Educate me on thermals

[pseman]

I have hunted for almost 20 years and although I didn't place too much emphasis on the wind for the first few years, I now try and use it to my advantage as much as possible. Sometimes this can be tricky or futile here in the south because it seems like the wind changes direction several times per hour on some days. But to the point. Until the last couple years, I had never heard anyone mention thermals and I don't know if I totally understand them, so I thought I'd ask you guys. My understanding is that thermals rise in the morning and fall in the evening. I have heard that you should try to hunt high points on the terrain in the morning and low points in the evening. Is this all there is to them? Do they increase in effect in colder weather?

What has been your experience with thermals, and are they something that I should be overly concerned about?

[ChuckC]

Cooler air is heavy and it drops down to the lowest areas..  heated air is lighter and rises.

In the am, the air is cold and drops, or goes down hill.  Sometime after the sun rises and hits the area, it heats up the air and it starts to change up, then rise.  When  depends on how soon the sun hits the area and warms up the air.

The reverse again happens in the evening, when the sun no longer directly heats the area.

This is most readily seen in the hills or mountains, but it also happens in lower areas as well.
ChuckC

[John Scifres]

The only place I count on thermals is in the big mountains.  They are very easily overridden by winds here at home, even in hilly places.  On very calm days, there is some effect.  For instance, calm, sunny days are a good time to be in a tree.  Calm cool mornings, not so much.  Still hunt the creek bottoms then.  There has to be a temperature change of some magnitude for the effect to be worthy of consideration.

[Deff]

From a practical standpoint -- what the thermals mean is:
If you are a stand hunter, you try to set up with the breeze in your face, sun at your back and wait.
When the game eventually appears  - you discover that the breeze has switched -- and away they go!
"Hunt high in the morning" seems to help a little, "Hunt Low" in the evening helps them to SEE YOU before they smell you!
 

[George D. Stout]

Thermals are not always so easy to understand.  They are fickle, here in the ridges of Bedford County, and heating/cooling is only part of the story.

Air will try to find the easiest route and may sift down a valley on minute only to turn around and rise quickly half way down.  The best way to learn about thermals is to be in the woods as much as possible to see what the air does in that area.  There are no hard fast rules.  If there is a dead calm...colder air will sink and warmer air will rise.  Throw in some varied terrain and the rules disappear.

[Doc Nock]

I'm with George.

I had dried some milkweed pod (kapock) stuff for wind testing one year.

I was down in a low land near a creek (white clay creek in Chester Co, PA)

I was 20' up a tree, near a flat some 50 yards from the creek... the ridge was not high but behind me and there was a very wide draw the creek ran in angling off to my right... slightly rising in elevation.

I turned loose one of the milkweed fluffy things...and watched it go off toward the flat at 10:00 position...20 min later, here it comes back..dodgin trees and limbs...and started past me up the hill in the 5:00 position...then veered straight up the "draw" at 3:00 position...

I shrugged.  Color me amazed when in another 15 min..here it came back down by me AGAIN...this time..it went straight down the flat at 9:00 and never veered... I saw it a few more times but dont' recall in detail each trip's direction... but that totally freaked me out...and it wasn't moving fast..just barely floating along on whatever errant and redirecting current there was, which changed constantly.

That was when I decided to start paying more attention to scent control!  

[Cory Mattson]

Thermals: In mountains - air from the valleys rises uphill during the day - say 10:00 AM to 3:00 PM - then de-thermalization occurs and it changes to the reverse - cool air rolling down hill. This has happened every day I hunted during August & September in Utah and new Mexico over a twenty year period - don't know if it happens year round or not. [Dethermalization] may not even be a real word - but this is how me and my buddies understand it.

Non Mountains: Back east in the south we have what we describe as dethermalization every day - usually 8:00 to 8:30 - the air colum will flip - and it gets 10 to 15 degrees colder - Before gradually rising in temperature for the remainder of the bright daylight portion of the day. Steady wind - although often slight - usually begins after this dethermalization period. Evenings is cools - but not as rapidly - usually a soft drop before and during sunset.
<>< <-----------------<<<<<<<<<

[JDice]

IMHO - the book "Mapping Trophy Bucks" by Brad Herndon contains a lot of good info on the wind - includng discussions on thermals. In addition to a chapter named - Mastering the Wind, A Key to Success slmost every scenario in the book includes comments on the wind.

[pseman]

Thanks for the replies fellows. I guess what I am trying to determine, is whether or not I can use thermals to my advantage in addition to the wind. Or, are they too unpredictable to use to my advantage. I assume that any wind, greater than say 5mph, will override the thermal effect, but on calm days, how much consideration should I give them?

My hunting areas contain both steep ridges and relatively flat areas. Am I over-analizing?

[Cory Mattson]

No not over-analizing.

You will have less trouble in areas that are basically flats - at least there you can factor predominant wind direction (checking the weather channel before leaving) and confirming as you walk in with a talc bottle. Whatever the currents are doing - be they Thermals or dethermals - you should be OK in a treestand - positioned down wind (large percentage of the sit). In the south (water) effects  wind draft and direction to a great degree - and it will work well for you if you get on or next to water - since it (water) tends to funnel air flow for a variety of reasons - and it is usually a little stronger and easier to read than areas back away from water. This is true of Rivers - but especially large lakes - which as you know are very common in the south.

Ridges: You must be on the very top - and at what you believe to be the down wind edge. Flats or Ridges - always get on top of your area - never down low. Sign looks good down low I know - but the deer will pick you out - stay "UP" in all cases - even just 10 feet makes a big difference in the south.
<>< <--------------<<<<<<<

[Nate Fikkert]

I know they always seem to start changing in the mountains just as you are working in on the elk you have been chasing all morning.  I have found there are a couple of hours in the morning while they are good and consistent down, and then they will get steady mid-morning.  The time frame when they are deciding whether to blow up or down is EXTREMELY frustrating.  Sometimes best to just back out and wait for them to get consistent.

Nathan

[pseman]

Alright, another question. Are thermals any more or less prevalent in lower temps? Or, is it dependent on the temperature fluxation? In other words, on a cold clear day when the temps are cold at sunrise and rapidly warm up with the sun, are the thermals more prevalent than say a cloudy day with less temperature fluxuation?

[Dave2old]

In the mountains and hills, which is all I know, you definitely can use thermals to your advantage. As George D. suggests, thermals can be fickle. Yet if there's no wind, but only thermal activity, it becomes very predictable for given areas you spend time in and learn to understand. One of my most productive (grand) stand sites here i CO is on a steep sidehill above a spring pond. The general slope is modestly steep downhill, N to S in this case. But every gully and other terrain feature deflects, sucks in, or otherwise affects the basic N-S flow, so that I can sit on this hillside all day with a consistent upslope breeze -- to me from the spring, that is, in this case E to W. Thus, I have 3/4 of my immediate hunting area wind-favorable. Without the thermals, it would often be near dead-still, leading to swirling, settling, etc. It seems that flat country would be far less predictable. In any event, it needs time spent there over the course of a season to really understand. This is good stuff -- woodsmanship. Thanks for your curiosity and I hope I didn't confuse matters. dave