Definition
A Meteorological Impact Statement (MIS) is an unscheduled weather advisory issued by the Center Weather Service Unit (CWSU) meteorologist for use by air traffic controllers and traffic management personnel. It describes weather conditions expected to occur during a four to twelve hour period that may affect the flow of air traffic within a specific Air Route Traffic Control Center (ARTCC) area of responsibility.
Plain English
A short weather heads-up written by the meteorologist who works inside an air traffic control center. It tells controllers and traffic managers what weather is coming in the next several hours that could disrupt how aircraft are routed or sequenced.
Context Anchor
Pilots may see MIS information in weather planning or air traffic flow discussions, especially when widespread weather is expected to affect routes or arrival and departure demand.
Derivation
Meteorological comes from the Greek meteoron, meaning 'something high in the air,' and is the standard term for the study of weather. Impact Statement is plain English: a statement describing the impact something will have. Together it means a written statement about how the weather is expected to affect operations.
Why Pilots Care
Helps pilots anticipate weather-related route adjustments, delays, or hazards before departure.
Intuition Check
Do not read “impact statement” as a damage report or an immediate warning. In this context, it is a planning forecast for weather expected to affect air traffic several hours ahead.
Example Sentence 1
The CWSU issued an MIS forecasting a line of thunderstorms moving across the center's airspace later that afternoon, prompting traffic managers to plan reroutes.
Example Sentence 2
An updated MIS prompted the crew to consider an alternate departure time to avoid the forecasted icing conditions.