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Dixon's Notes

6. Flying Site Weather

If you want to become more successful in your ability to fly with confidence and competence it's not only important to develop your weather model for the day and your glider management skills, it's important to start noticing what the air is doing on launch, then within the mass of air you're currently flying and then at your targeted landing area. Notice and consider whether or not the air is moving because of regional flows, localized valley/sea breezes, or from the anabatic/thermal flows. You want to make the best choices of when to launch, where to locate yourself within the air mass and then make an uneventful landing based upon your skill to make sense of the micrometeorological airmass. Monitor conditions from the moment you arrive at launch, note everything while preparing your gear. Note what was occurring on launch before and after the other pilots take-off and see what they get - if they do well catching the "right" air, you can use the model of what was occurring on launch. Knowing when to launch can make a HUGE difference in your success at getting off launch easily and then finding the air you want. Many newer pilots launch at the end of the cycle and then wonder why they get non-lifting air. Quite often the best thermal is out in front of launch which requires launching when conditions are very soft on launch, a good reason to practice light-wind launch skills. While in the air be sure to continually observe the other pilots, birds and what you are sensing of the conditions. Take advantage of that information to help you move to areas of lift. Keep an eye on the landing areas and note which direction the other pilots face when landing and that they have, in fact, landed into the wind. If there aren't easily readable wind indicators in the landing area be sure and observe your ground track as you fly nearer the ground to determine your drift and thus the wind direction.

Simple air should be easily identifiable as air movement from one source, like flying a coastal site late in the day. Complex air could include regional air flows compressing through valleys then merging with anabatic flows with a large thermal within and a microburst gust front pushing the whole area. If you want ridiculously complex air fly in rotor on top of everything else, (just kidding). Until you begin to appreciate how different flow sources work together, purposely stay well within very easy flows, or combinations of flows.

An example: Although a sea breeze coastal site seems simple they can develop glider tossing thermals. Flying a coastal ridge site midday in the Summer can be turbulent, just like most sites at midday, you must still look at your stability models.

Another example: Many evenings offer heat release conditions that may be smooth and simple, but if the pressure is dropping and the upper level temperatures drop late in the day the evening conditions can become very windy and even bumpy. Be very thoughtful in the evenings, stay out in front so that you aren't blown back if the winds increase.

Another example: Many mornings are very mellow with nice light breezes, but can become very windy with strong turbulent conditions within a minute or two towards midday. Be sure and check for an inversion that may mask the strength of upper level wind flows. As the inversion warms up it can spontaneously mix with the upper level winds and be more than you bargained for.

Another example: A dark cloud showing virga/rain some miles away may lead to a gust front. Although you don't feel any wind for the time being, it's very likely you could have what is technically called an "outflow boundary" (gust front in some books) blow through. If the cell is 15 miles away and the outflow is 30 miles per hour is will take about 30 minutes to reach you.

Another example: The pressure is high, the stability index is moderate to high. The atmosphere seems pretty stable and mellow. At some point midday, between noon and 3pm, the whole area triggers and it becomes very windy with all of the oppressed heat letting go for extremely strong conditions.

The previous articles have addressed many of the above mentioned wind sources, contact me or the association for those articles. A quick description of terms not previously defined. Anabatic flow occurs on a heated slope. Stand on a sunward facing hillside without a strong countering regional wind or thermal blocking and you'll usually find a steady upslope flow from heat rising. Thermal blocking can be felt/seen as a wind sock slows down to a stand still or has a possible "blowing down" type of appearance - the wind sock is being drafted towards a thermal in front of launch. The huge mass of thermal lifting in front of launch can actually block air flows and suck air away from a hillside. A windsock that is whipping around and/or changing intensity may indicate the influence of regional and or thermal flows effecting the anabatic flow. Valley/sea breezes are from warm air being replaced by cooler air. Stand on a warm sea cliff and you'll feel a breeze as warm air rising is fed by the cooler air over the water.

Rotor is found on the backside of an object facing the wind, not a happy place. Rotor can be found behind hills, trees and buildings. You need to know that you aren't trying to launch, fly or land in rotor. Your upper level model should help you determine this as well as your observance of valley flows and gust fronts. You need to make sure the thermal strength is within your abilities, so do your stability models, look at the pressure and monitor the gust differentials on launch. You'll notice that large mountain sites can have booming thermals with light conditions on launch. Small hills may be more manageable in stronger cycles, but be sure that the gust differentials, how fast the gusts increase/decrease in a few seconds, aren't beyond your skill. As you spend more time ground handling in different conditions you'll become more aware of how gusts and top wind speeds put demands on your skill. In general it's best for recreational pilots to restrict themselves to winds under 15mph, but if you're flying in the mountains you need to restrict yourself to winds under 8mph, or less. Recreational pilots should restrict themselves to gust differentials of no more than a 5 mile per hour change in less than 5 seconds. Take the time to actually monitor these winds with a good wind meter. If you get in the air and don't like the conditions, make sure you know what was going on and make notes to yourself so you can avoid those conditions in the future. Obviously make notes about the atmosphere you like as well.

All in all, it's best to fly in pure base wind without heat, or within pure heat without a base wind.

If you don't develop your observational skills you're not training an important aspect to your flying success. REMEMBER, this sport is unlike anything you've ever done before, you need to learn a whole new set of rules - watch, listen and read.