Another hot day. At about 12:30 these neat cirrocumulus stratiformis were overhead, high in the atmosphere (between 5 to 14 km or 16,000 to 45,00 ft) where upward air currents meet high cirrostratus clouds formed of ice crystals, some of which turn into supercooled water droplets. Not long afterwards they'd disappeared, or almost disappeared; just a ghostly trace of a few in small transparent patches in an otherwise blue sky.
A hot day, even at about 18:45, when these were taken. Streaks of cirrus show that there were high winds at high altitude, while clumps of cumulus mediocris and wisps of cumulus fractus moved more slowly.