Understanding Thermals to Help Predict the Wind

The hunt begins, and the wind is perfect — right in your face. Then, out of nowhere, it changes and starts racing straight downhill toward a deer bedding area. You want to cuss, but find the willpower to hold it in. Instead, you sigh and realize thermals weren’t considered…again. And deer busted you…again.

Those who are serious about bowhunting whitetails and rely on getting close, should take heed of this natural occurrence. So long as the Earth keeps spinning, it’ll keep plaguing, or helping, your hunts.

Thermals Defined

By definition, a thermal is a column of air particles that rises or falls. Warmer air is less dense than cooler air, and changing temperatures cause a distinct displacement of air, effectively creating thermal wind currents. The entire process is controlled by the sun, or lack thereof. The atmosphere warms and cools, causing air to rise and fall.

When the air heats up — usually shortly after daybreak — it rises. This causes updrafts, and these can last anywhere from three to four hours, or until well after noon.

Then, there’s usually a dead period when there aren’t any thermals. They level out. Normal winds take over completely and remain in control until thermals begin to play a role again in the afternoon.

When the air starts cooling back down — usually beginning in late afternoon — it falls. This results in downdrafts, and generally spans the last 30 minutes to two hours of daylight.

While the morning and afternoon rules work most of the time, there are rare occasions where it might differ. Because of that, a better rule to follow is that when temperatures rise, thermals rise, and when temperatures fall, so do thermals. Of course, the higher the elevation and steeper the country, the more potent and predictable thermals become.

Terrain & Topography

As mentioned, higher elevations and steeper terrain can experience swifter thermals. This is most evident in the mountains and foothills. Still, it impacts properties along bluffs, bottoms, ridges, valleys, and other changes in topography, too.

Leeward ridges are especially affected by thermals. Best explained as the downwind sides of ridgelines, these experience two different wind directions. The primary wind blows across the top, and the thermals rise up from below. This sometimes creates a swirling or tunneling effect, and deer commonly use it to their advantage by traveling through it.

Winds can swirl on their own without two directions, though. Much like water, wind bounces off objects that it hits. So, if general wind or thermals carry a column of air toward a large object, such as a bluff facing, it’ll bounce back and head in the opposite direction, especially if thermals aren’t strong enough to override it.

While those who have 30 or more feet of elevation change see just how influential thermals can be, those with less than 20 feet might not experience as strong of thermals. Completely flat terrain experiences even less. That said, it still plays a part. Swamps and marshes are prime examples. These flat areas heat up and cool down throughout the day, and this pushes around air particles, albeit miniscule.

Moving bodies of water, such as rivers, creeks, and streams, also generate thermal action. These are cooler than the air temperature, and because of that, they pull air downward. This is why hunting along the edges of water can help hunters, because it serves as a secondary thermal. Just remember, these don’t usually have strong pulls, and are really only noticeable when the actual wind is light and variable. Water thermals are no match for morning and evening thermals, either.

Regardless of what’s going on around a given area, thermals are almost always very localized events. If the sun heats up one area of a field before another, it’s going to cause thermal air currents to rise in those spots first. The same holds true for hillsides. For example, it can take longer for the sun to heat up north-facing hillsides and get the thermals rising in those areas. Even vegetation type and density, such as a stand of conifers that hold heat well and produce good thermal bedding, can impact thermals. It has less of an effect, of course, but still has influence.

Due to all of these factors, and more, to truly learn how wind currents and thermals affect a property, it takes experience hunting that particular area. That can take years, or it can be learned quicker.

Still, no matter what thermal event you’re dealing with, they create wind currents that carry your scent. And deer know it.

Whitetails Love Thermals

Deer are prey animals, and they’re constantly being targeted by Mother Nature’s fiercest warriors. Because of this, they become very familiar with their home ranges, which are approximately 640 acres, and especially their core areas, which are 30–75 acres — habitat and location depending.

Here’s a common comparison. People know everything about their houses. If something is out of place, it’s generally noticed. The same is true for the land a whitetail inhabits. Deer know everything about their “house,” too, and they use that to their advantage.

They’ll choose bedding areas and travel routes accordingly. They’ll use beds, trails, water and food sources, but only when the conditions are right to use them, or travel in that direction. This is especially true for bedding areas and travel routes.

