29 May 1998 -- Convection Along Intersecting Outflow Boundaries

GOES-8 visible

GOES-8 visible image - 18:59 UTC

(Java animation)

The atmosphere was moist and unstable over Alabama, Georgia, and much of the southeastern U.S. on 29 May 1998. As daytime heating further destabilized the atmosphere, isolated pulse-type thunderstorms formed over west central Georgia after around 17:00 UTC. Outflow boundaries from these short-lived storms were evident on NOAA GOES-8 rapid scan operations (RSO) visible imagery (above). New convection can be seen forming along the intersection of these earlier outflow boundaries, and this new convection was more organized and long-lived than the preceeding storms.

GOES-8 sounder total precipitable water (PW) from 11:46 UTC that morning shows the abundant moisture across that region -- values of 40-50 mm were widespread, and the Atlanta/Peachtree City GA rawinsonde profile indicated 39 mm of precipitable water. By 17:46 UTC, GOES-8 sounder-derived precipitable water and lifted index (LI) showed the moist (greater than 45 mm PW) and unstable (LI less than -8 C) nature of the afternoon atmosphere.

Wind speeds at the surface and within the middle troposphere were very light (generally 10-15 knots or less) across the region at 18:00 UTC. This led to slow movement of the convective cells, and nearly circular outflow boundaries within the weak flow regime.

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