Ok, I did a little more testing, and this is what I found.
The wind started at 14,000 feet, but did not reach full strength until 14,500. From there it stayed stable at 20 mph until just before 16,000 feet, where the wind started to change direction. Just above 16,000 the wind was blowing softly from the East, and reached full strength again at 16,500.
This told me what I need to know so I can avoid headwinds and pick up tailwinds.
Hope this helps.