The complete guide to mountain thermal wind

What is all this talk about thermals lately? Why is it so important to understand thermals in Western mountains while hunting elk?

As for the first question, it is simple; the last decade or so has introduced us to podcasts, prolific hunting channels on YouTube, blog articles like this one, and social media. This has opened the flood gates of information and new terms to Western hunting and consumed the minds of hunters everywhere.

Thermals have always existed. They have been known to Western hunters since ancient times. Now, in a world more connected, the term thermals has stirred seemingly more questions than answers. Stick with me, once you finish this article you will have everything you need to know about thermals as they relate to hunting in the mountains.

Grainy phone picture, elk are circled

Why you need to understand thermals

Look closely at the above picture. I know it’s grainy, I took it with an old iPhone a few years ago. Notice how the elk are feeding at the base of a mountain. To set the stage, it’s dawn and late August.

Why are the elk here?

Elk live by thermals. They move, bed, and feed with diurnal thermal changes in the mountains. In this case, the thermals are moving downhill. The elk are strategically set up to smell anything approaching from the mountain, and see anything approaching from the large meadow. This is a key factor to their keen survival habits. As the sun begins to heat the ground, the thermals will shift upward and the elk will head up the mountain to bed down.

As an archery hunter, this particular scenario would be an impossible position. You will not call them across the meadow, and it would be nearly impossible to stalk from the mountain. They typically begin their trek upward before the thermals shift. Understanding thermals will help you develop a successful strategy a little later in the day.

Wind versus thermals

Wind and thermals are different. Kind of. I like to think of wind as a macro-thermal, while mountain thermals are micro level.

Wind is, in the simplest explanation, a result of the sun unevenly heating the earth. Variations in temperature create pressure imbalances which creates wind. Cool air is heavier than warm air. This is why heat rises. As warmer air rises, it pulls air with it creating wind. Cool air swoops in to replace the warmer air that is rising and on a very basic level, this is what wind is.

Think of your freezer. When you open the freezer door you get a blast of cold that comes out in a downward motion. Warm air is lighter, and thats why you get this sensation when the door is first opened.

Prevailing winds that you can set your watch to are no different. At a certain point during the day, the sun has warmed up a specific area enough that the air begins to rise. As a result, it pulls cooler air that is replacing the warm air moving up and out. This is why I think of wind as a macro-thermal and mountain thermals as a micro-thermal.

What are diurnal thermals in the mountains?

Mountains have very different dynamics than other terrains. Steep elevation variations, sun exposures, and temperature swings are among the reasons why.

With what we discussed about wind, think on a smaller, more micro scale. Cool, heavy morning air settles downward. Sometimes, the downward air movement is so minimal that it doesn’t even register to a hunter. They move down from a ridge at first light and by lunch are blaming the wolves for no game in the area. The reality is this; any game that was below you, smelled you and left.

Side note, I am not some defender of wolves with that comment. I purchase the maximum amount of wolf tags every year and do my best to protect our ungulate populations in Idaho.

Then, as the ground warms from sun radiation, it begins gradually warming the air. As the air warms what happens? It’s lighter than cooler air and begins to move up the slope while simultaneously pulling cooler air down. This, in the world of Western hunting, is known as swirling thermals. It is the most unstable period of air movement and it happens as the ground warms in the morning, and as it cools in the early evening.

As the sun produces more ground heat the swirling will stop. At this time, you can expect more consistent upward movement throughout the rest of the day until temperatures begin cooling in the evening.

Think of a pot of cold water that you just put on a hot stove. It does not instantly boil, it warms slowly. As it heats, you begin seeing small, inconsistent bubbling. When it reaches that magic temperature it is a nice, consistent boil. Predictable. Then you shut the heat off and it quickly stops boiling. Air on a mountain range behaves very similar.

Understanding Mountain Thermals

Basically, sun-exposed warm mountain air goes up. Cold, shaded air goes down. But, it’s not always that simple.

You must always keep in mind other factors. A storm front can totally derail normal thermal patterns. A single dark cloud can create shifts or swirling air. Dark timber can totally shift the thermals, and sometimes it won’t affect it at all.

I was once side-hilling an open face at about mid-slope. It was 10am and the thermals were predictably moving up. As I entered some darker timber, it immediately shifted to a downward thermal. As I exited the timber, it changed back to upward. However, the next copse of dark timber I entered did not change to a downward thermal. In fact, a cow moose was bedded above me about forty yards. She smelled me immediately and got up and left.

