Hi Robert @M0RWX,
Judging by the cloud in the cairn picture, you could well have been on the front edge of a long trailing cold front coming in off the Atlantic. The sharp cloud boundary and the hail/graupel on the ground are classic indicators of unstable air in a passing front, especially if it was relatively mild at ground level.
If there was active convection, electrostatic buildup would certainly be possible on high ground - If so, it probably wasn’t the best moment to have antennas up and operating!
I learnt my lesson on Ben Buie
