Definition
Outlined areas drawn on a Significant Weather Prognostic Chart that enclose regions where precipitation is forecast to occur. The shape of each polygon shows where precipitation is expected, and symbols inside indicate the type (rain, snow, showers, thunderstorms) and whether it is continuous or intermittent.
Plain English
Shapes drawn on a forecast weather chart to show the areas where rain, snow, or other precipitation is expected, with small symbols inside telling you what kind it is.
Context Anchor
Seen when reading significant weather prognostic charts during preflight weather planning.
Derivation
A polygon is simply a closed shape with straight or curved sides. On these charts, forecasters draw a line around the area where precipitation is expected — that enclosed shape is the polygon.
Why Pilots Care
Allows pilots to identify regions of expected precipitation that may bring icing, turbulence, or reduced visibility along their route.
Analogy
It is like drawing a closed outline around the rainy part of a map. The outline helps you see the forecast area at a glance, but it is not a wall where the weather suddenly starts or stops.
Grounding Statement
On the chart, look for the closed outlined shape first, then read the symbols or labels inside it to understand what kind of precipitation is forecast there.
Intuition Check
Do not read a precipitation polygon as an exact boundary where precipitation is guaranteed everywhere inside and impossible outside. It is a forecast area showing where precipitation is expected on the chart.
Example Sentence 1
During preflight planning, she noticed a precipitation polygon covering her destination with a symbol indicating continuous rain.
Example Sentence 2
Before takeoff the pilot checked whether any precipitation polygons crossed the planned path on the prognostic chart.