When I woke up yesterday, I felt a disturbance in the force. Something wasn't quite right, but I couldn't put my finger on it. I shrugged it off and got ready for the day. As I sat eating my breakfast and watching the boob tube, I was stunned by what I saw. I had turned to the Weather Channel. It was showing the radar for the upper midwest. The winds were spiralling clockwise, from the southeast. And it was raining.
Yes, I know what you're thinking. This is impossible right? I mean, every first year climatology grad student is taught that northern hemisphere cyclones spiral counter-clockwise. I mean, everybody knows that, right?
What I saw on the Weather Channel confused and disturbed me. I felt my entire climatological knowledge base slipping away. Everything I know was suddenly suspect. This was a life-changing event!
In retrospect, I realize now that there were certain factors at play that I wasn't aware of. The radar playback which I had seen yesterday morning had only shown the upper midwest, not the entire continent. Had I seen this, I would have realized the true driving force behind this seemingly impossible occurrence. As you can see in the satellite image above, there was a weak midlatitude cyclone centered over Illinois and Indiana. This was creating southeasterly winds over northern Illinois and Lake Michigan and on into southern Wisconsin. The northern part of this midlatitude cyclone was bringing rainy weather to Madison at the time. Meanwhile, a frontal boundary was advancing southward from Canada. This created a low pressure trough. In the proccess, the frontal boundary overpowered the weak pressure gradient of the dying midlatitude cyclone to the south. This caused those southeasterly winds over southern Wisconsin to take a right hand turn over central Wisconsin and head northward towards the frontal boundary. Thus, we have what appears to be a clockwise spin and rainy weather.
You can all rest easy. The world has not gone mad.
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