The Jury is out!

A significant Colorado Low will move into Southern Ontario Tuesday night... Heavy snowfall is expected for most of Southern Ontario with the exception of Niagara Pennisola and extreme Southwestern Ontario. Areas near Windsor should start seeing snow early in the evening progressing into London by Midnight, The GTA should start seeing snow Overnight.
Most areas in Eastern Ontario, Central Ontario as well as Southern Quebec should stay mostly snow throughout the direction of the event. While the changeover vary place by place around the GTA into Southwestern Ontario. Areas transitioned to rain will experience a brief period of backside snow slowly turning into Lake effect. WNW wind is expected to bring significant Lake effect snow behind this low.
Strong damaging winds are expected to bring at times blizzard like condtions to many areas. Here is the forecast for the selected regions:

Toronto 10-15cm start at 4 am transition to rain at 11am
Kingston 17-22cm start at 8 am brief period of rain late afternoon
London 8-13cm start at 1 am transtion to rain at 8am
St.Thomas 5-8cm start at 1 am transtion to rain at 5am
Barrie 18-23cm start at 5am brief period of rain early afternoon
Newmarket 13-18cm start at 4am transition to rain at 12am
Windsor 2-5cm brief period of heavy snow late evening to midnight
Hamilton 5-10cm start at 3 am transtion to rain at 8am
Niagara falls 2-4cm brief period of heavy snow to start off
Allison 16-21cm start at 4am transiton to rain at noon
Peterborough 18-22cm brief period of rain afternoon
Ottawa 23-28cm mixng possible
Montreal 22-27cm mixing possible
Quebec City 25-30cm


Here it is, my full forecast on this thing. Mind you, I will probably do an intermediate update sometime tomorrow. I've spend way too much energy tracking the model runs on this storm and I would not born you with every detail.

Method
With short range forecasting, I generally start to look down into the detail on things. Especially with this storm, where I think the rain/snow line would be a key factor, difference areas in Southern Ontario could get quite a different amount for the snow figure.

In order to get this forecast in good shape, I started to get away from the main models and start to look at radars, current data as well as the short range higher resolution models. This allowed me to give the best estimation on where exactly the rain snow line is going to be all the way across.

The rain snow line
With this storm, a 50 km difference could be alot. The rain snow line is rather relanctant to go over from the Niagara peninsula into the GTA eastward, meaning that anywhere Southwest of Hamilton could see substantially less than the areas northwest.



South???
Why is my forecast quite a bit south than the other forecast and what it appeared on the models recently? It was quite a pleasant surprise to see the models shifting quite a bit south this close in time range. This meant that the models may have underestimated the cold air above us. I fully expect this trend to stay especially with the short range models supportive of this fact.