You heard about the lake effect aspect of this upcoming system, now here is some information about the system aspect of this system.

A model consensus has formed with regards to a low pressure centre rolling through the Prairies then spawning a secondary low in the northern Plains on Friday or so. This low is currently expected to barrel through the Great Lakes on Saturday as shown in this WPC chart:9mhwbgloop

It indicates that S ON will have a wet prelude to the LES but farther north in E ON and S QC, the occlusion of the low is expected to protect us from the brunt of the warmth aloft, resulting in wet snow according to the 18Z GFS:GFSNE_prec_ptype_141

Unfortunately, other global models are warmer with either sizeable front-end snow (12Z GGEM) or no snow for YOW and YUL (12Z ECMWF). Environment Canada currently favours the ECMWF solution:

Colorado low arriving over the upper Great Lakes on Saturday..
Preferred Guidance: ECMWF (GDPS is too progressive)
Scenario Confidence Level: low to medium
The European models have a similar upper trough solution at T+144hrs while the
GDPS upper trough appears too progressive. So a weaker and slower surface
pattern like the ECMWF on days 6 and 7 is preferred. There is fairly good
continuity for the ECMWF surface and upper low positions on days 6 and 7. Heavy
snow and blowing snow to the north of the track of the low with significant
rainfall and strong winds are expected over the southern side with a band of
freezing band ahead of the associated warm front. 

The 12Z GFS is also incredibly progressive with regards to the H5 trough (15-18 hr difference). The disparity in timing grew further with today’s 18Z run, to about 24 hours.

The 12Z ensemble means for the GGEM, ECMWF and GFS tend to replicate the respective deterministic solutions. I favour the ECMWF given the progressive bias that typically plagues the GFS around 144-168 hours out.

A tertiary low is also expected to form on Saturday, but its positioning will greatly affect any potential for heavy snow from it; the ECMWF places it considerably to the west of the GFS (in western New York), also predating the system’s occlusion, in a pool of warmth, only becoming dominant Some older GGEM solutions developed this low farther SE near NYC, quickly attaining dominance over the secondary and producing heavy snow in S QC.

With the growing divergence in solutions, something has to give eventually; H5 energy sampling is expected to commence at 00Z Wednesday and take full effect on 00Z Thursday, so a 60 hour lead time.

Please stay tuned for further updates.