Winter Storm Wrap-up For February 7th, 2013

A major Winter Storm hit the Great Lakes region on Thursday, February 7, 2013 resulting in heavy snow across mainly east central and south central Wisconsin.   The storm system that brought the snow came out of the southern plains Thursday morning, then intensified as it moved northeast toward Lake Erie:

Warm air initially surged north ahead of the low bringing a wintry mix of freezing rain, sleet and snow to much of the area during the early morning hours.  By mid morning on Thursday, temperatures cooled rapidly, causing the mix to change over to snow quite rapidly (see below how Dual Pol radar technology helped us see this transition occur.)  In the end, 6 to 9 inches of a heavy, wet snow fell in an area roughly east of a Manitowoc, to Fond du Lac, to Beaver Dam, to Lake Mills, to Delavan line.  The highest totals were across southern Milwaukee, Racine and Kenosha counties. Snowfall amounts tapered off to the north and west of that area.  See the series of images below for plotted and analysed snowfall reports from our Cooperative Observer network. 

A regional perspective of the snowfall:

Here is how our  Dual Pol radar technology depicted the rapid change over to snow across parts of southeast and south central Wisconsin Thursday morning. In the loop, the first image is about 9:09 AM, the second, 10:15 AM and the final is during the afternoon when the precipitation was all snow.  This is an image called Correlation Coefficient (CC).  It shows us where there is large and small diversity among precipitation targets that the radar is sensing.  A mixed precipitation area would have a large diversity of target sizes, thus a CC less than zero.  Note how the area north of the yellow line becomes more uniform, closer to zero, in about a 1 hour span between about 9 and 10 am this morning.  This is when the transition to snow, low diversity targets (all targets about the same size), occurred.  Finally, the last image is what CC looks like once the entire area transitions over to one uniform type of precipitation...in this case snow.

 dual pol correlation coefficient

Davis



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