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©Stefano Padovan
A day with very strong wind,clouds moving very fast.The effect is the movement of the clouds.6 pictures assembled togheter with over and under exposed for a nice HDR picture.Total time around 20 seconds,Powershot G9.
Actually my first HDR picture
©Stefano Padovan
Mammatus clouds,something very strange but easy to see in summer.It happens when there is cold air and small ice crystals from the top of huge cumulus coming vertically down to the ground,Close to the surface they find hot and humid conditions so from ice they change into vapour.A very heavy condition that usally brings heavy rain and winds.Airplane pilots totally avoid this kind of clouds.
Here some explanations:
skybrigades.com 