1. A dense fog that forms in mountain valleys, especially in the Sierra Nevada, characterized by ice crystals and extreme cold.
Usage: regional; chiefly Western U.S.; plural form; singular is pogonip

Examples

• The pogonips rolled into the valley during the winter night, reducing visibility to nearly zero.
• Travelers in the Sierra Nevada had to be cautious of sudden pogonips that could trap them in dangerous conditions.
• The pogonips formed when cold air met moisture in the mountain passes.
• Local residents were familiar with the hazards of pogonips during the coldest months.