photo #5006313

It often rains in the region around Aurlandsfjord in the south-west of Norway. According to Harold Pskowski (Cloud Appreciation Society Member 61,122), the area gets rain on about 250 days in the year. On one particularly soggy day, Harold saw Cumulonimbus clouds casting such dense showers that the whole valley appeared to be shrouded in mist. Low shreds of Stratus cloud known as pannus took a ragged form in the rain-drenched air. Torn-looking patches of Stratus are known more generally as Stratus fractus, and some seemed to be billowing from the steep mountainside.When it forms against the terrain like this, Stratus fractus can also be described as a banner cloud. The wind blowing stiffly over the steep mountain peak results in a low-pressure region on its lee side. The low pressure sucks moist air up from the valley below, drawing the moisture up the slopes. When the air is as saturated as it was this day, just the slight cooling as it rises is enough for it to form droplets that appear as a cloudy banner fluttering from the mountaintop. Stratus fractus shreds like this, and the dark patches of pannus swirling overhead, are considered portents for forthcoming downpours. But we assume Harold was not handing out prizes on this particular day to any weather detectives predicting rain was on its way.