No, deer don’t always walk into the wind. But they do use the wind in their favor, and that includes thermals. For example, during the rut, bucks commonly cruise benches and ridgelines in the morning when thermals are rising, because this allows them to scent-check almost everything down below them.

On the flip side, in the afternoon, deer like to enter the open from the lowest points in the area. They do this because cooling, late-afternoon thermals push the air downward to the lowest points. When deer travel through these lower areas, they smell everything that wafts down into the bottoms.

Because deer are crepuscular animals, thermals typically top-out during peak movement times — dawn and dusk. This makes some spots simply unhuntable. Other areas might seem to be, but serve as excellent spots thanks to certain “glitches” in the system. Regardless, it’s crucial to be able to read the terrain, gauge the wind and thermals, and then use all this learned info against the deer you’re after.

Use It Against Them

Deer use areas when the wind is good for them, or at least when they think it’s in their favor. As hunters, we can turn that around on them. While it can certainly work, don’t just hunt when the wind and thermals are seemingly perfect for you, and thus, the exact opposite of what a deer would want.

Instead, hunt just-off winds and thermals, too. It’s a highly risky move most times, but it can certainly pay off. A lot of big bucks have been killed by hunters whose scent drifted just outside of the deer’s scent cone.

It’s a safer play to take advantage of traditional thermals. In the morning, the tops of ridges are usually best for accomplishing this. Hunt above the deer, and you’re golden. Most of the time, scent starts out well above their heads, and keeps on rising.

Hunting along benches is another great way to take advantage of morning thermals. Depending on the elevation of the bench, when the prevailing wind is blowing perpendicular to it (in either direction), the rising thermals will meet the prevailing wind and then glide off somewhere in the distance. However, this becomes a problem when the prevailing wind is blowing parallel to the bench. Then, the rising thermals head uphill, hit the bench, and then get intercepted by the prevailing wind, which can launch your scent down the bench toward deer. Sometimes, if the thermals are strong enough, they can overcome the prevailing wind. But it doesn’t always happen that way.

Things change in the afternoon, when thermals begin to drop and the wind may or may not override them. Still, when it feels dead calm, you’ll see the air current drifting downhill. So, because of this, set up downhill from expected deer travel routes.

Basics aside, take advantage of pinch-point-related terrain features commonly found in hilly topography. Examples include saddles in rock walls and ravines separating ridgelines. Deer will likely have to pass through these areas, regardless of whether the wind and thermals are in their favor.

That said, it’s still best to have as many stand sites as possible. Having numerous ambush options gives you choices, while also providing likely hunting opportunities that will work for the winds occurring on any given day. Having more stands isn’t the only precaution, though.

Taking advantage of thermals demands extensive knowledge of them, and even requires being able to time these thermal-direction changes. Once the thermals change, it can end a hunt for that particular area. To predict these shifts, check the forecasted temperatures. As long as temps are rising fairly quickly, thermals will likely continue rising with them. If temperatures level out, thermals will slacken and the prevailing winds will take over.

Also, never assume the wind is doing what your preferred weather app says it is. Terrain, and especially thermals, can influence this. For example, your weather source might read north, but the local ridge network might produce more of a northwesterly direction. Furthermore, most weather sources don’t factor in thermals, either.

All things considered, scout the land you plan to hunt. Walk the bedding areas, and even pick out trees that work best for the average thermal conditions. Test the wind while you’re there. Get a feel for the area. Then, mark the specific location on an app or map.

Once in the field for the hunt, doublecheck for sign, and then make an educated guess as to where to place your chips. And despite all of the mad-scientist strategizing, remember to at least have a little fun.

App Masters

Those who want to master thermals will find some aid with certain hunting apps, such as HuntStand. This app offers an abundance of useful tools, but one of them is monitoring, recording, and tracking wind currents. This app has numerous layers that show terrain and topography. These are great for revealing bluffs, ridges, hills, valleys, and other areas where thermals have bigger impacts. Use these to find potential hotspots, and then to remember them by.

Of course, the one-two combination between the wind and thermals can make these less predictable — at least until you get to know a specific area. So, use this app to keep tabs on how certain wind directions and thermals play out. Then, keep notes on how particular deer habits correlate with these specific conditions.

*The author lives in the hills of Kentucky, spending his time hunting critters and working full-time handling all things media.

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