After some early-day storms, there was another weather phenomenon Sunday that caught people's attention near Oshkosh.A funnel cloud was spotted over Lake Winnebago, but this wasn't your typical funnel cloud.It was what's known as a cold air funnel, and the weather on Sunday was a perfect setup for these cold air funnels.We had a strong low-pressure system and cold front pass through. That brought in cool air on blustery northerly winds. The large area of low pressure also provided plenty of what's called "vorticity" - this is essentially a measure of the spin in the atmosphere.With cool air aloft, air warming near the ground will start to rise. But as the air starts to rise, that column of air also starts to get stretch out vertically. And with all the vorticity in the atmosphere, that air starts to rotate, and as it stretches vertically more and more, rotates faster and faster, like a figure skater spinning faster by bringing their arms into their body.This process for forming a funnel is different from a normal funnel cloud; those require a large, rotating parent thunderstorms.Cold air funnels, in contrast, tend to be much weaker and rarely touch down, as was the case on Sunday.
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