The signs at the summit are electrical, not meteorological. The mountain is the higher realm of consciousness, and thunder and lightning are the electrical movements running through the body as that higher state ignites. The noise of the trumpet is the spirit-breath, the inner impulse sounding harmony at the top of the climb, the prana rising through the spine into the head. This is what awakening feels like from inside: current, sound, and smoke where the ordinary mind is being consumed.
The people stood far off because the crowd of ordinary thought pulls back from the raised state rather than entering it. What frightens the outer mind is the very charge of the higher consciousness catching fire.
Mountain: the higher realm of consciousness, the raised state a person climbs into
Thunder and lightning: the electrical movements running through the body as the higher state ignites
Trumpet: the spirit-breath, the inner impulse sounding harmony at the summit of the climb