We took off at 0828Z (or 1028 local time) and encountered some scattered small cumulus with bases below 1000'. On our way north we climbed though a variety of cloud types, with some fairly tall cu's reaching to about 18,000'.
We passed over a broad band of altostratus that was moving south from the German coast and reached its northern edge just east of Schwerin. The blue line in the track plot below shows the approximate location of this band. From our flight altitude of 41,000' we could nicely see the northern edge of the cloud band, and to the north of it a field of developing small cumulus. Note also the lack of cu's in the region shielded by the stratus cloud.
To investigate the stratus cloud, we successively descended to 21,000' and headed south to enter the cloud (below).
First, we aimed for the prominent cloud top that shows in the middle of the picture on the right, but when we reached it, the cloud had run out of steam, and the top was already decaying. We then looked for more promising targets and found some excellent candidates of growing cu's. We went through these clouds at 12,000' and at temperatures around -4 C. At these temperatures, the clouds consisted still of supercooled water, but a look at some of our PMS measurement probes on the wings showed a small amount of icing. The turbulence in these clouds was quite noticeable, but not enough to upset anyone's stomach. The cloud penetrations were conducted in the region outlined in red on the flight track below.
(Thanks to Pilot Steffen Gemsa for some of the pictures above!)
Below, I include the flight track and the temperature soundings from Lindenberg.