As the current storm heads out of Atlantic Canada, a lively but moisture-starved arctic front will move across the GL region through this evening. This will spark more LES as it deliver another punch of cold air in it’s wake.
Meanwhile a clipper disturbance will begin to track out of the Prairie Provinces and across ON/QC early this week. EC has weather statements up for parts of SK today and also for ON tomorrow into Tuesday with relation to this incoming clipper. General amounts of 5-10cm are forecast for S ON & QC, though some localized totals could be in the 12-15cm range before the action shifts to the east coast.
This impulse should redevelop near or along the coast later Tuesday through early Wednesday and affect Atlantic Canada as it intensifies. Guidance has been fluctuating with the eventual strength of the developing storm but there’s reasonable support for the central pressure to be in the 965-970mb range as it moves towards Labrador mid-to-late week. Coastal regions of NS and NL are expected to be on the milder, rainy eastern flank once again.
This is the latest sequence via this morning’s GFS.
Try to keep in mind that the snow total images represent the entire predicted snowfall over the period in question, sometimes encompassing multiple events and/or lake-effect and not accounting for compaction or possible surface melting. This is also an important factor in areas being affected by the ongoing storm in the east since some of it’s moisture will be included until it marches out of the picture.
06z GFS @ hour 36 / 48 / 60 / 72 / 84 / 96 (Monday afternoon through early Thursday AM):
Total snowfall (inch) @ hour 108:
The overnight Euro’s solution over the same span of time.
00z ECMWF total snowfall (10:1 inch) @ hour 108:
Snow probabilities for 10+cm on days 2 & 3 from the WPC:
A (temporary?) moderation in the pattern is anticipated farther out into the mid-range, although that doesn’t necessarily equate to a reduction in active weather with the western ridge degrading to some extent and more shortwave energy coming in.
Long-term hints for the remainder of December and a sizable portion of January will be available with the next run of the Euro weeklies tomorrow night.
Confessions of some snowlover's 
The coastal system’s involvement in S QC could really spruce up snowfall totals. 5-10 cm predictions here in Montreal are rapidly turning conservative as the driest solution, the GFS is turning wetter to the point that every reputable model is in the 15-25+ cm range. The 00Z NAM had some totals of 60 cm just to my north not counting any potential wraparound CCB banding on Wednesday afternoon, which will affect much of S QC.
As long as the WAA kicks in from the coastal unlocking the moisture at sea, the snow will fall very hard (possibly over 5 cm/hr). These heavy bands will be located for the most part north of Montreal but those aren’t forecasted to persist over many areas, and slow and steady could very well win the race as snow falls from early Tuesday morning to Wednesday evening in the St. Lawrence Valley.
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This is the latest regional Canadian in 12 hour increments from Monday AM through the evening hours and into Tuesday AM (which is the extent of it’s 48-hour range).
12z RDPS @ hour 24 / 36 / 48:
Plus one frame from the NAM which takes us to Tuesday evening as the coastal low gets underway.
12z 3km NAM @ hour 60:
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Montreal has received 0.7 to 0.9″ of QPF by 00Z Wednesday on the 3K NAM. Kuchera map has 25 to 30 cm by then. Wind gusts are in the 50-75 km/h across the valley so blowing snow seems like a good bet on Tuesday night and Wednesday as the isobars tighten near the deepening coastal low.
Ottawa receives just under 0.4″ of QPF.
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Snowfall graphics from this afternoon’s run of the Euro, covering the clipper as it pushes across the Prairies and then redevelops farther east.
12z ECMWF total snowfall @ hour 96:
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SWS have expanded to include a corridor through QC along the St Lawrence. Wouldn’t be surprised to see some of these regions move up to warning criteria in relation to the secondary development.
Here are the updated snow probabilities for 10+cm from the WPC – http://www.wpc.ncep.noaa.gov/index.php
Day 2:
Day 3:
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The Canadian short-range models have significant dry slotting for much of S QC after about 15-20 cm falls on Tuesday afternoon. They are known for puny solutions both snow and thunderstorm-wise at that start of their 48 hour ranges.
I think we’ll achieve snowfall warning criteria here.
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