Thermals - Consistency

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Huntress13
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Thermals - Consistency

Unread postby Huntress13 » Thu Aug 29, 2019 2:33 am

I have a question that I've never quite seen an answer on about thermals. Just watched Hill Country Bedding. We have more rolling hills than steep ones, if that matters.

We get several days during hunting season where there are cold fronts. So the temp during the day is going to stay the same as the night before and isn't going to rise, or maybe the temp during the day might drop below the overnight temp. Often we get more cloudy days than sunny.

Are the thermals still going to rise on those days? Or maybe there are still thermals but they aren't as intense as a day that is sunny and the temps are going to warm through the day? What say the experts?

Edit: I meant to add, perhaps if that is the case, the bucks don't choose to bed on the hill in those situations?


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Re: Thermals - Consistency

Unread postby jwilkstn » Thu Aug 29, 2019 4:02 am

During a front, the wind is usually blowing strong enough to trump any thermal effect.
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Re: Thermals - Consistency

Unread postby elk yinzer » Thu Aug 29, 2019 4:19 am

Yes and no. The concept of thermal columns is really simple. Sun heats the ground, warm air is less dense and rises. In practice there are infinite complex interactions that drive the air currents we experience hunting. The more complex the terrain, the more complex the air currents become as any hill country hunter can attest. Unless there is 0.0 atmospheric wind, it's a gross oversimplification to think of thermals in a singular dimension as if they just rise and fall, period. Yes, thermal effects still occur on cloudy days. The ground is still absorbing solar radiation through the clouds, generally speaking. Of course on really dark hillsides where the canopy blocks most of the sunlight can effect that. All that is really saying is thermals are complex and milkweed experimentation is your best friend.
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Re: Thermals - Consistency

Unread postby backstraps » Thu Aug 29, 2019 4:24 am

There are going to be days when the thermals aren’t as strong as others.....but

It literally only takes a couple degrees difference to create a daytime rising thermal

On the days when the air temps stay steady... but the sunshine can hit the bottom of a valley, that valley air temp could easily increase a couple degrees and thermals will begin rising

I have hunted days where the temp is dropping but the sun is bright, thermals were pulling up hill fast
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Re: Thermals - Consistency

Unread postby Huntress13 » Thu Aug 29, 2019 4:26 am

jwilkstn wrote:During a front, the wind is usually blowing strong enough to trump any thermal effect.


What if the wind isn't blowing hard? The front came through already, and now it's just a grey calm day where the temp isn't rising any? We also see a lot of strange weather from the Great Lakes, what is happening one place is different 20 miles away from the lake. Michigan and upper Wisconsin folks can probably relate.
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Re: Thermals - Consistency

Unread postby Huntress13 » Thu Aug 29, 2019 4:28 am

elk yinzer wrote:Yes and no. The concept of thermal columns is really simple. Sun heats the ground, warm air is less dense and rises. In practice there are infinite complex interactions that drive the air currents we experience hunting. The more complex the terrain, the more complex the air currents become as any hill country hunter can attest. Unless there is 0.0 atmospheric wind, it's a gross oversimplification to think of thermals in a singular dimension as if they just rise and fall, period. Yes, thermal effects still occur on cloudy days. The ground is still absorbing solar radiation through the clouds, generally speaking. Of course on really dark hillsides where the canopy blocks most of the sunlight can effect that. All that is really saying is thermals are complex and milkweed experimentation is your best friend.


I will definitely be checking it out and making notes.
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Re: Thermals - Consistency

Unread postby backstraps » Thu Aug 29, 2019 4:30 am

I was trying to think of a better example:

I know you have walked down into a valley or hollors as we call them, and you can easily feel the air temp is cooler

So if the air temp in the valley was 5 degrees cooler than the air temp on top of the ridge (very common around me) and the sun made its way to that cooler air pockets. Then the sun is going to quickly raise that lower air temp down there. 1-2 degrees warmer down there will get thermals climbing the aide of the hills fast!
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Re: Thermals - Consistency

Unread postby Huntress13 » Thu Aug 29, 2019 4:41 am

backstraps wrote:There are going to be days when the thermals aren’t as strong as others.....but

It literally only takes a couple degrees difference to create a daytime rising thermal

On the days when the air temps stay steady... but the sunshine can hit the bottom of a valley, that valley air temp could easily increase a couple degrees and thermals will begin rising

I have hunted days where the temp is dropping but the sun is bright, thermals were pulling up hill fast


Early season we have more sunny days. But get past a certain point in the season, then clouds prevail more than not. And as I mentioned in another reply, what is happening on the Great Lakes makes a big difference, and just a few miles down the road the conditions are completely different.

I was trying to think of a better example:

I know you have walked down into a valley or hollors as we call them, and you can easily feel the air temp is cooler

So if the air temp in the valley was 5 degrees cooler than the air temp on top of the ridge (very common around me) and the sun made its way to that cooler air pockets. Then the sun is going to quickly raise that lower air temp down there. 1-2 degrees warmer down there will get thermals climbing the aide of the hills fast!


