Here's a map of the forecast tracks for low pressure systems across Canada this week. Obviously we're interested in the series of lines that indicate a low pressure system moving across our region. The lines all indicate that we'll have precipitation for some period of time on Wednesday: not a doubt. The question now is which track it takes: each coloured line shows a potential track (as predicted by various models): if the system tracks off the coast (i.e. the green line), then we would expect snowfall: being on the western side of the low, and the air would be coming from the northeast (counter-clockwise around the low pressure: classic nor'easter). If the system tracks to the west of Nova Scotia (i.e the blue line), then we might expect more in the way of rain or sleet (air flowing from the south and east, bringing warmer temperatures). You'll notice that the temperature range is wide for Wednesday (-10 to +4): this range is indicative of the uncertainty of the specific track. Some forecasters are starting to tend towards the offshore track which could mean heavy snow (see post below).

Fun stuff!