Tuesday, November 29, 2011

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December 4-9 Major Snow Event (Updated 11/29)

12z ECMWF Snowfall

12z NOGAPS Ensembles with outlined areas. Lines inside the outlined portion indicate a possible track.

12z NCEP Ensembles. Tracks inside the black lines are possible ensemble tracks.

12z GFS (red) and 12z GEM (pink)
The Midwest remains in the potential line of fire for a major winter storm heading into the December 4-9 timeframe. The first image details the ECMWF's solution. The ECMWF continues to keep north, not budging at this time. Snowfall accumulations would easily rise above 6 inches in this scenario that the ECMWF is showing.
The second image is made up of the 12z NOGAPS model ensembles. At this time, pay attention to the models that are inside the black lines. Those are the models that are tracking this storm. The NOGAPS ensembles are keeping on the southern track at this time, which is somewhat surprising considering the NOGAPS itself is on a more northerly track at this time. However, because the models are not too good at this time, we are more angled to trust the ensembles.
The third image details the NCEP ensembles. Again, pay attention to the tracks inside the black lines. The NCEP ensembles are following the GFS, but at this time appear to be a tad more southerly than the actual GFS. We are again more apt to go to the ensembles at this time of model mayhem.
The fourth image is comprised of the 12 GFS and 12z GEM models. The GEM/GFS appear to be on a similar track until Illinois, when the GEM dips south as the GFS continues a northeast track.
All that said, here's the current camps of north track and south track.
The north track is above North Illinois, while the south track is below North Illinois.
(ENS. stands for ensembles)

North Camp: NOGAPS, ECMWF, DGEX, JMA, ECMWF Ensembles
South Camp: GFS, NOGAPS Ensembles, NCEP Ensembles, GFS Ensembles, GEM, GEM Ensembles

Ratio of North Camp to South Camp is 5:6 out of 11 models in favor of the South Track.

It does look like a ridge in the east and a cold outbreak in the North Plains will be two key factors in this storm track. The ECMWF pushes the warmer air farther westward, thus bringing the storm track in the same direction. The 12z GFS is more forceful with the cold air and keeps the storm track down south. However, the GFS has started to trend north, as illustrated in the below picture:
Past 4 cycles of GFS (see color key on bottom right)
The GFS, as you can see, has been very stable the last couple runs but has trended north for one run. We are waiting for the 0z run to see if this change will continue or if this run was a fluke.

We are thinking that a blend of the ECMWF/GFS is a good idea at this point, but definitely leaning with the ensembles as the models struggle in some spots.

If you want to see the models for yourselves, check out our updated Weather Models Page, now housing 144 links for 25 models.