Severe weather poses risks to life or property and requires authorities' intervention. WMO categorizes severe weather into general and localized types. Extreme weather describes unusual events at historical extremes
Black ice is a transparent coating of glaze ice on surfaces. Forms when light rain falls on roads below freezing temperature. Can occur when road surface is slick from rain and temperatures drop
METARs provide hourly weather observations at specific airports. TAFs cover 24-hour period with updates every 6 hours. MOS forecasts weather up to 72 hours ahead. SIGMETs warn about hazardous weather conditions. PIREPs are voluntary flight weather reports
Snow forms when water vapor freezes below 0°C in clouds. Snowflakes are clusters of ice crystals falling from clouds. Snow pellets form from supercooled cloud droplets falling through ice. Sleet is small ice balls formed from rain or drizzle. Hail forms when updrafts prevent graupel from falling
Supercooled water freezes on aircraft surfaces below zero temperature. Water droplets larger than 50 microns can cause significant icing. Clouds containing liquid water can create icing conditions below 0°C
Icing can be classified as light, moderate, or severe. Severe icing requires immediate heading and altitude changes. Clear ice is more dangerous than rime ice. Aircraft manuals advise avoiding moderate to severe icing conditions