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  1. #1
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    Lets talk about Thermal Winds

    I hear that early in the morning and in the evenings, the thermal winds can bust you.

    What exactly are they? Are they that important to pay attention to?

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    Thermals are another form of air movement. Like wind that can really come from almost any direction at a given time , thermals basically run up or down slope. I guess the best way to describe it is HOT air is LESS dense "lighter" so it rises and COLD air is MORE dense "heavier" so it sinks. Hunting in mountainous country "typically" the thermals "air movement" will run upslope as the day gets warmer and then downslope as the temp cools.

    This is just a basic description but hope it helps...

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    Packer pretty much laid it out as simple as it can be. This is why we go and hike up hill as far as we can in the early mornings. Then hunt down hill through the day. It allows us two advantages. One we can see farther with elevation, and two, we can typically hunt with the wind in our face vs at our backs on the way down towards our target.

    Mountain areas though have very rugged terrain and this adds a third card to the deck though. The winds are disturbed from a smooth flow like it would be over an airplane wing. This rough texture of the mountain with jts bowels, ridges, trees etc causes eddies. Just like the ones you see in a river around rocks and boulders.

    The wind swirls and that can make it more difficult to work the wind in some areas and times of day. Early am before the sun rises and after it sets are typically the calmest times.

    To best show the effect of thermal winds, the heat of the sun hits the earth within 12 minutes of it leaving the sun. Wake up early before the sun rises and go out in the cool crisp calm morning air. Stand in an open meadow or pasture and wait for the sun to peek over the horizon. Within 12 minutes of it doing so you will notice, the calm air no longer stays calm, but begins to blow...and it races away from the sun at first. This is thermal wind current. All wind is created from uneven heating and cooling of the earths surface, and this is the best example to see it happening first hand.
    I hunt because......

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    Thermals are thermals, and wind is wind. Thermals are going down for the morning hunt till 8-9 depending on where you're at. In 40+ years I've never seen it going up at o dark 30 when I start my morning hunt. I always hunt up in the morning or burn a draw and swing around if I have to start on top.

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    "Local Wind Circulations
    Mountain-Valley Breeze
    A similar situation can occur on a mountain. Most of the time the winds blow in the valley. Valley winds during the daytime would blow slowly up the mountain (Fig. 4.33) as the side of the mountain was heated causing rising motion. In the early morning or night, winds would blow down the mountains as the radiational effect of the sun disappeared. The mountain wind was a strong drainage wind caused by cool and dense air flowing down the mountain. The piling of the air at the base of the mountain sometimes produced strange effects such as pulsating winds. (Chapter 11, Whiteman)

    Click image for larger version. 

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    Fig. 4.33a Rapid heating of the mountainsides by the sun causes the air to rise and produces a valley breeze during the day.

    Click image for larger version. 

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    Fig 4.33b Cooling of the mountainsides causes a cold dense drainage flow into the valley at night, called a mountain breeze."

    This information is from my Iowa State M.S. Agronomy class from last semester. Basically, cold air is more dense than warm air, so cool air sinks and warm air rises. Wapiti is right that it takes time for the thermals to change. The sun has to heat the earth and air up in order to warm the air and switch the thermals to start heading up the mountain. There are also horizontal movements of air from wind. Thermals move vertically and wind moves horizontally. The pulsating winds referred to in the quote are from a very cold night where lots of air piled on the bottom of the mountain that ends up acting like a lake. When the winds pile up enough, it "breaks over the dam" and rushes down the valley. When it rushes down the valley, the speeds vary, causing it to feel as if the winds are pulsating. Like wolftalon stated, anything in the path of the wind will cause it to deflect, causing swirling winds or a misdirection of wind from the primary movement of the wind that day. As we all know... those deflections and swirls have ruined a lot of hunts.
    Now therefore, please take your weapons, your quiver and your bow, and go out to the field and hunt game for me.
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    This is a cool topic and something I too would like to understand better. I was actually thinking of starting this topic so I'm really glad to see it up now.

    I understand the science of thermals but how to hunt smart using the thermals properly is something I want to understand better.

    As far as the direction of the thermals, if you are hunting a cool north face, my understanding is the thermal will often continue to move downhill until say 9 or 10 am, then uphill during the heat of the day, then down hill again in the last hour or two of daylight. If there are prevailing winds, or swirling winds they can easily overpower the thermals.

    In an area I will likely be hunting this fall, the elk feed in the lower elevation around 8000 feet. There is an access trail I have been told to hunt that runs basically at a constant elevation 8500 foot elevation (perpendicular to the slope) along some benches, around the ridges and into the draws, crossing three ridges. In the draws, above the trail, there are numerous ponds and wallows just above the trail that the elk will hit during the day (this is a rut muzzleloader hunt). In the morning, the elk will move from their feeding area below the timber (around 8000 feet) and up to their bedding area in the timber (around 9000 feet) crossing the access trail (8500 feet). With the thermals running downhill until around 9 or 10 am, how do should I intercept these elk?

    Second if I want to sit the wallows, the thermals will typically switch mid morning moving uphill into the bedding areas.

    Any strategies for me?
    Grand Slam #1005 + 2: Dall (1986 Yukon), Fannin/Stone (1987 Yukon), Bighorn (1988 Colorado Unit S-26), Stone (1995 British Columbia), Desert (2001 Nevada Unit 161), Bighorn (2009 Wyoming Unit 5)

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    Well dont think of thermals as a north south east west thing. Air is either high pressure or low pressure.

    cold air is the typical of high pressure. Cold is of course relative, as its a comparrison of the temperature of the air surrounding the air mass we are considering. Cold air, is dense, and falls, or high pressure if you will. Pressing against the earth as it falls. The high pressure also rotates clockwise and as the cooler air contacts the surface it spreads outwards. So clockwise rotation of the airmass or cells, downward flow, and outward. High pressure tries to move toward low pressure cells.

    Low pressure cells are typically warm air masses. They are going to rise as they are lighter and less dense. They move in a cyclonic rotation, or counter clockwise and inward flow. Think tornado.

    just like a screw, righty tighty left loosy.

    I had to learn alot about weather and how it works as a pilot. The knowledge comes in handy when hunting too!
    I hunt because......

  8. #8
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    Those were some great explanations. I am slowly learning more about hunting in the mountains.

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    All I know is the wind blows like hell up the Deschutes river in the morning and down in the evening. This makes for exciting fly fishing. I have only stuck a hook in face once. Good thing it was barbless. I noticed over the years if the wind didn't blow in the evening, it was because a weather system was moving in. As expected, you would wake up to overcast or even light rain the next day.

    I would conclude that the higher you are, the less the impact. The further you are down the canyons, the more the funnel effect starts to kick in.

    What makes it hard to handle is when you combine local thermals with "wind" created by the larger scale thermals. An example of this can be seen in Oregon's columbia river gorge. You are not really changing altitude. But the wind blows up and down the Columbia gorge depending on the weather systems nearby.

    These are my observations, but I too would really like to be able understand and predict winds better.

  10. #10
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    Are thermals an every day occurrence throughout the year or do they happen more at one time of the year versus the other?

 

 

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