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Summary

This note focuses on the aspects of meteorology that need to be considered when making decisions to get the best score in a competition task. It assumes a general level of knowledge and experience from cross country flying. The focus is on identifying whether there are one or more air masses in the task area and for each airmass the best height range and time of day to fly in. To obtain this picture of conditions a series of questions are posed with ideas on how to find the answers from the meteorological data that is usually available. In this way a competitor has a checklist of information to use when planning and making decisions during a flight: max. cloudbase, change in cloud cover (including blue days and spreadout), lift strengths, inversions, wave effects, and sea breezes. Skew -T soundings and forecasts are used with tutorial references provided for the reader. These charts are shown to be useful in the understanding of an air mass. Given that scores are weighted to going early, the meteorological conditions in which a late start might be a better option are considered. Where there is a choice of air masses to fly in, comparisons are made to help decide how much off track it is worth going in order to make use of the better air.

References

[1] http://s214580749.websitehome.co.uk/tutorials/tut-various/day-planning/day-planning.html
[2] http://twister.sbs.ohio-state.edu/helpdocs/skew_T_help.html
[3] http://www.itadvice.co.uk/weatherjack/tut-soundings/tut-snds-01.html
[4] http://aviationweather.gov/general/pubs/front/docs/feb-04.pdf
[5] http://www.scalialab.com/classpages/304/Skew%20T%20Log%20P%20Diagrams.ppt

Introduction

Competition requires flying fast with an early finish or best time round the course to win. To achieve this we want to find the best lift as early as possible in the day. We look to the local area weather forecast for the information we need to predict the time and place to fly for best score.

Assuming a good understanding of meteorology for cross country flying, this note aims to identify the aspects of local weather conditions that pilots use in competitions.

So the big questions are:

• How many air masses will we have in the task area?
• How will the lapse rate and dewpoint in each air mass change during the task?
• Is there any chance of high cloud spoiling things?
• Is there any chance of wave and will it make things better or worse?
• Will there be a sea breeze, if so where and when will it appear?

And what conditions does that give:

• What will cloudbase be (in each air mass) during the day?
• How much cloud cover will there be? / Is there any chance of spread out? If it is blue will the inversion break?
• Is it better to have a lower base and deep sucking clouds or high base and thiner non sucking clouds?

So what does the weather say about how should I fly:

• Which air mass will give me the better score?
• Do conditions favour starting later for a better score?

Conclusion

For best score we choose the route and timing through the air by looking for maximum energy in all three dimensions. Horizontally large regions are viewed here as distinguishable air masses where we may have the option to navigate through the better air. Vertically the air is viewed as a profile of lift strength with height from our knowledge of the Skew -T plot. We choose to fly in a height band around the strongest lift, and the size of the band determined by the spacing of thermals. The checklist provides a means to derive from the various forecasts a picture of the air in the task area.