I do not have an answer as to why the thermals can be so unpredictable. There was some kind of temperature dynamic that was taking place and it had an effect on thermals. Who knows?

The best advice anyone can offer you in terms of unpredictable thermals is use your wind checker frequently. Constantly, in fact. The slightest unnoticeable shift will betray you and you will never know.

A photographic report on thermals

Okay elk slayers, now for the fun part. We are going to examine multiple photos of mountain ranges and analyze the thermal patterns. Don’t skimp on this section, study each photo and key in on the directions.

Feel free to scrutinize this data; thermals are not always as simple as up or down. Come up with your own scenarios in these images that may differ from my analysis. Ask questions, take notes, and share this information.

Image 1
Thermal air movement.


During the summer, there is almost always elk hanging in the bottom of this drainage. Sometimes it’s only a cow elk, sometimes it’s several elk. I am usually camped not far from here, and I know the area well.

It’s easy to see why. Elk have protection and visibility towards the river, and scent protection from the slopes. They also have a quick escape route, they always run up the drainage towards that sunny slope.

In this case, the shaded hillsides spend most of the morning like this due to the sun being blocked by another mountain behind me. From dawn until about 11am, thermals will essentially move down and towards the river because it takes much longer for the ground to heat up.

Remember, in the mountains, it is the warming ground that heats the air. Not the sun directly heating the air. This mainly applies to early morning hours. Behind the shaded hillsides, the sun bathing slope has upward moving thermals. The sun has heated the ground on the sunny slope much sooner and quicker than the shaded area.

Image 2
Basic thermal concept

Image 2 highlights a basic mountain thermal concept. Direct sunlight is warming the ground/air much faster than the shaded slope. Thus, storm fronts and other factors aside, this is going to be the predictable thermal pattern.

Most likely, later in the afternoon or early evening, the sun exposure will be opposite of this morning image. The area you currently see exposed to the sun will be shaded, and the shaded hillside will have sun. This would effectively flip both arrow directions.

Image 3
Yellow arrows: dawn
Red arrows: about 8:30am

Love this image. Let’s analyze the morning thermals from this ridge at two different times.

The yellow arrows signify first light/dawn. Red signify two or three hours later. Notice that sunlight does NOT necessarily mean upward thermals. At dawn or first light, the sun has not generated enough heat to impact the thermals, so they are going downward. After a few hours, they switch in the left-side arrows. The ground has warmed.

However, notice the direction on the right-side arrows. They remain in a downward thermal. This is because the sun takes longer to reach this slope due to directional face. It could be closer to noon before this thermal switches. Another possibility would be longer swirling thermals.

Exact times for thermal shifts vary greatly from one mountain to another. Especially from state to state. I wish I could provide an accurate time chart for shifting thermals. It’s just not possible. Sun exposure, regional climate, elevation, daily weather, and obviously geographic region will factor thermal shift times.

In my area, you can generally expect downward thermals until close to 9am, swirling thermals for 30-60 minutes, upward thermals from 10am until about 5pm, another swirling cycle, then downward thermals to dark.

This is where I need to be careful, the above mentioned time chart is very generalized and a reference to only my local hunting regions. North Idaho will be different than Southern Arizona. The Oregon and Washington Coast will be different than the Bighorns in Wyoming. However, this rule of thumb will play out within a reasonable range of time throughout the American West.

Image 4
Mountain thermals mid-day

Getting a little more in-depth in this photo. I want to provide a few points about mid-day and various seasons.

Mid-day hunting in September will have different thermal patterns than say, November. It is completely plausible to see the above thermal patterns at 1pm later in the season. Cooler fall temperatures are setting in. The directional sun exposure begins to shift. Some parts of the mountain may not have direct sun exposure all day long. With cooler fall temperatures, thermals can quite easily remain in a downward pattern from dawn to dusk.

Notice in this image the varying thermals. Crossing one drainage slope to the other side can completely shift thermals to up or down. This can happen any time of the year, not just late season hunting.

Importantly, the up-down arrows referenced “cloud shade” can be tricky. A fast moving cloud that temporarily shades a point on the mountain will most likely not affect the thermal direction. However, a slow, lingering cloud can. Typically, what I’ve noticed is a lingering cloud will give you some swirling effects.

