Primarily for general aviation discussion, but other aviation topics are also welcome.
By Red
Had a Bimble yesterday and again today (Tuesday/15th), as you know it has been unseasonably warm and sunny both days, yet it was smooth as silk on both flights...not a bump to be felt.
I can only remember vaguely similar conditions on a flight in the middle France a few years ago.

What makes the conditions of the past 2 days non-thermic? (I'll admit right now, I found Met the hardest subject to get my head around)

P.S. There was a noticable inversion just today but not yesterday
By Skylaunch2
Very stable airmass with not enough of a temperature to break the low inversion and trigger proper mixing and convection (needed to be closer to 30c). Therefore today weak thermals only to about 1000-1500ft at best and smooth above. Unsurprisingly with the low inversion comes poor visibility as the muck gets trapped beneath it.

Have a read about Skew-T charts and you'll enter the very interesting world of convection amongst other items, Glider Pilot's dream. One of the easiest ways to raw predict thunderstorms is using this method.

Contrary to popular belief, thermals are not subject to hot temperatures, you can get good thermals at -10c and rubbish ones with 35c, it's all about the airmass, in this case a very stable one!
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By lobstaboy
Thermic (unstable) air is relatively cool and is heated from below by the action of the sun warming the ground. Note I say relatively cool - it's the difference between the air temperature and the temperature of the layer of heated air at ground level that's important. This is often in summer, but you can get thermals in Scandinavia at quite low temperature.
Anyway just now the air is coming up from the south and is very warm when it gets here. And the heating effect of the sun is lots less now than at mid-summer so the temperature difference is much less, hence less thermal activity.

@Skylaunch2 beat me to it, but we're saying the same thing.
In the UK the best thermal days (or most bumpy) tend to be when we are in the cool air after the passage of a cold front.
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By Red
Got it I think, I was only thinking about how different surfaces heated the surrounding air made thermals and not thinking about the temperature difference needed between that air and the air above to make thermals being negated because it was incoming warm air rising the temperature more than the convective heat from the surface.
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By Charles Hunt
It's OK, I got all the bumps last week.

My skydemon vertical tracks are never particularly smooth, but this one looked like a deep cut saw with finely spaced teeth.