Sunday, November 23, 2014

November 24th Potential Accumulating Snow

This is a regional discussion for accumulating snow potential in the Great Lakes. Please note these types of regional discussions will become more prominent this winter.

Model guidance supports a swath of potentially plowable snowfall in the Great Lakes on November 24th, into the 25th.

Instant Weather Maps
The image above shows total snowfall from this morning (Sunday) to Tuesday morning. In this forecast, from the NAM model, we can define a swath of 3-6" of snow from Iowa to Michigan in the light blue to dark blue colors, with amounts over 6" (and even approaching the 10" mark) depicted in the pink colors.

This snowfall potential comes from a storm system currently placed in the southern Plains, forecasted to move north in the next day or so. As this happens, it is expected that a band of precipitation on the backside of this storm will form, laying down accumulating snow in parts of the country. The question is, where could this occur? Right now, the NAM model shows the brunt of the snowfall hitting the Wisconsin/Illinois border, but as of its most recent 18z run, snowfall has been shunted to eastern Wisconsin and Michigan. Let's see what the GFS model says.

Instant Weather Maps
The GFS model supports a swath of snowfall hitting primarily Northern Illinois, as well as southern Wisconsin and eastern Minnesota. Amounts would be maximized near Chicago, where the legend tells us 4-5" would be predicted to fall. Lesser totals nearing 4" would then be forecasted in the Northwoods region. We are awaiting word from the 18z GFS model run as I type this to see if we can build any bit of consistency. Why do we need consistency? If you haven't noticed yet, we currently have three completely different solutions:

• Solution 1 (12z NAM in top image): Snowfall strikes the Lower Great Lakes. Rockford, IL into south-central Wisconsin sees the heaviest totals (over 6").

• Solution 2 (18z NAM, not shown): Snowfall fails to fall anywhere, save for Michigan and eastern Wisconsin. Amounts totaling 3-5" in most places.

• Solution 3 (12z GFS, image above): Snowfall impacts North Illinois primarily, laying down just under half a foot of snow.

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