Glidemet

Tonnes of feedback on what was an interesting weekend, particularly Saturday.

Roughly in order of arrival:

• The first report, from Andy Miller at Keevil, also happened to be the 100th comment posted on this blog! Andy reports that a southeasterly wind is actually the best for wave off the Wiltshire hills over wave, giving flights to 3,000 ft for hours at a time. Another pilot reported wave as high as 4,000 ft there, and also encountered large directional wind shear above and below the inversion
• Mike Orme and another pilot from North Hill found lift to 2,000 ft started by cliffs to the south of the field
• Paul Fritche at Parham found wave to 3,600 ft just 500 m from the ridge crest. Paul’s post also sparked the first discussion within the comments, something I’ve been hoping for since introducing them
• Bruce Cooper found wave lift outside Dublin (somewhat outside my forecast area too, really!)
• Ray Staines at Dartmoor Gliding Society reports a two hour flight in Sunday’s easterly, in the lee of Dartmoor
• Peter Thomas fround a very little wave over Dunstable, and there was the odd thermal to be had below the low inversion
• Mike from Lasham also found a little weak thermic lift on Sunday.

Paul’s question about the closeness of the wave to the South Downs ridge gives me the opportunity to use my favourite wave picture:

This was taken during the 1950s in Owens Valley, California, when mountain waves in the Sierras were just beginning to be studied. The wind is coming from the right to the left and it is accelerating down the lee slope of the mountains, rushing across the valley floor picking up dust, and then rushing upwards on the left in the hydraulic jump, where you can see the lenticular clouds forming above the rising dust. Paul could well have been soaring a rather smaller (and less dusty!) but otherwise identical system coming off the South Downs.

The Herstmonceux sounding for Saturday shows what things were like:

The top of the picture is about 12,000 ft. As you can see, the air is very stable. Air flowing over hills would want to flow down the lee side, and then spring back up as a soarable jump, forming a lee wave.

Forecasts running up to the weekend were fine weather-wise, but I had not thought about the possibility of wave until Phil King pointed it out (thanks Phil ). I was thinking that with the southerly wind and high stability wave was unlikely—-until I thought about it some more! Phil’s post is exactly the kind of thing I want to encourage—-more discussion and critique of the forecasts. Many heads are better than one!

I was a little over-worried about stratus, but it’s easy to look very silly when having forecast clear skies all week, a day turns out to be dull and overcast. This particular high is proving to be mostly cloud-free, although stratus has now indeed formed over the eastern North Sea, southern Scandanavia, and the Denmark/northern Germany area. If the wind is from the north east, that stratus can easily blow over us, often thickening as it crosses the North Sea.

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