rodbailey

Winds Aloft
by Dixon White ( http://eagleparagliding.com )

This is the 3rd article in a series that will review step by step concepts concerning weather and flying pointers. If you're a new subscriber to the magazine you may want to order the previous 2 issues from the USHGA to stay on track with the flow of these articles. Get together with your local instructor and club to discuss these topics in greater detail. Be sure and expand your library of books and videos. This column will recommend certain books and videos, realize that there may be some ideas that are arguable. Practice the weather concepts daily, even when you aren't going flying. Begin to identify the trends that make for the best coastal flying, thermal conditions or exhaust heat sessions. Give your chums a call who flew on days you couldn't and see how close you can get to predicting the conditions. Be thoughtful about going to new areas and how powerful some atmospheric influences may be in contrast to your home sites. There are some sites that become unruly by 9am in August yet others that can be flown all day. Hire the local instructor to guide you when visiting new sites.

Be sure and study the actual soundings of the upper atmosphere prior to flying each day. These soundings are taken by the National Weather Service at 5pm and 5am throughout the U.S.. This information can be found through a number of websites as well as through a phone call to Flight Service (1-800-WX-BRIEF). The www.paraglide.com website has a weather section that will lead you to a number of great weather information sources. Select the "Soaring Forecast" and choose the "complete report" for your area through 18,000 feet msl. You will see a few tables and a graph. Take a look at the wind direction and strength. Direction is given in compass headings (i.e. 0 or 360 degrees is North, 180 degrees is South). The wind strength is given in knots, a knot is 15% stronger than m.p.h.. Your analysis is to determine if it is blowing too hard to fly at your local launch or if it might start blowing too hard at some point during the day. Air can layer itself horizontally throughout the atmosphere due to temperature, and thus be blowing at different intensities and directions at different altitudes. It's possible for there to be a "river" of air just a few 100 feet overhead or below your launch area that's blowing the opposite direction and more than you like.

On clear nights cool air can "puddle" up on the ground for 100's or 1000's of feet in depth. This is called an inversion. As you ascend from the ground through the lower atmosphere you will often find that the air actually gets warmer. This puddle of cool air is sitting underneath slightly warmer air and it's very possible that an uninformed pilot may not know that the winds above this layer are actually very strong. Different temperature layers of air don't mix - similar to oil and water. As the sun warms the ground the ground warms the air and the puddle of cool air warms up and mixes with the upper level "river" of air and within seconds you can find yourself in strong wind.

You will also find temperatures aloft information on the internet or through a call to Flight Service and this information helps us predict stability. We will discuss the thermal and lifted indexes in the next article.