Warm weather thermals vs. Cold weather thermals

[Swamp Buck]

Ok, we all know about the thermals and how they can shift and change as the day warms and cools in morning and evening. My question is do you find that the thermals will change at different times due to the actual air temps?

Lets say the weather is 70's durring the day and sunny, 40's at night and clear. I have found that the thermals will change midmorning as is pretty normal about 9 AM at the latest, but due to the warm weather all day the thermals did not change much before dark making the evening hunts very hard to predict. Now lets say the weather is later in the year and you have 50's durring the day and 20's at night. Do you think that you wil have similar changes or do you suppose that the winds of change will happen a little later in the AM and a little earlier in the PM?

Will other factors affect these changing times like snow cover?

[cnelk]

Fast moving cold fronts will toss any predictable wind out the window.
And those happen frequently in the afternoons in the high country

[twinkieman]

I think what you are asking Swampbuck, is are thermals in lets say November different from September. My opinion on this is yes. Air in late fall and the winter months, in the west, has more moisture in it. Air takes longer to rise as temperatures are cooler. Does that mean they are more consistent, not really. All it takes to change airflow is a small change in temperature, a cloud passing, a thunderstorm, etc.

[MT_Nate]

This is a good discussion and puts my mind to thinking harder about this.

I've always worked thermals (thermal lift/descent) with the knowledge that speed and direction of thermals all depend upon two things...the difference in temperature between the high country/low country; and how fast the temperature changes occur. In your example (Sept - 70 to 40; Nov - 50 to 20), the difference in temp is 30 degrees. They should behave the same because a degree is a degree no matter what range of the spectrum it is at. The speed at which the change occurs, however, makes them very different. All of this discussion considers a perfectly clear day with no fronts/winds moving through.

I believe Twinkieman is correct in identifying that the humidity in the air plays a factor, but I'm not sure the amount of difference it might make is fully noticeable to a hunter. What IS noticeable is the angle and intensity of the sun, and the speed of warming/cooling. Without writing a technical paper on thermals, pressure gradients, and winds, I think we can agree that the smaller the difference in temperature between high and low ground, the less reliable the direction and speed. We can also agree that the ground heats up alot faster in September than November.

1. Steep thermal gradients in September mean strong thermal wind, but for shorter duration.
2. Flatter, slower thermal gradients in November mean weaker thermal wind, but for longer duration.

The air is colder/denser/wetter in November, so probably feels faster than it actually is.

[twinkieman]

This is a good discussion and puts my mind to thinking harder about this.

I've always worked thermals (thermal lift/descent) with the knowledge that speed and direction of thermals all depend upon two things...the difference in temperature between the high country/low country; and how fast the temperature changes occur. In your example (Sept - 70 to 40; Nov - 50 to 20), the difference in temp is 30 degrees. They should behave the same because a degree is a degree no matter what range of the spectrum it is at. The speed at which the change occurs, however, makes them very different. All of this discussion considers a perfectly clear day with no fronts/winds moving through.

I believe Twinkieman is correct in identifying that the humidity in the air plays a factor, but I'm not sure the amount of difference it might make is fully noticeable to a hunter. What IS noticeable is the angle and intensity of the sun, and the speed of warming/cooling. Without writing a technical paper on thermals, pressure gradients, and winds, I think we can agree that the smaller the difference in temperature between high and low ground, the less reliable the direction and speed. We can also agree that the ground heats up alot faster in September than November.

1. Steep thermal gradients in September mean strong thermal wind, but for shorter duration.
2. Flatter, slower thermal gradients in November mean weaker thermal wind, but for longer duration.

The air is colder/denser/wetter in November, so probably feels faster than it actually is.

I could agree with Mt Nate on both of these points