With Frankfurt airport closed, note the lack of vapour trails…

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That's funny…
As I looked out this morning, I noticed the deep blue sky and realized that these “white stripes” were missing.
In a way, I had gotten so used to seeing them. On the other hand, I was aware that they had gone missing.
I'd often see these lines crisscrossing, other lines fading, and some coming in with a bit of noise. The skies have been very quiet for the last few days.