Then, the NCEP ensemble mean 500 mb anomalies for 12/25 0z were:

The latest NCEP ensemble mean 500 mb anomalies for 12/26 0z are:

The 500 mb anomalies for 12/21/1974 were:

The 12/18-21/1974 period saw the following snowfall totals for select cities.
Chicago: 4.1"
Des Moines: 3.8"
Detroit: 6.4"
Indianapolis: 2.6"
Milwaukee: 7.5"
Windsor: 6.5" (16.5 cm)
At last word, the major features are somewhat farther to the south and east on the ensemble mean than they were on 12/12. Considering also the 12z ECMWF and GFS and the 18z GFS, I believe the highest potential for accumulating snow will involve an area across parts of Indiana, eastern Michigan, western Ohio, and parts of Ontario (including Windsor and London). In this area, I believe some locations could see several inches of snow (initially, 2"-4" seems reasonable with a few spots picking up a little more).
Eastern Ohio, western Pennsylvania, and southern Ontario, including snow-starved Toronto, should see at least a little snow as the storm heads away. There is a chance that Toronto could pick up several centimeters of snow.