Latest Forecasts Offer Few Answers About Weekend Storm

Posted at 11:18 AM, Dec 20, 2013
and last updated 2013-12-20 11:27:40-05

GRAND RAPIDS, Mich. — While a handful of details are becoming more clear about how a potent storm system will affect West Michigan this weekend, Friday morning’s new computer forecast information provided little clarity as to how much rain, snow, and ice specific locations in the area will see.

Every six hours or so, we receive a new onslaught of forecast information from the numerous computer models that simulate conditions into the future.  However, there are two significant issues with the information we continue to receive as of Friday morning:

  1. Different computers continue to disagree with each other, as well as with their own simulations with each successive time period; and
  2. West Michigan appears to be falling in an area of the storm’s trajectory that makes it especially sensitive to these minor fluctuations.

Let’s deal with the first issue.  There is somewhat better agreement as to the timing and track of the storm than in the last couple of days; still, differences of 50-100 miles are common.  This map shows the projected placement of the storm’s center as it moves into Lower Michigan Sunday morning, according to each of four different computers:

Model Comparison

Storm Track Model Comparison for Sunday morning 12/22/13

The average tends to delineate a storm track that runs from around Fort Wayne through the Detroit region.  However, that brings us to problem #2 — minor shifts around that line mean extremely different outcomes for West Michigan communities.

Take, for example, a snowfall forecast from a model taking a more southerly track (the exact numbers aren’t important to these examples, just note where the heaviest bands are indicated by dark blue and purple):

Model Comparison Snow 1

Model Comparison Snowfall Example 1

However, one of the more northerly tracks would create a scenario something like this:

Model Comparison Snowfall Example #2

Now, notice that this isn’t a big difference for people in most of Wisconsin, Detroit, or Indiana.  But for most of West Michigan, it means the difference between heavy snowfall and little to no snow at all.

Despite all of the difficulties, there are a couple of things in the forecast in which we’re starting to feel a bit more confident:

  • Snow totals of six inches or more will be most likely to the north and northwest of Grand Rapids.  Areas southward around I-94 will likely see much less snowfall — at most a couple of inches — through Sunday afternoon.  There will probably be a very sharp cutoff to heavy snow accumulation.
  • A band of significant freezing rain may affect locations just to the south of the main snow band.  As much as a half-inch of ice could accumulate (essentially double what fell on Friday), causing potential power outages in addition to travel problems.
  • The heaviest single band of rain will likely stay to our south and southeast, just trying to nose its way into the southern part of the state Saturday night.  Total precipitation will end up around an inch (give or take) from the storm system — the lingering questions mostly involve the proportion of rain/ice/snow that falls in any given location.

We hope that by Friday evening, we’ll be able to produce a pretty good draft of a snow accumulation map.  However, you can expect that if you live close to the edge of any particular band of rain, ice, or snow, you are liable to see significant changes in the forecast before the storm hits Saturday night and Sunday.

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