Thermals?????

[MUSKY18]

Can someone explain to me exactly what Thermals are and how they work and affect your scent?

[musky hunter]

As i understand a thermal, it's a movement of light wind caused by the localized heating of the earth. If you were on a hillside on a calm day, as the sun warms the hill, you can get a slight draft up the hill. When the sun retreats, the thermal ends. As the day progresses, the prevailing wind direction may be influenced by the thermal effect. A building thermal may carry scent up and away from the ground, a dying one might bring your scent closer to the ground. Knowing all this is supposed to help you place your stand where you have the least negative influence given the normal thermal activity. And some people do have some of this figured out. I say the average hunter is better off controlling sweat, spraying down, washing clothes in scent free soap, and getting the stand as high off the ground as practical, and doing all the things to reduce scent as possible.

[DonBo]

It's as simple as warming air rising and cooling air decending. Prevailing winds eliminate much of the thermal movement.

As for stand placement what it means is, in the morning, while still cool, the deer downhill from you may catch your scent. As the day warms the deer uphill from you will be in your scent stream. Then it reverses again later in the day as the air begins to cool.

I have a spot in a river bottom in the Black Hills where you can bet that later in the day as it cools, the wind will blow downriver. Happens everyday, UNLESS there is enough wind to negate any thermal issues.

Hope this helps.

[B. Amish]

i get busted by thermals when i bowhunt up hill from a swamp in the evening. usually it's earlier in the fall when you can really feel the temp drop when the sun goes down. all that cooler air drifts to the lowest spot - the swamp. thats where the deer bed and thats why i would get busted, even though i thought i had a good wind.

took me a while to put 2 and 2 together on that stand and why i always seemed to get busted.

[Stratosman]

Actually I believe the opposite holds true...during the day the earths surface temps is warmed by the sun. Sice earth retains heat longer than the surrounding air, during the nighttime hours the earth heats the layer of air closest to it, as it does, air bubbles of warmer air rise from the earths surface, they continue to rise until they are the same temp as the surrounding air. This is what we see in the morning, so if you are hunting hillsides or ravines, set up above the deer. As the sun sets, the lower elevations see the air temps cooler than those above and therefore will tend to "sink", or go downhill....

Of course any air currents dictated by wind speed and direction will negate the effects of thermal movements. As a general rule, I always set up ABOVE where I expect the deer to move as thermals are more prevalant in the morning when wind speeds are tyically minimal. During the evening most times there is still anough of a breeze to negate thermals

[Scoot]

Lots of good information here and some definite misinformation too. First, the most common/typical scenerio-- in the early AM the temps continue to cool and the thermals will move air dowhill. At some point in the morning, the air temps will begin to warm up (again, this is typical, but not always). When the temps begin to warm up, the air will move uphill (this often starts to happen around 10:00, but that can vary due to a ton of factors).

In the evening, the opposite happens- warm temps have the air moving uphill. As the evening approaches, the temps begin to cool off and the air moves more downhill.

A couple things: during the time when the thermals switch the wind from downhill to uphill (in the AM) or uphill to downhill (PM), the winds tend to be very shifty and unpredictable. This can be a tough time to make much sense of them and they will often undermine efforts on a critter. Also, the prevailing wind plays a significant role here- in areas where the prevailing wind is blowing one direction, it might meet the wind coming from another direction due to thermals. I see this all the time out West- the wind is coming out of the East up on top, but when I reach the edge of a hill, the wind is coming directly up the hill from the West.

A really good tip is to pay attention to how a big buck is faced when bedded down. Mule deer are really good at this- they will face their butt into the wind. This will let them smell what they can't see and see what they can't smell. I can't tell you how many times I've watched a muley bed down so he is situation this way, then turn 180 degrees and rebed when the thermals switch from downhill to uphill. I've also seen a lot of muleys in their beds facing the "wrong way" and they should be "easy sneaks", only to get up there to find the wind is going the opposite direction from the place I was glassing from. This always results in me sneaking on an empty bed, from a buck that smelled me. Those big muleys don't get big because they are dumb...