The ECMWF/s Stealth Miller B

Does today/s 12z ECMWF D+5 forecast a deepening Great Lakes upper LOW capturing and intensifying the M-A surface LOW toward the 'benchmark' @ 40°N / 70°W...

...or does it excite a 'back-door' Miller B and drag it onshore?

The upper LOW is shown coming in the back-door from ern CN instead of its more common direct approach from the NW. The upper LOW would be expected to develop a surface reflection on the E side of the short-wave trof. Given the deep...unstable vertical temperature and moisture profile...cyclogenesis would be rapid and intense.

Note the orthogonal (90°) crossing angle of the MSLP isobars (equivalent to the geostrophic wind @ the boundary layer/s top) and 5H Z to the E of the LOW indicating veering vertical shear and strong UVM from WAA. These dynamics will build the downstream short-wave ridge enhanced by the release of latent heat and slow the easterly progression of the upper air features.

The low resolution of the model post-processing may prevent the depiction of this feature.

Should the 'back-door' scenario come to pass...the snows over the M-A would pale in comparison.