Definition
An unscheduled in-flight weather advisory issued by the Center Weather Service Unit (CWSU) at an Air Route Traffic Control Center (ARTCC) to alert pilots of existing or anticipated hazardous weather conditions within that Center's airspace. A CWA may be issued as a nowcast describing conditions occurring now, or as a short-term forecast for conditions expected within the next two hours. CWAs are valid for up to two hours and are intended to supplement, not replace, SIGMETs, AIRMETs, and Convective SIGMETs.
Plain English
A short-notice weather warning put out by the weather specialists working inside an Air Traffic Control Center, telling pilots about dangerous weather happening right now or expected within the next couple of hours in that Center's airspace.
Context Anchor
Pilots may see CWAs during weather briefings, in preflight planning products, or while working with air traffic control during instrument or en route operations.
Derivation
"Center" refers to the Air Route Traffic Control Center (ARTCC), the facility that handles enroute IFR traffic across a large region. So a Center Weather Advisory is a weather warning tied specifically to that Center's area of responsibility — not a nationwide product.
Why Pilots Care
CWAs give pilots advance notice of developing hazards so they can reroute, request altitude changes, or delay departure to maintain safety.
Intuition Check
“Center” does not mean the middle of a storm or weather area here; it means an FAA air traffic control center. “Advisory” does not mean the weather is harmless; it means the notice is information pilots use to make safe decisions.
Example Sentence 1
Center issued a CWA for severe turbulence below 12,000 feet across the western half of their airspace, so we requested a higher altitude.
Example Sentence 2
After receiving the CWA about building thunderstorms, the pilot requested a deviation to the south.