Breakdown: Outflow Boundaries: What they are & why so cool

Published: Aug. 17, 2020 at 10:24 AM CDT
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MEMPHIS, Tenn. (WMC) -Have you ever felt a cold rush of wind outside when thunderstorms are near? That cool breeze is probably due to an outflow boundary from a storm.

An outflow boundary, can also be referred to as a gust front forms when rain-cooled air from the downdraft of a thunderstorm hits the ground and spreads out ahead of a storm or in the direction that the lower level surface winds are flowing.

This outflow boundary will provide a sudden gust of cooler air that you feel before a storm arrives.

two outflow boundaries converge Wednesday afternoon in Tipton Co
two outflow boundaries converge Wednesday afternoon in Tipton Co

The outflow boundary can often times be detected on radar. As it moves along it can lift insects, dust, and debris along its leading edge. It shows up on radar as a thin line on the reflectivity setting of a Doppler radar. It can sometimes be even more clearly on the velocity or wind setting of a radar.

The boundary can also provide lift to warm, moist air in advance of it triggering a thin line of brief precipitation over an area as it moves through. Additional storms can sometimes develop along these boundaries especially if the atmosphere is unstable enough and there are abundant heat and moisture at the surface.

In many cases, the outflow boundary provides a brief cool breeze for those in its path.

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