A SIGWX chart (Significant Weather Chart) is a graphical weather forecast that highlights areas of serious aviation hazards, including turbulence, icing, thunderstorms, and low visibility. Pilots and dispatchers use it to identify where dangerous weather exists and at which altitudes.
How It Works#
SIGWX charts cover specific altitude bands. The low-level chart covers surface to FL240 (roughly 24,000 feet). The mid- and high-level charts cover FL250 to FL630, making them the primary tool for jet route planning.
Meteorologists draw these charts using forecast data from numerical weather models, rawinsonde (weather balloon) soundings, and pilot reports (PIREPs). The result is a snapshot of expected significant weather at a specific valid time, typically 12 or 24 hours ahead.
Each chart uses standard ICAO symbols to mark hazards. Thunderstorm symbols show convective activity. Hatched areas mark moderate or severe turbulence. Icing regions appear as outlined zones with severity labels. Tropopause heights are noted in boxes, helping pilots understand where jet stream turbulence is most likely.
Frontal boundaries are also plotted. Cold fronts, warm fronts, and occluded fronts often coincide with the most intense hazard zones on the chart. Understanding where fronts sit helps a pilot predict where icing and turbulence layers begin and end vertically.
Example in Aviation#
A dispatcher planning a transatlantic flight at FL380 pulls up the high-level SIGWX chart for the North Atlantic. The chart shows a large area of severe turbulence near a jet stream trough over the mid-Atlantic, marked between FL350 and FL410. A cluster of CB (cumulonimbus) symbols indicates embedded thunderstorms along a cold front pushing southeast.
The crew uses this information to request a routing that stays south of the frontal boundary. They also brief the cabin crew on expected turbulence and plan a cruise altitude of FL360, just below the most intense layer.
Why It Matters#
SIGWX charts give pilots a broad strategic view of weather hazards before departure. Unlike a radar image, which shows current precipitation, a SIGWX chart shows forecast conditions across an entire region, often across an ocean where real-time data is sparse.
Misreading or skipping the SIGWX chart can put an aircraft into severe turbulence, structural icing, or embedded convection with little warning. For student pilots, learning to read these charts builds the weather pattern recognition that supports safe go/no-go decisions throughout a flying career.
Key Takeaways#
- SIGWX charts forecast hazards such as turbulence, icing, and thunderstorms across defined altitude bands.
- High-level charts cover FL250 to FL630 and are critical for jet operations.
- Standard ICAO symbols allow consistent interpretation across different countries and operators.
- Frontal zones on the chart mark where vertical weather hazards are most concentrated.
- Always pair the SIGWX chart with PIREPs and radar for a complete weather picture.