Tuesday, November 4, 2014

November 8-12 Potential Winter Storm

Model guidance appears to be toying with the idea of a winter storm in the November 8th-12th timeframe.

Tropical Tidbits
The image above shows the ECMWF model's forecast of mean sea level pressure (MSLP) contours and 850mb temperature values, valid for November 11th of next week. In this image, we see a strong storm system pushing north into western Illinois, dragging down sub-freezing air behind it only a few thousand feet off the ground. This 995 millibar storm would bring predominantly snow to areas north of the thin red freezing line, which would include Wisconsin and Iowa, among other regions.

I cannot post graphics due to copyright concerns, but this ECMWF run spits out over 12" of snow in parts of Wisconsin due to this storm. The ECMWF has shown this storm inconsistently for a few runs now, keeping uncertainty high.

Tropical Tidbits
The image above shows the GFS-Parallel model's forecast of MSLP values and 500 millibar geopotential height values, valid on November 10th. In this image, we see a messy set-up for this storm, with one low pressure system located in northwest Missouri, apparently attached to a very weak low pressure system in Michigan. This set-up would likely keep most snow out of the picture, save for the Upper Midwest, and is a plausible solution, given that this model will succeed the GFS model in due time.

This whole potential for a winter storm arises from what we saw happen in Japan a few days back.

The above image shows observed 500 millibar geopotential height anomalies over the Northern Hemisphere (left panel), as well as cloud cover and high/low pressure demarcations (right panel). Note how we saw a very strong storm stirring up near Japan on this date, which was November 2nd. We saw a strong trough wrap up and occlude just north of Japan, still bringing through a respectable shot of cold air. I had discussed earlier about how this could provide the basis for a potential winter storm, and it appears that this potential is being realized now.

Because this storm appears to occlude north of Japan, but still scrape the western side of the nation as it does so, I'm still content believing the risk for a winter storm remains. Just how great that risk is must be examined further, but the chance remains.

To summarize:

- Model guidance is indicating the potential for a winter storm to hit the Central US in the next week or so.
- Very high uncertainty exists with this storm potential.
- Depending on cold air availability, as well as if the storm actually happens, accumulating snowfall may be a concern.


1 comment:

Anonymous said...

What about the nao, it seems to be flattening out to the positive, maybe?