Lake Thermals

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Brad
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Lake Thermals

Unread postby Brad » Sat Dec 18, 2021 4:55 am

I've got a spot with a 95 acre lake surrounded by timber with hill points that has doe and buck bedding. I am having trouble recalling exactly how the lake will effect the thermals in a spot like this.

As the air temp gets colder, in the winter:
I assume the water temp is higher than the air temp. In the morning therefore the air will rise over the lake and pull the thermals down the hills and toward the lake before there is any radiant heat on the hillsides? then once there is radiant heat from the sun on the hills, the thermals will pull up the hill...? does this sound correct?
Then in the evenings The thermals will switch from rising up the hillside to dropping down toward the lake? This is what I would assume happens when there is no lake to effect the thermals, but is this what would happen with the lake there as well? below is an example of the place I'm talking about. In this specific location I have seen alot of deer traffic (mostly does and younger bucks) with an intersection of travel at the X. In this particular spot it seems the deer start showing up moving from west to east and from south to north.
So basically, aside from the normal higher and lower elevation creating thermal flow, how will the lake play into the thermal flow? On top of that, how will the thermals be pulling toward the "fingers" of the lake between the timber points, and the larger body of water to the north of the picture? Will there be some pull more north/south as well? or will the pull be mostly straight to/from the fingers?

lake thermal - low.jpg
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Re: Lake Thermals

Unread postby PK_ » Sat Dec 18, 2021 6:49 am

Thermals will pull to the warmer spots. It’s really hard to give you anything specific beyond that. But typically they will drift down each hillside into the cove and then out towards the main channel where the water is a bit warmer as it gets the most sun exposure.

Understand that wind moves very quickly over open water so even a very small amount of wind really disturbs the thermal flow on lakes. Also when the temps stabilize and the water/air temps get close, the thermal flow will be very weak to begin with, sometimes non-existent.
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Re: Lake Thermals

Unread postby Brad » Sat Dec 18, 2021 8:02 am

PK_ wrote:Thermals will pull to the warmer spots. It’s really hard to give you anything specific beyond that. But typically they will drift down each hillside into the cove and then out towards the main channel where the water is a bit warmer as it gets the most sun exposure.

Understand that wind moves very quickly over open water so even a very small amount of wind really disturbs the thermal flow on lakes. Also when the temps stabilize and the water/air temps get close, the thermal flow will be very weak to begin with, sometimes non-existent.



In the morning would the water temp be warm enough compared to the air to have the same thermal effect before the sun hits the hillside? I am not certain what the water temp is, but now thinking about it, I can't imagine it would be more than around 45 degrees and probably not much less than 40 degrees, but that's a guess. Anybody know how much of a temperature difference it takes to make a noticeable change in thermal effect? I would even think the sun exposed hillside on the other side of the creek, plus the water in the lake, and being on the shaded vs sunny side of a hill... alot of variables to consider.
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Re: Lake Thermals

Unread postby nsmith253 » Sat Dec 18, 2021 8:33 am

I used to hunt a permission property that had Lake Michigan frontage. Big steep wooded ravines coming up from the shoreline with drainages down to the lake. The only way I could figure out what was happening was to bring milkweed and test it, it was very spot-specific and most of my predictions were wrong or only true for short distances.
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Re: Lake Thermals

Unread postby DaveT1963 » Sat Dec 18, 2021 9:53 am

Wind structure and shade will vastly affect thermals on a large body of water such as a lake. You can use that to your advantage by paying attention to Steep bluffs, heavy forests, etc.....

Everybody wants a simple formula for thermals but in reality thermals don't always go straight up and straight down there's far more to it than that.
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Re: Lake Thermals

Unread postby Brad » Sat Dec 18, 2021 11:43 am

DaveT1963 wrote:Wind structure and shade will vastly affect thermals on a large body of water such as a lake. You can use that to your advantage by paying attention to Steep bluffs, heavy forests, etc.....

Everybody wants a simple formula for thermals but in reality thermals don't always go straight up and straight down there's far more to it than that.


I'm certainly not looking for a simple formula, just looking for others insight on how the addition of a lake thats around 94 acres in the close proximity to some rolling hill points would likely effect the thermals compared to the same terrain without the lake.
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Re: Lake Thermals

Unread postby DaveT1963 » Sat Dec 18, 2021 12:18 pm

Brad wrote:
DaveT1963 wrote:Wind structure and shade will vastly affect thermals on a large body of water such as a lake. You can use that to your advantage by paying attention to Steep bluffs, heavy forests, etc.....

