Seems more and more likely that the storm coming this weekend on the 17th -18th will feature rain at some point, with the possibility of some back end snow.   Watch for Environment Canada and TWN to start updating their outlooks with warmer temperatures and some rain in the forecast.  Their is potential that areas in the Ottawa valley around the city of Ottawa either stay as wet snow, or switch over to freezing rain overnight on Saturday Dec.18th.  Not enough details to make a call either way at this point, but keep this in mind if you have travel plans.  Right now it looks like a possible 8 – 15cm snow events across southern and eastern Ontario, with rain and mixing in most locations eventually.
Here is the possible snow totals in inches from the storm:gfs_asnow_neus_20
First though, we head into the coldest air of the season starting tomorrow into Friday.  Low’s on Thursday night will be in the -20’s range.  We then warm up Saturday with the storm and cold behind it on Sunday Monday before we warm up again mid next week for Christmas.
Midweek Christmas update
The potential storms on the models from Dec.22 – 27th also have a rain feature as a strong possibility, depending on whether they actually develop where they end up.  Keep in mind from my Sunday post that they will want to track west with the Southeast Ridge flexing its muscles.
Therefore I am quite sure that areas around the GTA and south and west in Southern Ontario will likely be a green Christmas, or right on the borderline (maybe 2 cm on the ground).
I suspect that areas around Barrie and the LES regions of Georgian Bay towards central Ontario into Ottawa will have enough of a snowpack to maintain some snowcover, at lease up until Dec.24th.
It will really depend on how many hours of rain we experience on Dec.17-18th and whether the system develops during the Dec.24 -25th time period that cuts enough west for rain.  I think my map from Sunday is still a good call at this point.