wind's creation & influences
Before observing the details, let’s quickly review how wind is created & influenced. Remember, air is set in motion when Mother Nature tries stabilizing regions of excess with regions of deficit. This results in air moving from high to low pressure systems in attempts to equalize everything. Basically, when pressures change, air starts moving.
There are 4-core influences affecting winds strength, direction and stability. Taking sole responsibility as winds accelerating & decelerating forces, they are controlled by the everyday natural Laws of Motion developed by Sir Isaac Newton. They include: 1-Uneven heating, 2- the Earth’s rotation, 3-Centripetal acceleration, 4 - Surface Friction. For more knowledge on wind’s creators and influencers, see Wind Part I (Kiteworld #30 page 120) and Wind Part II (Kiteworld #31 page 118), or read it online @ www.catchsomeair.us
winds three factors
Wind is typically described by two characteristics: wind speed and direction. But I’m astonished to continuously meet kiters who neglect the gust factor when judging how “epic” a potential session might be. Let’s take a look at each of these and why they’re important
1 Speed Wind speed is the velocity attained by a mass of air traveling horizontally through the atmosphere. It’s often measured with an anemometer in kilometers per hour (kmph), miles per hour (mph), knots, or meters per second (mps). Known as kite fuel, knowing speed determines your kite size, boosting capacity, relaunchability and water conditions.
2 Direction Wind direction is measured as the direction from where a wind comes from. For example, a southerly wind comes from the south and blows to the north. Direction is measured by an instrument called a wind vane, and is usually attached to an anemometer. Both instruments are positioned in the atmospheric environment at a standard distance of 10 meters above ground. Direction dictates Winds are named according to the compass direction of their source. Thus, a wind from the north blowing toward the south is called a northerly wind. The above illustration describes the sixteen principal bearings of wind direction. Most meterological observations report wind direction using these. And, here’s four very useful terms to know:
- Veering Wind A wind shift in a CW direction with height, or a wind shift at a particular level in which over time the wind shifts in a CW direction (ie. S winds shift to SW).
- Backing Wind Wind that shifts in a CCW direction with height, or a wind at a particular level which over time shifts in a CCW direction. (ie. E winds become NE).
- Zonal Flow A large scale wind flow that is fairly parallel to lines of latitude (W to E or E to W).
- Prevailing Wind The dominate wind direction at a location for a particular season (some northerly component in the colder season and more southerly in the warmer months).
3 Change Factor The third, often overlooked, component for kiters is a wind’s change factor. Just as there are no straight lines in Mother Nature, nor is there a perfectly steady wind. Both a wind’s speed and direction fluctuate continuously. When movements are slight, we have steady winds. Gust factor tells us how much change in a wind speed there is in a small time period, usually from 1-5 minutes.
When speeds are varying more than 5kts and/or direction is changing more than 22degrees, winds are variable and you’ll likely be adjusting your power frequently. Change factor is really important because when wind speeds start varying more than 10kts and/or direction varies more than 40degrees , your safety becomes compromised. No matter what you may have heard, there is not a modern day kite that makes riding in these erratically unstable winds easy or safe.
what's happening now!
Every kiter should own a handheld wind meter (mini anemometer) as their first source of accurate localized wind measurements (see www.catchsomeair.us for a nice selection). However, wind meters only measure surface winds were you are standing. They are only indicators for what you’re kite will experience. Visual observations are a critical partner to the wind meter in understanding what winds are doing before launching your kite.
The Beaufort Scale You can zone in on wind speed, and to some extent gust factor, by using the Beaufort wind scale. This descriptive scale was originally developed by Admiral Beaufort of the British Navy in the early 17th century. This scale helps mariners, and kiters, determine wind speed and fluctuations from simple observations. Overtime, the Beaufort system has been standardized for both land and water use. You simply look for specific effects of the wind on the environment to determine speed.
For most kiters, Forces 3 – 6 offer the most enjoyable kiting conditions. When making your observations, if you notice the surroundings fluctuate from one force to another, there’s likely a 5kt gust factor. If you notice the surroundings vary up or down two or more forces, you have a 10kt gust factor. This is when you should consider keeping your kite grounded.
vegetative wind indicators
Trees growing in an area of high winds are often permanently deformed. Severe deformation, such as when the tree trunk is bent away from the prevailing wind direction, occurs at wind speeds of 12 – 16kts. However, "brushing" or "flagging" can be seen in a tree exposed to average speeds as low as 8 to 10 mph which prevail from one dominant direction. An examination of the vegetation in a launch area can be a rough indicator of typical wind strengths and directions there.
We see brushing commonly in deciduous trees, like maple, oak and elm, where the branches and twigs bend downward like the fur of a pelt that has been brushed in one direction. Flagging is common in coniferous trees, like pine and spruce. It is indicated by branches that stream downwind and by short or missing upwind branches.
Deformation absence does not necessarily imply winds are weak. Some tree species are more sensitive to the wind than others. Trees within a continuous forest, for example, are too sheltered, and strong winds may blow from more than one major direction. Therefore, use tree deformation only as a rough guide and not as a primary tool in selecting a kite spot.
Flexible trees such as weeping willows are good for lighter wind conditions. Trees with stronger, less flexible branches sway during moderate to strong winds. Once wind reaches the strong to gale force category, damage to trees starts occurring. You’ll notice broken twigs, branches and removal of leaves. The Beaufort scale incorporates these measurement techniques and other effects into certain ranges of wind strength estimates.
Lastly, within dense vegetation, such as a forest or an orchard, a new effective ground level is established at approximately the height where the branches of adjacent trees touch. Below this level there is little wind. In a dense cornfield, this height would be the average corn height. In a forest, it would be the average height of the tree canopy, and so on. When observing wind speeds, all heights above the effective ground level should be considered.
Wind can raise dust and other light objects and therefore following, this movement is yet another technique that can help you estimate the strength and direction of the wind. It also can reveal eddies created by objects as wind flows around them. The same technique applies for blowing snow but this normally requires higher wind speeds.
When on the water, it’s possible to see wind’s surface flow based on changes in water texture. Relatively stronger winds will disturb water’s surface causing ripples. This region of ripples is usually darker in texture and can be observed moving as the wind progresses. Therefore, if this region, known as a wind line, passes over your riding area, you will experience stronger winds. This technique is widely used by sailors. Wind can also create waves with heights that vary according to the wind speed.
Audible Indicators Wind can also create sound. Wind passing around an object causes vibrations of that object that in turn creates a sound, normally a hissing or howling sound. We tend to perceive wind strengths based on certain sounds but mainly because we have really associated these sounds with the wind effects on objects.
from observing to riding
The moral of all this scientific kiter craziness: observing and understanding what winds are doing before you launch is critical. Because winds affect everything around them, they make it possible for foretelling your kiting session. The following breiefly explains a few key expectations you can make once you understand what the wind is doing. Knowing these can make or break your next session. Studying them will help prepare you for Forecasting Winds.
- White caps indicate both speed & direction White caps start around 12knots. The larger and more frequent they are, the stronger the wind. You can also tell the change factor by watching how frequent they shift direction & increase/decrease in number.
- When direction is shifting This is usually means a frontal system is approaching and that there will be a pressure change (i.e. a rising sea breeze or oncoming thunderstorm).
- Steady winds typically show little change in present weather, but they can also be an indicator to approaching precipitation (depending upon the direction and barometric pressure trend).
- Decreasing winds usually suggests current conditions will continue.
- Wind speeds increase typically during daylight hours and decrease at sunset.
- A Nighttime OR sunrise wind that’s steady or increasing typically means weather is soon going to change drastically.
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