Thermal Wave

Editors Note:  This article discusses flight near clouds.  Check cloud clearance requirements in your country and personal minimums before attempting.

Thermal wave or shear wave as it’s commonly known as is quite reliable.  They can form over an extensive area, over a single cumulus, or in the blue.  The basics on how they form, they simply need a change of wind direction or a change in speed at or near the inversion.  You can commonly and regularly find them when the wind increases markedly in speed and with a change of wind direction of 60 degrees or more, with a strong inversion.

So how do we enter thermal or shear wave?  The key is to climb as high as possible in the first instance.  Under a cloud, then all the way to the base.  If it’s in the blue, try to get as high as possible, then a little bit higher(!).  Then as you approach cloud base, start increasing your speed within the thermal while maintaining height – usually to at least 80kts or above is best.  Then fly from that position to the edge of the cloud directly into the wind at that height.  What must you remember? Two things, the wind at altitude is often different from the wind at ground level and that of the wind near cloudbase, and LOOKOUT LOOKOUT LOOKOUT for other gliders.

The biggest difficulty of getting into the wave is to get this wind direction correct! Many attempts may be needed, so adjust your direction in small variations each time.

If there is a second cumulus upwind with good spacing, then this will give a good indication of the correct direction, it may even be in some unlikely directions at times, so keep a sharp lookout.  This can lead to some strong wave, because the entry shear wave cloud is like the secondary wave bar, head to the bigger cloud upwind and you may be rewarded with the primary!

If a cumulus cloud has a slope to it on the leading edge and the rear of the cloud looks regular, then this is a likely direction to fly in too.  This is what I usually first look for as I’m climbing up.  Using SkySight too in your preflight preparation can also be a great help in starting to think about whether it’s obtainable that particular day or not.  Simply select the area in question with the ‘Point SkewT’ option, it will bring up the following graph.  You can see that there is a strong inversion.  The blue line indicates the wind speed, it’s changing (increasing) rapidly near the base.  The wind arrows show the direction of the wind,  use this as your first plan on what direction to point the glider when you get to base, then adjust it when you identify the visual cues.

Then, as you exit the cloud at base, into wind and with the speed you’ve built up, simply use the inertia of the glider to pull up above the cloud base.  Pull up smoothly and to that of the min-sink of the glider, the reason, wave is usually weak down low.  What does the wave feel like? Extremely smooth, like the glider is on rails!

Banner photo by Brian Condie

 Adam Woolley was born into the gliding world, being the 3rd generation in his family. Going solo at 15, his thirst for efficiency in soaring flight & quest for a world championship title to his name has never wavered. One big passion is sharing his experiences & joy with other glider pilots all around the world. Adam is an airline pilot in Japan on the B767 & spends his off time chasing summer around the globe. He has now won 7 national Championships & represented Australia at 5 WGC's & 1 EGC.