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 spreading outward from thunderstorm downdrafts, appearing as a tan dashed line on surface analysis charts.
These low-level boundaries pose significant aviation hazards, including severe turbulence, strong wind gusts, and dangerous low-level convective wind shear, especially when they precede their parent thunderstorms.
Outflow boundaries are detectable by ground-based NEXRAD radar and sometimes visible satellite imagery, but are often filtered out of datalink weather broadcasts, requiring pilots to actively monitor METARs and local radar for detection.

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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.