Showers in polar air

In the early evening of Sunday 25 July 2010, dark-based showers with a manacing look, moved slowly in north-northeasterly direction. For a short time I observed weak rotation in lowered ragged fractus clouds beneath the base. After that the shower came in from the northwest and moved slowly southeast. So direction had changed!


















I think that a convergence-line/surface trough was in my neighourhood and caused this change of movement of the shower. It is possible that a pre-existing vortice in the surface windfield became stretched in the updraft and caused the observed rotation. Perhaps the late day-time/weak instability prehibited the forming of a real funnel.











This was not the first time that showers/thunderstorms in a (modified) polar airmass showed some nice visual sights.





Here a bonus-image of the sunset of 23 July with dissipating convection (at that time the airmass was still warm and humid).