Ever been out on the dance floor cutting a rug and have the fiddlers suddenly change their tune? It can be awkward, especially in the midst of a do-si-do.
We were in wave about a mile above cloud when we noticed the cloud thickening and the good lift weakening even as it crept forward, upwind… That didn’t seem to make sense. Clouds ordinarily shrink when lift weakens, and waves that migrate almost always move downwind. These anomalies made us look closer and think more carefully, which is when it got interesting.
Before, there’d been just one layer of broken cloud between us and the earth, and ample avenues for descent. But while pointing out that a second layer had formed above it I spied a third layer hiding under… a more greenish shade, the signature of GROUND FOG!
At once the sole mission was to find how quickly we could get DOWN. Even diving with full spoilers, we had several huge spirals to better observe and understand what was happening. Our wave wind had been from the south, but while we faced mostly that direction very different weather was encroaching from behind us. As our local wave flattened, converging winds on a larger scale generated broad uplift almost everywhere, clouds growing into a thickened mass. Safe escape routes were vanishing by the moment.
We had to fly away some distance for a neat passage back to the airport, and got there barely in time. Fog was rolling up the the runway before we finished securing our bird.
I’ve now experienced this same kind of rapid sea change at three different soaring sites, so the question is not if, but where and when it will occur again .…