areas: If you are driving and encounter a flooded road, turn around and find an alternate route. Just a foot of water can sweep a car away.

If You Are Trapped:

  1. Find Shelter: If you cannot escape the floodwaters, find the highest point possible and stay there until help arrives.
  2. Call for Help: Use your phone to call emergency services. If you cannot make a call, use a whistle or flashlight to signal for help.

14ers Weather Guide

Conclusion: Plan Ahead for the Colorado Monsoon

The Colorado Monsoon is a dynamic and beautiful aspect of the region’s climate, but it requires respect and preparation. By understanding the weather patterns, interpreting forecasts, and planning accordingly, hikers, campers, and climbers can safely enjoy the spectacular Colorado mountains during the summer. Stay vigilant, respect nature, and always be prepared for sudden weather changes.

Keep reading our FAQs and additional resources to learn more about the Colorado monsoon and mountain weather safety.





FAQs

Check out my answers to some of the most common questions I get asked about the Colorado Monsoon. If I haven’t addressed your question, leave a comment below and I’ll get you more information as soon as possible.

Q: What is the best time of day to start a hike during the Colorado Monsoon season?

A: The best time to start a hike during the Colorado Monsoon season is early in the morning, preferably around sunrise. Thunderstorms typically develop in the afternoon, so starting early allows you to reach your destination and begin descending before the storms start.

A: Cumulonimbus clouds are tall, towering clouds that often have a flat, anvil-shaped top. They are significant because they indicate the development of thunderstorms, which can bring heavy rain, lightning, and strong winds. If you see these clouds forming, it’s time to seek shelter.

A: If you get caught in a thunderstorm while hiking, seek shelter immediately. Move to lower ground, avoid tall trees and ridgelines, and stay away from open areas. Crouch down with your feet close together to minimize your risk of a lightning strike. Wait for the storm to pass before continuing your hike.

A: Camping near waterways during the monsoon season is dangerous because of the risk of flash floods. Sudden, intense rainfall can cause water levels to rise rapidly, leading to potentially life-threatening situations. It’s safer to camp on higher ground, at least 200 feet away from streams, rivers, and lakes.

A: To prepare for a hike during the Colorado Monsoon season, start by checking the weather forecast and plan to start early in the day. Pack a waterproof jacket, extra layers, and a hat. Ensure your backpack is waterproof or has a rain cover. Have an escape plan and know the quickest route to lower elevation and shelter.

A: Signs that a thunderstorm is developing include the rapid growth of cumulus clouds into cumulonimbus clouds, darkening skies, increasing wind speeds, and a sudden drop in temperature. If you notice these signs, it’s important to seek shelter and prepare for the storm.

A: The Rocky Mountains are prone to thunderstorms during the monsoon season because the high elevation and intense summer heat create ideal conditions for convection. As the sun heats the mountain slopes, warm air rises, carrying moisture into the upper atmosphere where it cools and condenses into thunderstorms.

Additional Resources

Check out these websites and links with more information about the Colorado Monsoon and backcountry safety for Colorado:





Alex Derr, Founder of The Next Summit

Alex Derr is an Eagle Scout, climber, and environmental policy expert located in Denver, Colorado. He created The Next Summit to help others stay safe exploring the mountains and advocate to preserve the peaks for the future. Follow him on Linkedin or Twitter or click here to contact him.





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