I have taken a very close look at the 06 Z GFS run, and have returned to a conclusion pretty much the same as last time. I am thinking that the system will start with a prolonged period of freezing rain (due to the above-zero temperature in the Level 2 layer, or the 850 mB temp., and the sub-zero temperature near the ground, a perfect scenario to set up freezing rain). 

For much of the GTA, Precipitation will start at around 1 to 2 PM on Christmas Day, with freezing rain lasting for three or so hours before switching over to rain. The rain will fall at a rate around 0.3 to 0.5 mm/hr (generally light in nature), before switching back over to brief periods of snow on the backside of the Texas Low. The backside of the low is a concern for the latter part of Boxing Day and the following Sunday. I am expecting about 5 cm to fall on Boxing Day night and Sunday. Lake effect becomes more of a concern for the latter part of Sunday, and early parts of next week for the "traditional snow belt" region. Next week can also be bitterly cold, as foretold by the 850 mB temp, and the 1000-500 mB thickness. It looks like by next Monday night, the 850 mB temp can reach as low as -20 C for much of Southern Ontario, along with a thickness value close to 510. More about this will be posted after Christmas Day.

I cannot just trust my insight, and therefore, the raw data for 06 Z GFS was ran through the simulator yet again to produce an "adjustment" to my insight.

Here's the output of the simulator:

This afternoon: Dense overcast. High -3. Wind east around 12 kph.                                                                                                         

Tonight: Dense overcast. Low -5, but temperatures rising after midnight. Wind chill down to -11. Wind east around 16 kph in the evening, becoming 21 kph after midnight.

Friday: Dense overcast. A chance of a mix of rain and sleet in the afternoon. High 2. Wind east around 25 kph. Precipitation (liquid equivalent) mostly around 2 mm. No ice (on ground) accumulation expected.   

                                                                                                                                                 

Friday night: Dense overcast. A chance of a mix of sleet, snow, and rain in the evening, then a chance of a mix of snow and sleet after midnight. Low -2. Wind chill down to -8. Wind east around 22 kph in the evening, becoming west after midnight. Precipitation (liquid equivalent) mostly between 2 and 5 mm. No snow or ice (on ground) accumulation expected.   

Saturday: Dense overcast. Snow likely, mixed in with rain early. High 1. Wind west around 19 kph. Precipitation (liquid equivalent) mostly between 2 and 5 mm. Little (if any) snow accumulation expected. 

Saturday night: Dense overcast in the evening, becoming cloudy after midnight. Patchy light fog after midnight. A chance of snow in the evening, then a slight chance of snow after midnight. Low -5. Wind chill down to -8. Wind west around 13 kph. Precipitation (liquid equivalent) mostly less than 2 mm. Snow accumulation about a cm.                                                                                                                      

Sunday: Cloudy. Patchy light fog in the morning. A chance of snow. High -2. Wind west around 11 kph. Precipitation (liquid equivalent) mostly less than 2 mm. Snow accumulation less than one cm.   

Sunday night: Cloudy in the evening, becoming mostly cloudy to cloudy after midnight. Low -7. Wind chill down to -14. Wind west-northwest around 16 kph in the evening, becoming 21 kph after midnight.   

Monday: Mostly cloudy to cloudy. A slight chance of snow in the afternoon. High -6. Wind northwest around 27 kph. Precipitation (liquid equivalent) mostly less than 2 mm. Little or no snow accumulation expected.  

Monday night: Mostly cloudy to cloudy. A chance of snow. Low -10. Wind chill down to -16. Wind northwest around 21 kph in the evening, becoming 16 kph after midnight. Precipitation (liquid equivalent)  mostly around 2 mm. Snow accumulation about 2 cm.   

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Summary: Generally, for much of the GTA, this will be mainly a rain / mixed precip. event. Combined with my insight and the simulator output, I am expecting around 10 mm of rain and 2 - 4 cm of snow (from Friday to Monday). This will be a very active weekend, in terms of weather, which might cause a messy drive for holiday travel or holiday shopping. 

I will issue a city-by-city forecast later today. So stay tuned to my blog! Please also subscribe to my blog. Thanks.

Merry Christmas to all.