Planning for thermals

Share your tips and techniques on these great, but often times lost methods of hunting.
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Planning for thermals

Postby tonyotony » Sat Sep 04, 2010 11:42 pm

When I first started hunting, I didn't even pay attention to the wind; I thought scent control was all I needed! Ha Ha! Now that I'm learning about thermals, I'm trying to plan for that. With regard to thermals, I've read that it's a good idea to hunt your ridges and more elevated location blinds in the morning, as the thermals are rising with the temperature, thus pushing your scent up and away, and hunting the ravines and low-lying blinds in the later afternoon and evening. Anyone have thoughts on this? Seems like it would affect a ground hunter more than a treestand hunter, and I'm trying to plan for it, since I'll be hunting an area that has both low-lying and higher areas, but i can move fairly easily from one to the other, since they are not mountains, just hills and valleys.

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RE: Planning for thermals

Postby Woods Walker » Sat Sep 04, 2010 11:59 pm

For a ground hunter thermals are a "biggie" for sure. What you describe is a point. Thermals are generally a bigger concern when there is little or no wind, as even the slightest thermal will have an effect then. Just one more reason why I prefer windy days for stillhunting.

A good way to get an idea of thermals in your area is to get some colored smoke bombs (the kind you see at any fireworks store), and use them when you scout in the early mornings and evenings. I even like to use them on windy days along ridgelines and saddles, and what they can teach you about where the wind swirls on terrain features will surprise you. Wind is like flowing water, in that there's a main "current", and then eddies and still pockets as it moves along the terrain.

Once you get a feel for thermals, you can actually start to "feel" them, espcially in the evening of a warm day, when as the sun starts to set you suddenly feel cooler air moving along the ground as sinks to a lower elevation. A smoke bomb will confirm this. I also am never without a puff bottle of scentless wind powder when I hunt just for this reason.
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RE: Planning for thermals

Postby shaman » Mon Sep 13, 2010 11:24 pm

tonyotony:  You need to rearrange your thinking just a tad.  Think of what happens when the sun comes up.  As soon as it starts hitting the treetops, the sun will start warming air that in turn will suck more and more air upward.  However, before the sun really gets to working, the general flow of air will be downhill, hugging the ground.  I would generally fix the time that things change over to the point where I start to feel the sun's heat.

Let's just say the sun rises at 7, and there's no wind.  You're in a blind on top of the hill, overlooking a ravine.  From the time you get to your blind until probably 0900 the airflow will be down hill in front of you.  After that, it'll reverse and start coming back up into your face.

If you're in the bottoms, the general airflow pattern until 0900 will be mostly stagnant.  Your body heat will carry the scent upwards.  However, once the sun starts warming the hilltops, the draft will cause swirling and the flow will be generally uphill towards the part that's getting the most sun.

Now let's say its afternoon.  The draft has been coming uphill all day.  On the hilltop, there will be a marked shift as the sun sets.  As soon as the lower elevations stop getting sun, the air will cool and sink, sucking air downhill from the top.  Down in the bottoms, there is again this swirling as the flow adjusts.  If you're in a fairly tight ravine, you'll also get a flow generally down and out of  the bottom of the ravine.

On flat ground, things change, but it's still all powered by the sun.  Let's say you're hunting a field surrounded by woods.  The air in the middle of the field has been unprotected all night, and has cooled more than the protected woods.    The air from the center of the field will try to find the lowest point it can, sucking air from the surrounding woods in over the top of the cooler air.  When the sun hits the treeline at the edge of the field, the flow will change.  When the sun hits the center of the field, it'll change still again.  If you're hunting the edge of that field, you may encounter several changes from 0600 to 1000, and then again at 1600 until dark. 
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RE: Planning for thermals

Postby tonyotony » Sat Sep 18, 2010 3:38 pm

I'm hoping it's windy!! Thanks for the great explanation.

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RE: Planning for thermals

Postby charlie 01 » Fri Oct 08, 2010 7:14 pm

Aren't you glad you asked. I hope it is windy for you too. All I know for sure, is that on a stormy, rainy, cloudy day everything goes down. I remember driving by people's houses that burned wood for heat. On those days the smoke would come out of the chimney and go right down to the ground.
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