Variable Visibility : A condition when the prevailing visibility is less than 3 miles (5 km) and rapidly increases and decreases by one or more reportable values during the period of observation
National Wildfire Coordinating Group (NWCG), Glossary of Wildland Fire Terminology, NWCG Program Management Unit, National Interagency Fire Center, Boise, ID, USA 2014. http://www.nwcg.gov/pms/pubs/glossary/pms205.pdf, (For Fr - Amer) {45}