Sport Pilot Talk

hink · Joined: 17 Jan 2012 Posts: 17 Location: Canton, GA

How do you figure wind direction and speed for a altitude in between reported altitudes?

Example:

If winds at 3,000ft are 120 at 21kts and at 6,000ft are 180 at 14kts, what would it be at 4,500ft?

jnmeade · Joined: 30 Nov 2010 Posts: 144 Location: Iowa

The easy answer is that you interpolate. In your example, the winds at 4500 would be 150 at 17.5 knots. Interpolation works well in a perfect world. It is typical but not a lock that winds increase with altitude up to a point, so I'd be cautious about the readings in your example. Further, that is a pretty good shift in direction although not out of reason.
For those reasons, in this example, I'd be looking to the bigger picture. What are the winds and weather at other weather stations? It might be a cold front is moving through and the two altitudes are in different parts of the front. See this graphic.
http://www.crh.noaa.gov/lmk/soo/docu/basicwx.php
Another source is a skew-t if you are close to a balloon launching weather station. The skew-t shows altitudes other than those depicted by the AWS.
http://weather.unisys.com/upper_air/skew/
The FSS will give you interpolated winds. I do not know what programs they use to arrive at them.

drseti · Joined: 28 Nov 2009 Posts: 1390 Location: Lock Haven PA

jnmeade wrote: The skew-t shows altitudes other than those depicted by the AWS.
http://weather.unisys.com/upper_air/skew/

That link is a great resource. Thanks for posting it!

Quote: The FSS will give you interpolated winds. I do not know what programs they use to arrive at them.

Programs? I thought they just guessed. :wink:

hink · Joined: 17 Jan 2012 Posts: 17 Location: Canton, GA

jnmeade wrote: The easy answer is that you interpolate. In your example, the winds at 4500 would be 150 at 17.5 knots. Interpolation works well in a perfect world. It is typical but not a lock that winds increase with altitude up to a point, so I'd be cautious about the readings in your example. Further, that is a pretty good shift in direction although not out of reason.
For those reasons, in this example, I'd be looking to the bigger picture. What are the winds and weather at other weather stations? It might be a cold front is moving through and the two altitudes are in different parts of the front. See this graphic.
http://www.crh.noaa.gov/lmk/soo/docu/basicwx.php
Another source is a skew-t if you are close to a balloon launching weather station. The skew-t shows altitudes other than those depicted by the AWS.
http://weather.unisys.com/upper_air/skew/
The FSS will give you interpolated winds. I do not know what programs they use to arrive at them.

Interpolation is what I assumed, but it seems that there may be a more finite line where the shift takes place. Those were ATL centers numbers from this morning. I guess you fly your WCA based on interpolated numbers and adjust if necessary? I'm getting ready for my first dual x-country and it seems like a handful to be on the E6B, checking landmarks, and flying all at the same time.

drseti · Joined: 28 Nov 2009 Posts: 1390 Location: Lock Haven PA

hink wrote: it seems like a handful to be on the E6B, checking landmarks, and flying all at the same time.

It is a handful. Multitasking always is. Just remember that your brain has two frontal lobes. You need (consciously or unconsciously) to assign one of them to flying the airplane. The other frontal lobe has to be able to shift between navigation, communication, chart work, E6B computations, monitoring time and fuel, and everything else. Fortunately, with experience, this allocation of neural resources will become automatic.

designrs · Joined: 23 Sep 2009 Posts: 144

ForeFlight on iPad!!!

:o

jnmeade · Joined: 30 Nov 2010 Posts: 144 Location: Iowa

Interpolating is what you will do when planning your trip to see what your times and fuel burn will likely be. After you get in the air, you fly according to reality and you can check the WCA against the forecast numbers if you wish.
The key to staying on top of things is to keep your brain ahead of the airplane. Have a good idea of what things you are doing at various times and places as you fly. If things don't go according to plan make sure that you prioritize the tasks so the important ones are done first.
Sometimes if you are too busy to do something but there is not a problem, you can skip it but be sure to catch up at the next checkpoint or opportunity.
If you find as you fly that the WCA was markedly different than you planned, you may have to revisit plans such as fuel or time usage to be sure you are still OK.