They crisscross our skies on nearly a daily basis, sometimes lasting only seconds and other times expanding into widespread clouds. What are contrails, how do they form and what's behind their behaviour?
3 Day Pollen Outlook
Updated: Friday, April 24, 2015, 7:00 AM
|Low 0-20 grains/m³||Moderate 21-80 grains/m³||High 80+ grains/m³|