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Surface Analysis Charts and Low-Level Prognostic Charts in Aviation

For pilots, weather charts are some of the most valuable tools available when preparing for a flight. Two of the most widely used resources in preflight weather planning are the Surface Analysis Chart and the Low-Level Prognostic Chart. These charts give pilots critical insights into current and forecasted weather, helping them avoid hazardous conditions and make safer decisions in the cockpit.



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Surface Analysis Charts

What They Are

The Surface Analysis Chart is a real-time representation of current weather conditions across the United States and surrounding regions. Issued every three hours by the National Weather Service (NWS), these charts provide a snapshot of the atmosphere at the surface level (sea level pressure).


Key Features of Surface Analysis Charts

  • Isobars: Lines of equal pressure, showing areas of high and low pressure. Tight spacing indicates stronger winds.

  • High (H) and Low (L) Pressure Systems: Marked with blue “H” and red “L” symbols, these influence wind patterns and weather conditions.

  • Fronts:

    • Cold Fronts (blue lines with triangles) – Bring cooler air and often thunderstorms or heavy rain.

    • Warm Fronts (red lines with semicircles) – Bring warmer air and possible widespread precipitation.

    • Stationary Fronts (alternating red semicircles and blue triangles) – Can cause prolonged periods of rain or low ceilings.

    • Occluded Fronts (purple lines with alternating semicircles and triangles) – Often bring complex weather with rain and storms.

  • Weather Observations: Includes symbols for precipitation, cloud cover, and wind direction/speed at reporting stations.


How Pilots Use Surface Analysis Charts

  • Identify pressure patterns to anticipate wind direction and strength.

  • Recognize frontal boundaries that could bring turbulence, icing, or thunderstorms.

  • Plan for alternate routes if widespread IFR conditions or hazardous weather is depicted.


The Surface Analysis Chart gives pilots a solid understanding of what is happening right now at the surface.


Low-Level Prognostic Charts

What They Are

The Low-Level Prognostic Chart (Prog Chart) is a forecast chart designed to give pilots an overview of expected weather conditions at the surface up to 24,000 feet (FL240). It is specifically tailored to aviation and is issued four times daily.


Types of Low-Level Prognostic Charts

There are two main types of low-level prog charts:

  1. 12-Hour and 24-Hour Forecast Charts

    • Provide a broad look at significant weather patterns.

    • Show pressure systems, fronts, and areas of predicted precipitation.

    • Include outlooks for ceiling and visibility restrictions.

  2. Low-Level Significant Weather Prog Chart

    • A specialized version focusing on weather hazards.

    • Identifies areas of IFR conditions, MVFR conditions, turbulence, and icing potential.

    • Highlights freezing levels, which are critical for avoiding icing hazards.


Key Features

  • Shaded Regions: Areas of expected IFR or MVFR conditions.

  • Lines of Turbulence: Marked with dashed lines to show regions of forecasted moderate or greater turbulence.

  • Freezing Levels: Shown as contour lines, helping pilots assess icing threats.

  • Fronts and Pressure Systems: Similar to the surface analysis chart but forecasted for the future.


How Pilots Use Low-Level Prognostic Charts

  • Plan fuel and altitude strategies by anticipating turbulence or icing along the route.

  • Adjust departure or arrival times to avoid forecasted IFR conditions.

  • Select alternate airports based on forecast visibility and ceiling conditions.

  • Gain a big-picture view of expected weather for strategic flight planning.


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Conclusion

Surface Analysis Charts and Low-Level Prognostic Charts are essential weather tools in aviation. The surface chart gives pilots a snapshot of current conditions, while the low-level prog chart provides a forecast of what lies ahead. Used together, these charts empower pilots to anticipate hazards such as icing, turbulence, and IFR weather, ensuring safer and more efficient flight operations.



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