While walking a mountain, it is not uncommon to notice a cloud suddenly block the sun. You feel the temperature change. A few minutes later the sun shows itself again and you warm back up. No big deal. Keep in mind that below the cloud shade, the sun is still out and thermals going upward of this will most likely overpower any temporary cloud shade temperature drop.

Just monitor the lingering clouds or the very large clouds that hide the sun for long periods of time. They can and will create thermal shifts.

Image 5
Thermal variations

This image can be found on my home page, I took it during archery elk season, 2018. As a side note, there were huge cutthroats in that creek, literally visible from where I snapped this image.

Predictably, most of the arrows show an upward thermal direction throughout the drainage slopes. However, see the two lines on that North-face with opposite arrows? There were elk bedded down at about mid-slope. Sadly, all cows and they totally busted me and fled.

Once I hit that slope, there was no noticeable thermal direction. My wind checker revealed that the thermals would go up and down and seemed to changed with every step I took.

This particular day was abnormally hot. The dark timber maintained a cooler temperature. But, the heat from the ground below was sending thermals upwards towards the slope. This is not uncommon, you will find swirling thermals in these types of areas mid-day.

My goal this day was to stay mid-slope, moving horizontally where I was finding elk bedded. It was perhaps the most consistent thermals I have ever experienced but the heat created other factors that were difficult to overcome.

Concluding mountain thermals

Let’s say you live in Pennsylvania or Kansas and have been wildly successful hunting whitetails. You’re planning on heading West in pursuit of high mountain elk or mule deer.

Typically, hunters like this do their due diligence when it comes to strategy, gear, E-scouting, learning elk calls, and learning how to overcome elevation sickness.

It’s thermals that destroy hopes and dreams. Even amongst experienced Western hunters, thermals and a lack of understanding basic thermal dynamics will quickly and quietly send your targets packing. Sometimes miles away.

If you have stuck with me throughout this article, you can rest assure that you are better equipped than a large portion of other hunters on the mountain. It’s a huge advantage. In the West, thermals are very different than prevailing winds of the Mid-West and Eastern states.

Understanding thermals can make you deadly. The RMEF put this article out that discusses how to make the wind your friend.

Also, make sure you watch this video by Randy Newberg. He provides a visual aid in real time that show effects of not understanding thermals.

Be sure to have plenty of wind checkers and good luck this season! As always, I sure appreciate the read!

Jim Huntsman

3 thoughts on “The complete guide to mountain thermal wind

  1. Jim, thanks for this article, it is an interesting and complicated topic.

    As a hang glider pilot with 2000 hours and another 3000+ in ultralight aircraft who has flown in about 25 states I have first hand knowledge of thermals like few others. In flying circles a thermal is generally thought of as rising warm air while it is understood that cooler air fills in behind it. Therefore finding a source for rising warm air can help us envision the most likely areas of sinking air and how strong it might be.

    While I am an eastern hunter, I have hunted elk several times in the Steamboat Springs area.
    Movement of air because of the sunlight is basic but understanding what we are seeing is sometimes not. With mostly hardwood forests in the east you can actually see well formed individual thermals slide up the side of a mountain! The leaves on maples and oaks will show their undersides so the thermal is the light green area on the mountainside. This is not so obvious in the west where giant soft wood stands do not move in the same way. Also, in hardwood areas where the trees actually lose their leaves big changes occur. When snow is on the ground it is the brown tree trunks at a favorable angle to the low winter sun which will warm up and create thermals!

    One can still see thermals causing a streak of higher movement in piney forests. As you reported, early in the day thermal activity is immature and spotty and matures into larger, more consistent patterns as the day wears on. Bearing this in mind, depending on the size of the source and the maturity of the day, one can begin to understand what is happening a little better.

    Every serious hunter would benefit from reading about thermals from a pilot’s perspective. My favorite text is “Meteorology for Glider Pilots” by C. E. Wallington but nothing beats first hand experience either airborne or on the ground with your wind checker firmly in hand!

    Thanks for the article and good hunting!

    Like

    1. Thanks Chas!

      I completely agree about getting thermal perspective from a pilot. If ever you want to collaborate on a more in depth piece about thermals, let me know!

      Like

      1. Sure!
        Let me know when and I will gladly pitch in.

        Like

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