Jan. 9, 2020: The finest outbreak of polar stratospheric clouds (PSCs) in decades is still going strong. “We witnessed a wonderful display this evening (Jan. 8th),” reports Alex Conu, who photographed the clouds drawing a crowd in Oslo, Norway:

“The cloud’s bright pastel colors looked fabulous alongside Venus in the evening sky,” he says.

Polar stratospheric clouds are rare. Normally, the stratosphere has no clouds at all. A few times each winter, however, icy clouds form when the temperature in the stratosphere drops below -85C. Such staggeringly-low temperatures are required to help sparse water molecules stick together. This winter, the clouds have been appearing daily since late December, a sign of unusually cold conditions in the stratosphere.

Stratospheric clouds are widely regarded as the most beautiful clouds on Earth. Because of their intense colors (caused by high-altitude sunlight hitting tiny ice crystals), novice sky watchers sometimes mistake the clouds for auroras. This picture from P-M Hedén of Tänndalen, Sweden, shows why:

“On Jan. 4th, the colors got so strong that the snow turned red,” marvels Hedén. “I have been seeing these crazy displays at both sunrise and sunset from my cabin in the Swedish mountains.”

Stay tuned for updates as the outbreak continues.