Altocumulus lenticularis - known to mountain pilots and photographers as lenticular clouds - are smooth, lens-shaped formations that appear stationary over or downwind of a prominent ridge. They form when stable, moist air is forced up and over a mountain, creates a standing wave on the lee side, and condenses at the wave's crest. The cloud looks stationary because the air is constantly moving through it: moisture condenses on the upwind side of the wave and evaporates on the downwind side. At sunrise and sunset they often glow fiery orange and pink, looking for all the world like UFOs suspended over the peaks.
Inverza's detector combines SRTM terrain analysis with pressure-level atmospheric data to predict this condition with precision. It first identifies the dominant ridge within a 30 km radius of your location (requiring at least 400 m of prominence), then evaluates the wind field at 700 hPa or 500 hPa depending on ridge altitude. The cloud forms when four conditions align simultaneously: strong ridge-top wind (25+ km/h, ideally around 45 km/h), wind blowing near-perpendicular to the ridge line, a stable atmospheric layer (lapse rate below 6.5 K/km between 700 and 500 hPa), and humidity in the 55-85% sweet spot at crest altitude. Standing on the lee side adds a final bonus - that's where the wave crests condense visibly.
