The winds aloft are calculated from measurements taken at winds aloft reporting stations located throughout each state. For each reported altitude you want to get wind direction, speed and temperature. The reported altitudes are 3,000 ft, 6,000 ft, 9,000 ft, 12,000 ft, 18,000 ft. Our FAA imposed ceiling is 18,000 feet, so there is little need to col- lect data above that level. If you are talking to a flight briefer, you will need to know which altitudes and the time frame you want the information for. If you obtain the data off the internet, you will need to understand the format in which it is presented. If the winds aloft within a few thousand feet of the ground are high, the surface winds may in- crease at some point during the day. You should be absolutely certain they will not in- crease to unsafe levels quickly and unexpectedly. Like the surface winds, if the winds aloft look too strong during the times you want to fly, there is no need to look further into the weather for that day.
You can fly in higher winds aloft than surface winds, so long as there are no obstacles such as large mountains, or the winds aren’t so strong they threaten to push you into undesirable territory. Generally winds near or above your trim speed are to be avoided. Depending on the thermal strength for the day, winds aloft may “shred” the soft outer edges of the thermals, leaving sharp edged and unpleasant thermal cores.
When flying in the mountains, keep in mind the altitude and direction of the winds so as not to launch or fly into turbulence (rotor) on the lee side (see Section 8 - The Lee and Rotor). If you you don’t know what the winds aloft are doing, the winds you see at launch may be misleading. This is one of those circumstances where col- lected weather data and visual observation can contradict and fool you into launching in dangerous conditions.
Some sites, under the right conditions, will do what is called “thermal blocking” where there is enough heat and thermal activity coming off the ground to block out a wind that is blowing from the wrong direction. These can be great conditions, but you should be aware of the prevailing winds aloft, and that the conditions may change quick- ly. At some point during the day, there will no longer be enough heating, or the winds aloft overpower the heat. Conditions can change very quickly, and you should be pre- pared to handle them or be out of the air before they change.
When collecting winds aloft data be sure to collect the temperatures at the re- ported altitudes. This will help you later when figuring out what the thermal potential for the day will be.