Monday, 15 April 2013 | Weather
An occluding cyclone (a low-pressure cell that is filling-in and dissipating) is quite prominent over Minnesota on the IR/visual image of the upper Midwest Monday morning, April 15th. (This image is live, and will look different if you’re viewing at a different time). The northbound portion of the circulation has brought a temporary respite in Madison from the endless winter we’ve been experiencing. But, light snow is likely to be back in the forecast by Friday the 19th.
A listener called in last week to ask about an article she had seen in the Wisconsin State Journal about “atmospheric rivers.” This term was coined in the 1990s to describe the predominant mode of moisture transport away from the tropics toward the poles, which tends to occur in long, narrow plumes. A caller several months ago asked about the structural causes of these plumes and I still need to make good on answering him. The causal mechanisms are still under study, but what is known so far is quite interesting. I’ll talk about them on air soon since the local “AR” here in the upper MIdwest is the low-level jet which transports moisture from the Gulf of Mexico; it’s most active in the upcoming warmer seasons. In fact, some of the nearly 3 inches of rain that came down in Madison between April 7th and 14th was delivered by the LLJ.