Thursday, November 6, 2014

November 8-12 Potentially Significant Winter Storm

Model guidance is in agreement of a strong winter storm traversing the Central US. As a result, this storm's title has been upped to a 'Potentially Significant' storm.

The image above shows the most recent GFS model forecast for the next 120 hours' snowfall accumulation. In this map, we see the winter storm pounding parts of northern Iowa, southern Wisconsin and northern Illinois with over 6 inches of what would likely be some rather heavy snow, before dropping 4-6 inches in most of Michigan. The GFS model is taking the furthest south track out of major guidance, and we'll discuss that later on. The point is, however, the GFS is favoring a significant storm in the Midwest.

Tropical Tidbits
Next up, we have the GFS-Parallel model. This model is the new version of the GFS, which will be implemented in coming months. It has been rumored that this new model resolves biases in the current GFS model, with more accurate forecasts. This outlook has a swath of 12-18" of snow slamming central Wisconsin into southern Minnesota, with that heavy snow also hitting Michigan. Eyeballing it, maximum accumulation totals look to be on the order of 18-20". Clearly, this model favors a further north, even stronger storm track than the GFS. Let's see what other guidance has to say.

Tropical Tidbits
It just keeps getting worse, I suppose. This is the latest GEM model forecast of snowfall over the next five-ish days. The GEM model, from the Canadian Meteorological Centre (one of the other agencies that also spells the word as 'centre'), is notorious or exaggerating snowfall forecasts, and that is well seen in the image above. Here, we see a bullseye of around 24" of snow (two feet), pounding northern Iowa into Southern Minnesota. Wisconsin sees lesser, but still impressive amounts well above the 12" benchmark. Michigan also observes plowable snow.

We've gone through three model guidance forecasts, and have come to the idea that the GFS-Parallel and GEM support a northern track, while the GFS supports a southern track. Let's throw some ensembles into the mix and see what we can see.

This image shows the NCEP (GFS) ensemble forecast of extratropical cyclone tracks in the next handful of days, where each line shows a different track from a different ensemble member. Ignoring the mess in the East Coast, we look around Illinois and see several lines, all very spread out. These spread-out lines, indicating spread out tracks on the upcoming storm, tell us that high uncertainty still remains with this storm. Some ensemble members go south to downstate Illinois and mid-Missouri, while others stay north into southern Wisconsin. We can't really derive anything of significance from here, other than confirming that high uncertainty remains.

For my personal view of the storm, I feel there are two possibilities.

1) Model guidance has a good handle on what's going on right now. Heavy snow will hit central Wisconsin into Minnesota, with accumulations nearing 12", if not slightly more.

2) Model biases come into play, in this case the GEM and GFS-Parallel being too slow with advancing the Arctic air southward. This would push the storm southward as well, resulting in a track similar to the GFS.

For the time being, I'll side with the North Camp of models, just because the GFS seems to be on its own with the more southern track. I'll have more updates as we move closer to the storm.