Wind readings at elevation or max ordinate.

Zxthinger

Shooting across valleys and other topographical features that present a drop in relative ground level has the net effect of placing your bullet higher above the disturbed layer of air and as the higher air is generally unimpeaded thus runs faster, but by how much? Is there a formuula or a rule of thumb that one can apply in he field.

SO...
Does anyone know if there exists a rule of thumb for shooting across valleys or other such similar features.

ALSO
IIRC it was stated somewhere that wind speeds quoted on weather charts and such are for 10m above ground level. You generally notice that winds speeds which are quoted on the TV weather forecast are nearly never experience at ground level when out shooting in farm land.

It is also my understanding that once winds start to exceed 7mhp then they start to flow differently having extra energy allows them to trust up and down into different layers of air. ie a gentle breeze will flow around a hill top but a stout breeze will not deviate and will flow over the top of the hill.
All these variables must be considered too

I have witnessed reduced drift when shooting across flat ground from prone to targets that are also low so as such I know that there

clivej

Get a wind meter. That will give you the correct wind speed at ground level at your present position, where the wind deviation has the most effect on the bullet.

bravestar

Wind speed at your location = science
Wind speed for the rest of the bullets trajectory = art. There are no hard and fast rules in art.

As Clive has said above, the most subscribed to belief these days is that wind at your firing position will determine where your bullet goes, with all other winds along the way modifying that trajectory to a lesser degree.

Only way to know for sure is to get and shoot while making detailed notes and carful observations.

Zxthinger

Thanks for reaffirming that wind at muzzle is weighted the most.
BTW I do have a wind meter and I use it as an when needed and over flat ground it's readings and the subsequent adjustments seem to correlate extremely good. However as stated winds over steep mountainous terrain where the bullet travels high seem to be 30-50% further off the mark and as such I have started allowing a 40% increase from that of the wind sped at the firing point and it seems to be working well at least for the few spots that frequent.

clivej

Something else to add to your theory's.

I hunt within sight of Slievenamon mountain. Sometimes I see clouds forming on the lee side of the mountain where the light wind will roll down the mountain side into cooler air. There won't be clouds on the face of Slievenamon.

So now add air density to your equation that may slow your bullet down as well.
Ah ballistics it's a love hate relationship :D

Zxthinger

Wind gradient is what I am looking for.

I worry about air density once I have wind speed sorted.

long range shooter

See on the snipertool by Thomas Haugland,he has made a rule of thumb based on own experience shooting across valleys in Norway.

https://s-media-cache-ak0.pinimg.com/736x/50/e5/38/50e538dd2a2c621b2d501f07a1b2551e.jpg

These numbers just acknowledge that wind velocity increase with elevation above ground. These numbers are not a ballistic calculation, just a simplified an indicator to build your own experience.
• Base your windcall on visual indicators and adjust your scope windage for that.
• In cases where you are shooting the bullet far over the visual indicators you used for the windcall, add some clicks on the scope.
• Where you can see the wind along the bullets trajectory DO NOT add these clicks.
• Use the first column (+2/+3) when you shoot the bullet approximately 10 meters above your visual indicator for the windcall. The last column when your «very far» above your visual indicator.
• «GAP» is used when you have a gap that will compress and blow a very strong wind across your bullet trajectory

Zxthinger

Here is the science behind the issue.

Although the calculations are vague they demonstrate a method which is acceptable to allow better understanding of higher airflows at the maximum ordinate over low terrain etc
http://es.ucsc.edu/~jnoble/wind/extrap/

Long range shooter, thanks for the link to that high quality photo. Does Thomas hangland have a blog detailing how exactly he uses the card?
I know he does YouTube vids.

Zxthinger

Found it.
http://www.thlr.no/mdb/download/pdf/THLR-Snipertool-user-manual.pdf