Everybody wants a simple formula for thermals but in reality thermals don't always go straight up and straight down there's far more to it than that.


I'm certainly not looking for a simple formula, just looking for others insight on how the addition of a lake thats around 94 acres in the close proximity to some rolling hill points would likely effect the thermals compared to the same terrain without the lake.


I hunt lakes a lot down south. Shade is a huge factor in a lot of cases.
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Re: Lake Thermals

Unread postby Brad » Sat Dec 18, 2021 1:30 pm

DaveT1963 wrote:
Brad wrote:
DaveT1963 wrote:Wind structure and shade will vastly affect thermals on a large body of water such as a lake. You can use that to your advantage by paying attention to Steep bluffs, heavy forests, etc.....

Everybody wants a simple formula for thermals but in reality thermals don't always go straight up and straight down there's far more to it than that.


I'm certainly not looking for a simple formula, just looking for others insight on how the addition of a lake thats around 94 acres in the close proximity to some rolling hill points would likely effect the thermals compared to the same terrain without the lake.


I hunt lakes a lot down south. Shade is a huge factor in a lot of cases.


would you be willing to elaborate? I'm not really sure what you mean by that. are you talking about shade on the water making the water cooler in that area? if so, how are you seeing that effect thermals?
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Re: Lake Thermals

Unread postby DaveT1963 » Sat Dec 18, 2021 1:42 pm

Brad wrote:
DaveT1963 wrote:
Brad wrote:
DaveT1963 wrote:Wind structure and shade will vastly affect thermals on a large body of water such as a lake. You can use that to your advantage by paying attention to Steep bluffs, heavy forests, etc.....

Everybody wants a simple formula for thermals but in reality thermals don't always go straight up and straight down there's far more to it than that.


I'm certainly not looking for a simple formula, just looking for others insight on how the addition of a lake thats around 94 acres in the close proximity to some rolling hill points would likely effect the thermals compared to the same terrain without the lake.


I hunt lakes a lot down south. Shade is a huge factor in a lot of cases.


would you be willing to elaborate? I'm not really sure what you mean by that. are you talking about shade on the water making the water cooler in that area? if so, how are you seeing that effect thermals?


https://youtu.be/4pBGIlX0iv4
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Re: Lake Thermals

Unread postby Brad » Sat Dec 18, 2021 2:38 pm

DaveT1963 wrote:
Brad wrote:
DaveT1963 wrote:
Brad wrote:
DaveT1963 wrote:Wind structure and shade will vastly affect thermals on a large body of water such as a lake. You can use that to your advantage by paying attention to Steep bluffs, heavy forests, etc.....

Everybody wants a simple formula for thermals but in reality thermals don't always go straight up and straight down there's far more to it than that.


I'm certainly not looking for a simple formula, just looking for others insight on how the addition of a lake thats around 94 acres in the close proximity to some rolling hill points would likely effect the thermals compared to the same terrain without the lake.


I hunt lakes a lot down south. Shade is a huge factor in a lot of cases.


would you be willing to elaborate? I'm not really sure what you mean by that. are you talking about shade on the water making the water cooler in that area? if so, how are you seeing that effect thermals?


https://youtu.be/4pBGIlX0iv4



enjoyed the video, and very informative. that's exactly what I would have expected to happen in the evening. in some ways that spot has some similarities to the one I'm referring to. have you ever hunted mornings in that area and seen how thermals are moving in the mornings? I would expect thermals to rise up the hills once the sun is hitting those hillsides. But would the thermal current likely continue to pull toward the lake in the mornings before the sunlight breaks over the horizon?
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Re: Lake Thermals

Unread postby Brad » Mon Dec 20, 2021 9:55 am

In case this helps someone who may be interested.
This morning I went to that spot I was asking about. I got exactly what I expected, which was exactly the opposite of what the weather underground wind prediction told me it would be.
The wunderground prediction was a slow 2-3 mph NW wind before shooting light, sunrise was around 7:20 am, and just after sunrise shifting to W, then SSW by 10 am.
Because the wind speed was so slow, I was expecting the thermals to be in complete control of the air current. I expected the lake to pull my milkweed toward it (as if a SW wind) until the sun hit the ground under me, which is exactly what happened. I also expected the ground to warm as the sun hit it, and then pull the milkweed up the drainage/hill (like a NNW wind) which is exactly what happened. Most people seem to shy away from hunting low due to swirling winds, but I've learned that you can predict the air flow fairly easily in the low spots if you have those very slow variable wind days.

