What Is an Outflow Boundary Shown on a Surface Analysis Chart?

Here's a step-by-step guide to deciphering surface analysis charts—particularly ‘gust fronts.’

Wednesday, May 01, 2024 at 12:01 PM ET

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During the spring, summer, and fall, it is common to see the surface analysis chart issued by meteorologists at the WPC include dashed lines labeled as an outflow boundary. [Courtesy: National Oceanic and Atmospheric Administration.]

Key Takeaways:

An outflow boundary, or gust front, is a mesoscale cold front formed by cold, dense air from thunderstorm downdrafts spreading outward, appearing as a tan dashed line on surface analysis charts.
These boundaries pose aviation hazards such as severe turbulence and low-level wind shear due to abrupt shifts between strong updrafts and downdrafts, especially if they move in advance of the parent thunderstorms.
Pilots should utilize NEXRAD Doppler radar (for low reflectivity lines), visible satellite imagery (for cumuliform clouds), and surface observations (METARs for gusty winds) to detect outflow boundaries, as they are often filtered out of datalink weather broadcasts and require strict avoidance when hazardous.

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Question: What is an outflow boundary shown on a surface analysis chart?

Answer: When looking at the surface analysis chart issued every three hours by meteorologists at the Weather Prediction Center (WPC), you may have seen a tan dashed line with a label “OUTFLOW BNDRY” nearby. This is what meteorologists call a convective outflow boundary.

You may view North American surface analysis here.