Is it a coincidence that I saw a stunning "mackerel sky" tonight which also signifies a change in weather, this quote sounds quite apt "Small, white and fluffy cirrocumulus clouds typically consist of ice crystals and form at altitudes around 6,000 to 10,000m (18,000 t o 30,000ft). They often form well ahead of depressions and their associated fronts. Mackerel skies and mares' tails describe forms of cirrocumulus and twisted sheaves of cirrus respectively implying strong high-level winds."