Anatomy of a Storm: Midwestern Blizzard February 2007

Current weather bulletin for my corner of the world from from the U.S. National Weather Service:

“A blizzard warning is in effect tonight for all of South Central and Southeast Wisconsin. Snowfall tonight will reach 8 to 14 inches (20 to 36 cm) with some locally heavier amounts possible across much of the area. Strong easterly winds gusting up to 40 mph (64 km/h) at times will result in blizzard conditions at times with visibilities severely restricted to one-quarter mile (400 m) or less at time tonight into Sunday…..The heavy snow may be accompanied by lightning and thunder.”

Sure enough, about half an hour ago as I was doing the research for this article I could hear the rumble of thunder along with the howl of old man winter. As the above weather bulletin reads, the Upper Midwest especially Wisconsin is being slammed with a blizzard.

Here’s the current weather map for the Upper Midwest from the Weather Channel’s website.

As I’m writing this, there is very powerful low pressure system (the red “L” is the center) that is packed full of moisture. The light purple front line is called an occluded front and represents the merging of cold and warm fronts found in strong systems. (This will be explained in future artices). The faint white lines represent the same atmospheric pressure along the line. As you can see the lines are packed together tightly over the upper midwest. This means lots of wind because air is rapidly moving to stabilize the pressure gradient.

The driving force behind all the moisture and wind is the jet stream that is currently very dynamic. Below is the path of the current jet stream:

The very sharp upward swing of the jet stream helped to steer the system rapidly from the moisture-rich southern US and rammed the storm into the cold winter air of Wisconsin.

More importantly, the current jet stream is very fast-moving and created a stronger cyclonic effect on this low pressure area. This is known of extratropical cyclogenesis. Another way to describe this is that the jet stream helped to form a tighter ball of low pressure energy. Although the process of formations are vastly different, this is the same cyclonic effect that makes hurricanes so powerful. The low pressure center is essentially the “eye” of this storm.

There you have it. I’m just glad that I don’t have to go out tomorrow.

Update: The next two articles will be a north to south tour of this nasty storm system. The article about the freezing rain in Illinois can be found here and stay tuned for a 3rd article on the tornadoes to the south.

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Posted by Tim Roth, author of the political blog Think Anew and Act Anew

Sources:
1. National Weather Service Bulletin from the Milwaukee, WI office – February 24, 2007 (no permalinks available)
2. Weather Channel TV broadcast February 24, 2007
3. Weather Channel website – Current Midwest Weather and Jet Stream (no permalinks for these constantly changing maps)
4. “Blizzard”, Wikipedia entry
5. “Cyclogenesis”, Wikipedia entry