By Mark Torregrossa

This winter's severity is starting to add up for a few Michigan cities. An index has been developed that ranks the severity of winter.

The severity of winter compared to what locals are used to is highest in southeast Lower Michigan. The severity lessens as we look north in Michigan.

(MLive file photo)

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How the index works

The Accumulated Winter Season Severity Index (AWSSI) was developed by the National Weather Service to rank each winter against previous winters and average winters. The AWSSI uses daily temperature, daily amount of snow and snow on the ground to quantify the severity of a winter.

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Detroit having the most extreme winter of Michigan cities

The winter severity index at Detroit is currently ranking Detroit's winter as extreme. The black line shows the current value. The different colored areas give you a feel for the various stages of winter severity. So far this winter, Detroit's Accumulated Winter Season Severity Index shows Detroit is having the most extreme winter of the ranked Michigan cities.

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Lansing inching toward extreme winter

Lansing's AWSSI is just under the extreme status. A few days of harsh weather this week would push Lansing into an extreme winter. That category may not hold, as much milder weather is on tap for late week.

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Grand Rapids on the verge of extreme winter

The Accumulated Winter Season Severity Index for Grand Rapids shows the first part of winter has spent many days in the severe category. Right now Grand Rapids is running on the edge of a severe and extreme winter.

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Alpena having an average winter

Looking at Alpena's winter so far emphasizes a strength in the AWSSI. The AWSSI adjusts for long term average weather as you move north. Alpena and Detroit could have the same value for the AWSSI, with Alpena being ranked average severity and Detroit ranked more severe. So far Alpena is having an average winter.

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Marquette just into the severe ranking

Marquette's winter is pacing just above average, into the severe ranking.

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How's the rest of the U.S. pacing

This map shows how the various ranked cities are pacing for this winter. Purple dots represent extreme winter conditions. Extreme winter is being experienced from southeast Michigan into the Northeast and Mid-Atlantic. The southwest U.S. is having mild to record mild conditions so far this winter.

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What a difference a year makes

Last winter ended as a mild winter for most of the eastern two-thirds of the U.S. The seven cities ranked in Michigan had either a moderate or mild winter last winter. Extremely severe winter weather was confined to the northwest U.S.

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