Definition
A forecast weather chart, issued by the National Weather Service, that shows expected significant weather conditions for a specified future time period. It depicts forecast areas of IFR and marginal VFR conditions, turbulence, freezing levels, and the location of fronts and pressure systems. Low-level prognostic charts cover the surface up to 24,000 feet; high-level charts cover 24,000 to 60,000 feet.
Plain English
A weather map that predicts where the bad or important weather will be at a future time, rather than showing what is happening right now.
Context Anchor
Seen during preflight weather planning, especially when checking the larger weather picture along a route before deciding whether to go, delay, change route, or choose a different altitude.
Derivation
Prognostic comes from the Greek prognostikos, meaning 'foreknowing' or 'predicting.' The chart predicts future weather, as opposed to a depiction chart that shows current conditions.
Why Pilots Care
Helps pilots anticipate and avoid hazardous weather that could compromise safety or require rerouting.
Analogy
It is like checking a road map that marks expected construction, flooding, or closed roads before a trip. The map does not fly the airplane for you, but it helps you choose a safer route before you start.
Intuition Check
“Significant” does not just mean “noticeable” or “interesting” here. It means weather that matters to flight safety, flight planning, or aircraft handling.
Example Sentence 1
The pilot reviewed the low-level significant weather prognostic chart and saw a band of forecast IFR conditions moving into her destination by arrival time.
Example Sentence 2
The Significant Weather Prognostic Chart indicated moderate turbulence above FL180, so the crew chose a lower altitude.