Wind and Terrain

[rickp]

Anyone know of a website or reference material with detailed information on how terrain affects wind.
I'm looking for something with different terrain features .
R

[Anchor Zero Six]

I think there are too many variables to have a one size fits all formula.

I have done a considerable amount of distance shooting in high desert terrain in various weather. Will you be shooting high to low or low to high? Is the target on the sunny side of a slope? Are you on the bottom of a draw shooting upward across another gully? Is the wind constant at both positions or are there variations across the projectiles flight path? Can you see where I'm going with this?

Whats often overlooked in long range shooting is that there is alot of really boring down time ;) Some folks (myself included) enjoy the OCD aspect of it while others do not. I suggest spending some casual non shooting time honing observation skills. I do alot of hiking and make a habit of bringing a Kestrel with me to improve my skills at wind calls. Taking note of how much different types of vegitation will deflect at different wind speeds gets logged so I can later use that to judge whats happening downrange along the flight path. A wind meter will only tell you whats going on where you are at which dosnt do alot of good if the wind is obviously different at various points along the way.

With solid data you may not be able to predict what the conditions will be but you can vastly improve your ability to decipher what the terrain and elements are doing and in turn make the needed corrections.

[a0cake]

I don't have exactly what you're looking for, but I can help you a bit. The environment that I have worked in most is river valleys. I've learned quite a bit about wind patterns in these areas. If you're asking this in preparation for a trip to Afghanistan, much of the eastern AO's are river valleys. So, hopefully what I'm about to show helps you.

Below is a random deployment picture of me sitting in overwatch of a valley. I've put some marks on the picture that illustrate what I'm about to talk about.

During the day time while the sun is shining, an area of low pressure is created near the top of mountains. This attracts air from the valley floor. In addition to the prevailing winds whipping up or down the valley longways, there will be lateral winds moving up the draws that feed into the hillsides. I've used arrows on the picture to illustrate the phenomenon.

http://i.imgur.com/QFRLA.jpg

So, in the following picture, if I was taking a shot from point A to B, I would bank on seeing some degree of wind moving left to right for the shot, even though I wouldn't necessarily be able to feel it or see it from my location.

http://i.imgur.com/VvxSC.jpg


This phenomenon is fairly consistent, and for Afghan deployments the most important one. I hope this helps a bit.

Also note that at night time, the effect reverses. High pressure rather than low pressure is created at night, and wind will blow from the top of the mountains down toward the valley floor. From my position in the first picture above, I could feel the change firsthand. During the day there was a breeze in my face but at night it came from behind me.

During the day, the phenomenon is called "valley breeze." At night it's called "mountain breeze."

[rickp]

That's good stuff, thanks a0cake.

That's what I'm looking for. I know wind is very unpredictable in ways but I think it does have some behavior characteristics that some might not know, and that's what I'm looking for.

For example in your images, if the wind was coming down the valley (from the left as seen on the image) I wouldn't have thought that the wind would have moved up that draw. I would have thought it would have come over the mountain and get turbulent on the leeward side of the high ground, making it unpredictable.

Let me ask you what's creating the high pressure, the heat coming off the ground due to the sun?


I got this from another site. It has good info and some of what you're talking about.

http://www.firemodels.org/downloads/behaveplus/publications/FireWeather/pms_425_Fire_Wx_ch_06.pdf

[a0cake]

The "Landform Breezes" section of the following article explains why there is high / low pressure:

http://www.ehow.com/info_7748364_landforms-affect-weather.html

I can't get your link to work for some reason.

Also, here's another picture that better illustrates what I was talking about. I'm sure you already get it but just in case someone doesn't, I'll post the picture.

http://i.imgur.com/RrOed.jpg

The upward movement of the wind during the day has a way of funneling into long draws...even ones that don't upslope a whole lot. It's not 100% guaranteed that the wind will move into the draw like I described. Sometimes the wind situation might be more like you thought it would be. I'm not going to venture a guess on percentages but it is the way I described more often than not.

[rickp]

Link should be fixed now, give it a try.

Good stuff, thanks.

You know I'm surprised there's not more reference material on wind since it's such a huge variable when shooting.

[a0cake]

There's a USAF Special Operations Weather Team member on this site. He could probably explain the hows and whys behind wind patterns as they relate to terrain.

Long range shooters generally train to read wind on a case by case basis, using information derived on site from measurable / perceivable information.

A better understanding of traditional wind behavior around terrain from a scientific / meteorological standpoint could definitely be a useful (or at a minimum simply interesting) thing to explore.

So thanks for bringing it up.

[rickp]

I agree, I mean it's definitely not something that can be carved in stone for shooting reasons but I think it can give one a little better understanding on how both work with each other.

Again, thanks for the info.

R.

[SeriousStudent]

Rickp, this is a very good idea for a thread. I'm just getting into the precision bolt gun world, and am devouring as much useful data as I can.

A0cake, thank you for your info, and return home safely and soon.

[a0cake]

A0cake, thank you for your info, and return home safely and soon.

No problem. I agree it's a good topic and I've enjoyed talking about it. I'm actually in the US right now. Been back from the latest trip for a few months.

[SeriousStudent]

Then I hope you are busy drinking beer and oogling the serving wenches. :D

[QuietShootr]

Good stuff, A0.

A trick that helps me visualize what's happening is to think of the air as water, but taking into consideration the effects of temp and baro press that A0cake illustrated above.

The first thing is to get good at estimating the wind speed based on its effects on the vegetation and objects. Then, learn the difference between near wind and far wind, and sometimes even near and far winds in different directions. Once you get reasonably proficient at that, then you start adding in things like accounting for pressure gradients, temperature anomalies, and so on. As A0 pointed out, some of this is very AO-specific (no pun intended).

Tall buildings introduce some weird air flows that can be a real bitch to shoot around. I once got invited to help with a nuisance bird control shoot in the downtown area of a big city using suppressed .22 rifles with subsonic ammo, and I got more education about wind around tall buildings those two days than I could have PAID for anywhere. BTW - BulletFlight works just fine for doping .22s :D

[Pappabear]

Great info, great thread. Wind just plain kicks your ass. It is wind that makes a spotter an absolute necessity. Its a cool study and I am learning more on every shoot. Our location has variable wind with consistent changing direction. Its very interesting.