Wednesday storm: The science behind the spin-up


GRAND RAPIDS, Mich. (WOOD) — Severe storms rolled through West Michigan Wednesday night, with one producing potentially several tornado touchdowns spanning from eastern Kent County to far northern Eaton County.

The storm that likely produced a tornado began as a storm rushing in from the west across Ottawa County. Wind and rotation from storms is best viewed on “velocity” mode, which shows what the winds are doing inside each cell.

This storm was likely generating some wind damage as it raced due east. This is evident by the green bullseye moving into Ottawa County just after 7 p.m.

At the same time, a storm north of Grand Rapids was dumping so much cold rain that it began to generate a blast of wind tracking from the storm’s front to the south. This is called an outflow boundary. We can see that outflow boundary on velocity, too. It shows up as a thin line moving away from a storm.

As the storm moving in from the west approaching Kent County ran into the boundary rolling in from north to south, it created a collision, which starts spin in the atmosphere and can quickly trigger enough rotation to produce a tornado.

As these two components, as well a surge of warmth from the southeast, interacted Wednesday night, it likely did just that. Within moments, a notch had formed on the incoming storm zooming into Grand Rapids, spinning up a quick and tight circulation.

Strongest rotation was just on the northeast side of Grand Rapids and north of Ada.

>>Inside Photos of storm damage

After a likely tornado tore through northeastern Grand Rapids and Ada, the parent storm and the boundary racing south continued to bump into each other. This likely created pulses of tight rotation. The two elements continued to bounce into each other for miles, stretching all the way down to northern Eaton County.

Situations like this usually create a scenario where a strong parent storm can occasionally spin down several brief tornadoes. When the rotation tightens up, a tornado touches down, then lifts again as the rotation weakens.

This is why we likely have pockets of tornado damage from Grand Rapids all the way down to Sunfield.

Damage survey crews will be out to officially survey the damage and discern the path of the potential tornado after daylight Thursday.



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