Storm Update Dec 10-11

Current thoughts on this storm with regards to the first wave of low pressure. With a low developing in the SW U.S and tracking up into southern ontario I am anticipating a mostly rain event for southern ontario if you live south of georgian bay. Some mixing may be felt on the front side as some cold air presses southwards in contact with the over running precipitation. Models have been trending SE recently especially the GFS and ECMWF model guidance. This may be a signal that some more cold air will get involved causing a longer period of mixed precipitation or snow before a change over to rain and then possibly back end snow again. This is yet to be determined until tomorrows 12 and 18z runs which will have the sampling of the energy moving inland from the pacific ocean. In terms of eastern ontario there might be a different story with more surface cold air holding on as the low moves through. ECMWF and GFS model guidance have been indicating Warm air advection in advance of the LP system in the lower and mid levels of the atmosphere. While this is going on the surface temperatures stay at or below zero with over running precipitation which tells me that freezing rain and sleet can be a concern across eastern ontario, southern quebec and even central ontario. These areas are more prone to CAD and I think we will see this setup with the models under going a potential high east of the LP center. Models are likely over phasing a low that moves up to greenland before our storm moves into the area which closes the window for a significant surface high to build across eastern quebec. I see an initial shot of snow for ottawa and montreal before a changeover to a mix with sleet or freezing rain and then maybe a change over to rain later on. The GFS is more bullish on more frozen precipitation while the euro argues for a shorter period. These details will be ironed out on the weekend as modelling gets better sampled and i have a better idea on the exact track on the LP system. To sum up I see a potentially significant freezing rain/sleet and mixed precipitation event for eastern ontario and southern quebec in a line from parry sound to montreal. A swath of snow will set up in an area north of the Montreal and Ottawa. This swath will include quebec city where precipitation will stay mostly as snow with a 7-15cm+ swath and highest amounts across eastern quebec. Southern Ontario is the lowest confidence right now and model guidance still has to be sorted out with recent SE trends to get a better understanding on precipitation type. Right now i am going with a short period of snow and mixing out in front before a change over to rain and a potential change back to snow to end off the system. Updates to come this weekend and and map will come out on sunday. Feel free to ask any questions you may have that have not been covered in my post. 2m temp and precipitation maps are at or below zero in the corridor I mention which has the potential to see significant freezing rain and sleet. Notice 850mb temperatures are warmer then 0c which allows this to setup.

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