While many are still suggesting heavy precipitation for this system for Southern Ontario, I, on the other hand, am thinking that Southern Ontario will see mostly light precipitation. Currently, it looks as if the low, when it heads up to the Great Lakes region, most of the energy will be transferred to the coastal region (New England / Canadian Maritimes), leaving very little for the Great Lakes. This is, of course, will lead to the development of another major weather story for the Canadian Maritimes, just in time for the end of 2009 to arrive.

According to the 12Z GFS model run, things are looking very grim for a White Christmas this year. This reminds me of last year, when Southern Ontario is suggested to receive 40 cm of snow about 2 weeks before Christmas. All of this did not happen, and we ended up having mixed precipitation for Christmas, if I had not remembered it wrong.

The model run is expecting significant warm air from the Gulf of Mexico to the Great Lakes well before any precipitation begins. It looks like the 540 line is pushed well north of most of Southern Ontario before the precipitation begins. Therefore, when precipitation do actual begin ahead parts of the system, around the morning hours of Christmas Day, the precipitation will begin as mixed precipitation. As temperature continue to rise on Christmas Day, the precipitation will switch over to periods of light drizzle and rain. It will not be until into the overnight hours before the precipitation switch back over to periods of light flurries and snow for the rest of Boxing Day, as the cold front pushes through the Great Lakes region. 

I know, it's disappointing that with so much cold air in place over Southern Ontario right now, this would turn out to be a rain event.

This system, for Southern Ontario, as far as I can see it, will mostly be a rain / mixed precipitation event. 

I have put this data and my own insight into the weather simulator, and the outcome results the following (the forecast is only valid for the Greater Toronto Area, you might use it for a reference for the rest of Southern Ontario):

This afternoon: Mostly cloudy. A slight chance of snow. High -3. Wind northwest around 10 kph. Chance of precipitation less than 20 percent. Precipitation (liquid equivalent) mostly less than 2 mm. No snow accumulation expected.    

Tonight: Partly cloudy. Patchy light fog after midnight. Low -13. Wind chill down to -18. Wind northwest around 11 kph.                                                                                                                            

Tuesday: Partly to mostly sunny in the morning, becoming mostly sunny in the afternoon. Patchy light fog in the morning. High -7. Wind northwest around 15 kph.                                                                                                                                                                      

Tuesday night: Mostly clear in the evening, becoming clear after midnight. Patchy light fog after midnight. Low -16. Wind chill down to -22. Wind northwest around 12 kph.                                                                                                                                                            

Wednesday: Sunny. Moderate fog in the morning. High -8. Wind north around 13 kph.                        

Wednesday night: Clear in the evening, becoming fair after midnight. Patchy light fog after midnight. Low -16. Wind chill down to -22. Wind north around 11 kph.                                                                                                                                                                      

Thursday: Partly cloudy in the morning, becoming mostly cloudy in the afternoon.  Patchy light fog in the morning. High -4. Wind east around 14 kph.                                                                                                       

Thursday night: Cloudy in the evening, becoming dense overcast after midnight. Low -6, but temperatures rising after midnight. Wind chill down to -11. Wind southeast around 18 kph.                                                                                                                                                 

Friday: Dense overcast. A slight chance of a mix of rain, snow, and sleet in the morning, then a chance of a mix of rain and snow in the afternoon, followed by drizzles late in the afternoon. High 3. Wind  southeast around 20 kph. Chance of precipitation 50 percent. Precipitation (liquid equivalent) mostly around 2 mm. No snow or ice (on ground) accumulation  expected.                                                                                                                                                                 

Friday night: Dense overcast. A chance of a mix of snow and rain in the evening, then a chance of snow after midnight. Low -4. Wind chill down to -9. Wind northwest around 22 kph. Chance of precipitation 50 percent. Precipitation  (liquid equivalent) mostly between 2 and 5 mm. No snow accumulation expected.   

Saturday: Dense overcast. A chance of snow. High -4, but temperatures falling in the afternoon. Wind northwest around 26 kph. Chance of precipitation 50 percent. Precipitation (liquid equivalent) mostly around 2 mm. Snow accumulation 1 to 2 cm.                                                                                                                                                                       

Saturday night: Dense overcast. A chance of snow. Low -11. Wind chill down to -20. Wind northwest around 28 kph. Chance of precipitation 50 percent.  Precipitation (liquid equivalent) mostly around 2 mm. Snow accumulation about 2 cm.                                                                                                                                                                       

Sunday: Dense overcast in the morning, becoming cloudy in the afternoon. A slight chance of snow. High -8. Wind southwest around 31 kph. Chance of precipitation less than 20 percent. Precipitation (liquid equivalent) mostly less than 2 mm. No snow accumulation expected.                                                                                                                            

Sunday night: Cloudy. Low -9. Wind chill down to -17. Wind southwest around 30 kph.      

Summary: I think the simulator over-emphasized on the cold air's impact after the system. I highly doubt it will be that cold on Boxing Day (Saturday), with a high of around 0. The chance of precipitation is just what the simulator suggests, as I have no control over that. 

Overall, the system will "dump" (if that's even the right word to use) 3 to 5 cm of snow, about 7 to 10 mm of rain. 

One thing that did not show up in the above forecast is the projected snow cover before and after Christmas. It looks like we WILL have a white Christmas, as 2 cm of snow will continue stick to the ground on Christmas Day, despite the rain / mixed precipitation. Expect around 7 cm of snow on the ground by the end of Boxing Day. 

Sunday might be an interesting day for snowsqualls developments. I'll keep you posted. Please subscribe to the blog. Thanks!

** My next forecast will be based on the 18 Z or 00 Z GFS, which will be released in about 10 hours. Stay tuned!