I'll have to start a file to keep track of the conditions and observed thermals. Not sure my hills are extreme enough to have that much difference. For example on our land, it is mostly a flat for half a mile in either direction, but there are small hills at both ends, drumlins, a few hundred feet high in a short space.
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Re: Thermals - Consistency

Unread postby jwilkstn » Thu Aug 29, 2019 5:39 am

Huntress13 wrote:
jwilkstn wrote:During a front, the wind is usually blowing strong enough to trump any thermal effect.


What if the wind isn't blowing hard? The front came through already, and now it's just a grey calm day where the temp isn't rising any? We also see a lot of strange weather from the Great Lakes, what is happening one place is different 20 miles away from the lake. Michigan and upper Wisconsin folks can probably relate.


I'm in Tennessee, so I don't think you will benefit from my input on lake effect from the Great Lakes lol.

In my part of the country, we get predictable north winds and clearing skies following the passage of a front.

I agree completely with the comments above as far as thermals on calm days and days when the air temp isn't rising.
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Re: Thermals - Consistency

Unread postby stash59 » Thu Aug 29, 2019 5:51 am

No matter the temp or how much the sun shined. There was always a thermal rise at some point during the day. When I was in the mountains out in Montana.

Now they may not have been constant. Alot of times the thermals, prevailing winds and whatever else affects air currents. Would fight each other, one or the other taking over for a few moments. Tough days to hunt. Thus the need to constantly check what the "wind" is doing!

As far as your "little" 100' hills. That's plenty of elevation change to get thermal pulls daily. Heck if you really check things out. 5' or 10' is enough to get some. At least right at ground level or in the first couple of feet above the dirt.

It's basically a pressure thing. The warmer air isn't only pushing upward, it's kinda pushing outward too. Like water it takes the path of least resistance. But add in obstacles and you get things like eddies, etc.

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Re: Thermals - Consistency

Unread postby Huntress13 » Thu Aug 29, 2019 8:43 am

Thanks for the info!
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Re: Thermals - Consistency

Unread postby <DK> » Thu Aug 29, 2019 10:58 am

There is always some type of thermal effect. Even rainy and/or cloudy days. Obviously the best days are clear,sunny and its no coincidence thats when I see alot of deer move or killed.

As far as consistency goes, I see the steep cliff edges having a strong upward pull. It seems that drastic, sheer drop just brings it up faster. Also no coincidence I find bedding on those edges, especially if there is access or parking below.

A few things besides thermals I like to pay attention to is wind kick back. So if I have 2 ridges running parallel, one ridge is taller than the other I deal with alot of blow back or kick back. The wind hits the other ridge side and kicks straight back to the leeward side im trying to hunt. Not swirling. This only happens in certain spots but I have noticed its bc im 1/2 or lower on the ridge or steep draws can cause this issue.

One other tip ill throw out for hunting hills is pay close attention to changes in wind forecast and plan for issues. So if the wind is S for 2 days and all night leading to the hunt. Then it switches to W @ 6am - that is not much time between the switch and time to hunt. It could take until mid-morning before those winds stay W and bc it was S wind for 2 days you could see random gusts from the S. On the flip side - a buck could go to his S wind bed early am, then switch to his W midday.

If the wind has been indecisive for a few days (N/S/E/W) and the day you hunt is variable-5mph then you could see random wind gusts all day.

Best advice Dan or anyone can give about it is view it as flowing water.

So aside from thermals, I try to pay close attention to x2 factors;
*Previous/Current/Future Daily & Hourly Wind Forecasts
*Terrain features Up/Down wind about 200 yards or more.

Both will have a major effect on what happens with the wind.
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Re: Thermals - Consistency

Unread postby backstraps » Thu Aug 29, 2019 12:52 pm

<DK> wrote:There is always some type of thermal effect. Even rainy and/or cloudy days. Obviously the best days are clear,sunny and its no coincidence thats when I see alot of deer move or killed.

As far as consistency goes, I see the steep cliff edges having a strong upward pull. It seems that drastic, sheer drop just brings it up faster. Also no coincidence I find bedding on those edges, especially if there is access or parking below.

A few things besides thermals I like to pay attention to is wind kick back. So if I have 2 ridges running parallel, one ridge is taller than the other I deal with alot of blow back or kick back. The wind hits the other ridge side and kicks straight back to the leeward side im trying to hunt. Not swirling. This only happens in certain spots but I have noticed its bc im 1/2 or lower on the ridge or steep draws can cause this issue.

One other tip ill throw out for hunting hills is pay close attention to changes in wind forecast and plan for issues. So if the wind is S for 2 days and all night leading to the hunt. Then it switches to W @ 6am - that is not much time between the switch and time to hunt. It could take until mid-morning before those winds stay W and bc it was S wind for 2 days you could see random gusts from the S. On the flip side - a buck could go to his S wind bed early am, then switch to his W midday.

If the wind has been indecisive for a few days (N/S/E/W) and the day you hunt is variable-5mph then you could see random wind gusts all day.

Best advice Dan or anyone can give about it is view it as flowing water.

So aside from thermals, I try to pay close attention to x2 factors;
*Previous/Current/Future Daily & Hourly Wind Forecasts
*Terrain features Up/Down wind about 200 yards or more.

Both will have a major effect on what happens with the wind.


Excellent post!! Very good points being made here :clap:
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Re: Thermals - Consistency

Unread postby Huntress13 » Thu Aug 29, 2019 11:15 pm

Wow, thank you DK. That is good info.
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