Elk Hunting Forum - Understanding Mountain Thermals

[cnelk]

I thought TACTICS would be a good place to discuss \'Thermals\' as they go hand in hand with tactics.
Some may recognize the info, but its still good to know

Im starting this topic for anyone that may be interested and hoping others will contribute and ask questions:
So here goes:

Thermals should not be confused with Wind.
Thermals are driven mostly by the heating/cooling of the earth surface

Thermals are very gentle movements of the air, sometimes almost imperceptible.
Cold air sinking below the rising thermal causes a downdraft.
That\'s why you can feel thermals in your face in one spot, then feel it on your neck in another.

Typically the thermals move DOWNSLOPE in the mornings until the air heats. When the air heats up, it mixes.
After the air heats up and stabilizes, the thermals will be UPSLOPE during the day.
Later in the day, as the air starts to cool, the thermals will mix again and then just before dark, they will be predominately DOWNSLOPE again

Thermals are weather dependent. You wont have any consistent thermals if a weather front is moving thru.

Slope direction definitely has an impact. The sun or prevailing wind will warm one side or mix it before the other.

Here\'s some more info regarding thermals...
Downslope wind?

1. A wind directed down a slope, often used to describe winds produced by processes larger in scale than the slope. Because this flow produces subsidence, downslope winds experience warming, drying, increasing stability, and clearing if clouds are present.

2. Flow directed down a mountain slope and driven by cooling at the earth\'s surface: a component of the mountain?valley or mountain?plains wind systems; same as katabatic wind.

The many synonyms for downslope flow are sometimes used interchangeably, and this gives rise to ambiguity and confusion. Downslope can be used generically to denote any wind flow blowing down a slope, or it is used specifically for katabatic flows on any scale, such as the nocturnal slope-wind component of mountain?valley wind systems or mountain?plains wind systems.

See katabatic wind, gravity wind, drainage wind, fall wind, bora, foehn, chinook.

 

[cohunter14]

Thermals are very gentle movements of the air, sometimes almost imperceptible.

Here is a question for you Brad: I have noticed that sometimes you cannot necessarily feel thermals as wind. However, you can feel the difference in temperature, justifying that the thermals are there. So if you can feel the difference and temperature and know the thermals are there, but don\'t sense any wind at all, do you still worry about the thermals? Complicated question, but something I just thought of. I have always been curious to know what you archery hunters do when there is no wind at all to be felt :think:

 

[cnelk]

Derek
Very seldom is there no thermal, breeze or wind.
I tend to use my wind checker MORE when the thermal is imperceptible just to be sure

 

[WW]

If you think of morning and evening thermals as water flowing down hill it will help to understand maybe a little better. From where you are standing on a mountain side, if you pour a glass of water on the ground, which way would it flow? Thermals do the exact same thing! So just think of them a water flowing down hill.

Then as the sun warms things up, I\'m sure you can relate to the fact that heat rises. The updraft of the heated air represents the uprising thermals. It ain\'t rocket science!

Some things that can disrupt thermals or the timing of when they shift could be wind, storms, cloud cover, and even which side of the mountain you are on. Thermals can be flowing down on one side of the mountain while they are rising on the other side. This is especially true on north/south running canyons. In the morning, the west facing (east side of the canyon) the thermals can be flowing downward because it is still in the shadows. But over on the other side, the sun is warming things up and the thermals are starting to rise.

There are also a few places where the thermals tend to flow down hill regardless of the time of day. These are usually deep/tight drainages that have a cool spring fed stream flowing down through the bottom of them.

I even know of one place where the thermal flows up hill all night long. I have no explanation for that!?!? The only thing that makes any since at all is maybe there is such a strong downward thermal that the valley below fills up and forces some air to over flow out the top. Kind of like over filling a cup. I know of only one place where this happens and it is one of my favorite hunting spots. As I drop down into the place about twenty yards or so, everything becomes normal and the thermal once again starts flowing downward. It\'s a weird place and I have never figured it out in all the years I have hunted there.

 

[Deertick]

WW ... I think you\'re right with the \"overflowing cup\" theory.

Imagine a chunk of dry ice sitting on an object in a sink. First, the \"fog\" falls down, until it fills up the sink, then it has to \"overflow.\"

That\'s why I don\'t think there is a standard description of thermals ... mountains with valleys are different from isolated ranges where the thermals can \"pour\" endlessly down and out onto the plains.

But valleys fill up ... and the \"flow\" seems, to our eye, to reverse.

 

[Bob Frapples]

Like brad said, I\'d be using the wind checkers way more often in the unperciveable wind. It\'s very rare to find air perfectly still, even though it is undetectable to our crude senses.

I find I get busted more often when there are little winds, partly, Im sure due to lack of other background noises and movement the winds generate. I visualize it as being a human stink machine generating smell just like a Halloween punch bowl. The aroma stays more concentrated and does not get broken up and dispersed nearly as readily in these type conditions.

Few of us will never be able to predict wind direction 100%, we can anticipate it and learn the fundamental mechanics of it, but there are LOTS of variables controlling it. Keeping constant tabs on it, especially when we don\'t think it thre, is the best answer.

 

[trophyhill]

Quick question. How far will thermals carry human scent and how rapidly does human scent dissipate when carried by thermals?

 

[Bullnuts]

Scent is something different altogether and depends a LOT on humidity and temperature, and also where the thermal picked that scent up. In my experience, scent dissipates quickly under direct sunlight. It doesn\'t have to be blazing hot, but the sun does cook scent off. Scent, like water, will pool in low places. So if you decide to take a break and sit down for a while, do it in the sun and not in a hollow spot in the shade. Humidity is another factor. A lot of guys think that scent will stick around longer if there\'s a lot of moisture in the air. I don\'t necessarily agree with that. I believe that the best scenting conditions occur when there is low humidity, but cool temperatures. This allows the scent to remain in the air longer without being baked off. Humidity causes the scent to fall to the ground faster because the water molecules are much heavier than the scent molecules and they tend to trap the scent molecules and take them downward instead of upward where they have a better chance of floating on the wind.

 

[WW]

I have played around with mule deer by getting up wind and gradually working in towards them. At 400 yards directly up wind there was no reaction at all from the deer. At 300, basically the same. But at 200 yards they threw there heads up for a look around. The next couple of steps I made and they were out of there like a speeding bullet. I always thought that they probably smelled me long before I reached that 200 yard danger zone. But my scent was probably broke up enough that it really didn\'t alarm them. This is where I think that scent eliminator spray may be helpful. It probably doesn\'t kill all your scent, but it may deaden it enough to make you seem farther away than you really are .

This by no means is a scientific study. But if you happen to live in muley country, they are easy enough to find. So why don\'t you try what I did and report your findings back here.

 

[WW]

Thanks Brad. Can we archive that?

 

[cnelk]

Yes, JF placed this in archives.