Understanding Thermals | Hunting Mornings VS Afternoons

How To Use Thermals When Hunting

A deer’s number one defense in the woods is his nose. You can wear the perfect camo, be an expert with your weapon, and hunt the best property; but if you aren’t hunting a buck’s nose he will beat you every time. According to research done at Mississippi State University, a deer’s sense of smell can be as many as 1,000 times more acute than humans. Successful deer hunters hunt a deer’s nose.

Any hunter who has spent much time pursuing whitetails won’t be surprised to hear how amazing a deer’s olfactory system is. The simple answer is to hunt the wind. Hunters have used the wind to pursue game and cover their scent, probably since the dawn of hunting. Hunting the wind may seem uncomplicated and straightforward, and primarily it is, but not so fast. Thermal air currents can really throw you a curve ball, just when you think you’ve got the wind figured out.

What are Thermals?

Thermals, thermal air currents, or thermal columns occur when air near the earth’s surface becomes heated by the sun and expands. Warm air is less dense than the surrounding air and it rises. This phenomena of rising warm air in turn creates a downward-moving column of colder air that takes the warmed airs place. To sum it up, warm air rises, and cooler air sinks to take its place. The size and strength of thermals is influenced by a number of things like topography, cloud cover, and humidity. The key concept for hunters when it comes to thermals, is that thermals can act like wind. A downward or upward moving thermal will carry scent the same way that air currents and wind do.


How do you Hunt Thermals?

There is no magic recipe or end all steadfast rule when it comes to hunting thermals, but by understanding how thermals work, and how they affect hunting, you can use them to your advantage. Thermals are an effect of the sun and its warming rays, in order for an upward thermal to build, air must first be warmed by the sun. Early in the morning, before the sun’s rays haven’t taken affect, the ground may not be warm enough to create an upward thermal. In fact, a downward thermal caused by air cooling overnight may still be sinking cooled air downhill. This means if your morning stand is uphill from a food plot, bedding area, or game trail you could be hunting directly upwind of the deer you intend to target first thing in the morning and not even realize it.

The effects of the warming sun rays on a morning hunt can change thermal properties and air flows in a matter of hours, and maybe even minutes. As a general rule of thumb when hunting on or near slopes or steep terrain, hunt high (or above deer) in the mornings and low (or below deer travel routes) in the evening. Weather, cloud cover, fog, and precipitation all have direct effects on thermal air currents and how your scent travels. Keep in mind cool air will settle in the lowest place and your scent along with it. Hunting a ridgeline stand above a well traveled deer trail on a cool foggy day, or on an evening hunt may very well cause your scent to travel directly into the area you expect the deer to be.


North and South Facing Slopes

Remember the sun and its warming affects are the largest factor when it comes to thermals. The aspect of a slope and the amount of sunlight a face receives will directly contribute to the thermals on the ground there. In the northern hemisphere southern facing slopes receive the sun’s earliest rays, warming them first and creating the mornings first thermals. Conversely, northern slopes remain shaded longer, and cooler. The thermal properties and air current action on a northern slope will take place later in the morning than a southward facing slope.

Identifying Thermals and Check the Wind Often

Hunting mountainous, hilly, and steep terrain can offer great rewards. Deer find refuge in steep canyons, along deep valleys, and on hill sides. For the hunter, these areas offer the greatest challenge when it comes to hunting the thermals. Hunters must stay flexible, adapt, and aware of the thermal action around them.

By using satellite imagery and topo maps you can identify areas that will receive the earliest morning sun, and predict the thermal flow around slopes, funnels, and bottom areas. Take into consideration what aspect slopes or hillsides are facing, and shadows that the adjacent landscape will create. In the morning warmed air will flow upward along the slope, following the path of least resistance. By combining the wind direction and thermal air flow, you can position yourself for a successful hunt. In the evening, the reverse is true, and cooled air will settle into low lying areas. Staying low on an evening hunt will help keep your scent off the hillside.

Remember, just like the wind, thermals can change and change often. Although the hunt high in the morning and low in the evening is a general rule, there are too many factors to always rely on it. Check the wind often with a wind checker to know not only what the prevailing winds are doing, but how thermals are affecting air flow and your scent column where you are. Don’t be surprised to see changes in air currents throughout the course of a days hunt, caused solely by thermals.

Putting it into Practice

Ridge tops, creek bottoms, and steep terrain can be an optimal location for hunting deer. Studying these areas with plat, topo, and satellite imagery mapping technology to identify bedding, travel, and feeding areas is an exceptional way to identify your hunt locations, stand setups, and your way into and out of the hunt. Wind direction plays a critical role in all these factors, but don’t forget how thermals will affect your hunt as well. Be sure to consider the time of day, the warming sun’s rays and their effect on thermal action when you are planning your hunt.