I saw nothing until around 9am, then started seeing some does off in the distance, a pair of fork horns went up the point I was on to go to bed, and then... the does were getting pushed hard by a buck that wouldn't stop grunting. He was the most vocal of all of the bucks I've hear in person. I saw the 5 does he was running, but never got eyes on the buck. Unfortunately it went quiet right at that time, which was when I realized it was time for the thermals to shift,, so my wind going toward them may be what shut it down. I immediately left, since I had planned to hunt only the morning and promised I'd be home...but now I need to go back and see who the bully buck is.
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Re: Lake Thermals

Unread postby KRONIIK » Mon Dec 20, 2021 11:32 am

Brad wrote:In case this helps someone who may be interested.
This morning I went to that spot I was asking about. I got exactly what I expected, which was exactly the opposite of what the weather underground wind prediction told me it would be.
The wunderground prediction was a slow 2-3 mph NW wind before shooting light, sunrise was around 7:20 am, and just after sunrise shifting to W, then SSW by 10 am.
Because the wind speed was so slow, I was expecting the thermals to be in complete control of the air current. I expected the lake to pull my milkweed toward it (as if a SW wind) until the sun hit the ground under me, which is exactly what happened. I also expected the ground to warm as the sun hit it, and then pull the milkweed up the drainage/hill (like a NNW wind) which is exactly what happened. Most people seem to shy away from hunting low due to swirling winds, but I've learned that you can predict the air flow fairly easily in the low spots if you have those very slow variable wind days.

I saw nothing until around 9am, then started seeing some does off in the distance, a pair of fork horns went up the point I was on to go to bed, and then... the does were getting pushed hard by a buck that wouldn't stop grunting. He was the most vocal of all of the bucks I've hear in person. I saw the 5 does he was running, but never got eyes on the buck. Unfortunately it went quiet right at that time, which was when I realized it was time for the thermals to shift,, so my wind going toward them may be what shut it down. I immediately left, since I had planned to hunt only the morning and promised I'd be home...but now I need to go back and see who the bully buck is.


Unless I'm missing something (or your map isn't oriented with North at the top), it seems to me that you are operating under something of a misconception regarding wind direction terminology.
When referring to wind direction, it's commonly accepted that a North-West wind, for example, means that the wind is COMING out of the North-West, not blowing toward it!

I think perhaps that you are thinking the opposite?
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Re: Lake Thermals

Unread postby PK_ » Mon Dec 20, 2021 11:59 am

Yea a lot of people don’t understand that looking at a weather app for the predicted wind direction is like taking investment advice from a bank teller.
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Re: Lake Thermals

Unread postby headgear » Mon Dec 20, 2021 1:10 pm

I don't seem to find much thermal pull in the morning, often the rising sun pushes cool air down and everything is often still so local wind or weather might be worth looking into more than thermals. Not that they might not be there but I haven't seen any compelling pull before or right after first light. You would be better off planning for any rising thermals once the sun rises a bit. We have talked about a morning thermal pull on huge bodies of water like lake michigan before but that is a different beast.

In the evening in that kind of terrain the pull should go up the finger to the larger lake. In flatter terrain I have had larger bodies of water pull my scent in the wrong direction when I had setup closer to the smaller body of water, the deer had a good laugh at that one too as I could hear them bust me one by one. The lake pull on thermals can pull from a long ways out too. The valleys and ridge systems at the ends or around the lakes will pull in scent for miles, it kind of extends the size of the bedding area thermals in several directions, it is predictable and they setup for it. A nice way to smell all of the high ground around you from a small area.
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Re: Lake Thermals

Unread postby DaveT1963 » Tue Dec 21, 2021 1:19 am

Brad, here is another video that covers using cameras to backtrack a buck but it also covers some thermal activity on a large lake, as far as shade can effect the thermal activity. Had to break it up into two parts.

https://youtu.be/5GXzOYH3-_8

https://youtu.be/CStbCxTdKb0


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