File:Fog, fires, and smoke near Lake Baikal, Russia (MODIS 2015-09-07).jpg

English: As autumn approaches, cooler weather brings fog to Lake Baikal, but the fires which have ravaged the region since early spring, 2015 still burn relentlessly across the landscape.

The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite captured this true-color image on August 27 as it flew across Lake Baikal. Bright white fog obscures the normally brilliant blue of the waters, and the fog also sends fingers of white creeping into nearby low valleys. Gray smoke flows across the region, crossing Lake Baikal and obscuring the northern part of the lake from view. Red hotspots mark areas where the thermal bands on the MODIS instrument detected temperatures hotter than background. When accompanied by smoke, as in this image, such hotspots mark actively burning fires.

When cold air flows over warmer water, some surface water evaporates into the cold air and saturates it, raising its relative humidity to 100 percent. The phenomenon is alternately known as evaporative fog, steam fog, and even as �steam smoke� � a term that seems particularly appropriate in such a highly smoky scene. Meteorologists define the existence of fog as visibility of less than 1 km (0.6 mi) at ground level.