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Winter is well under way in North America with two distinct lake-effect snow events taking place since Thanksgiving. Lake-effect snow is common across the Great Lakes region, and happens when cold air originating from Canada passes over the relatively warm waters of the lakes, causing the layer of air near to the surface to absorb heat and moisture. Warmer than the air above it, this layer of air then starts to rise, cooling and condensing into clouds which deposit snow on the windward side of the lakes.
In this particular event, an area of low pressure centred across eastern Canada dragged very cold Arctic air in from the north and plunged it into the north-east of the US. The dry, arctic air blew in from the north-west across the relatively warmer Lake Erie through Thanksgiving, picked up moisture and deposited snow across areas to the south and east of the lake. A dominant band of snow brought rates of 2.5cm to 7.6cm (1in to 3in) an hour to the Erie and Crawford counties. Within the first 12 hours, approximately 30cm of snow fell in Ashtabula County, Ohio, and by Saturday morning, there were reports of more than 90cm of snow in the far north-east of Ohio and north-west of Pennsylvania. As a result of this heavy snowfall, parts of the Interstate 86 and 90 were shut on Friday 29 November.
There was a lull in snowfall over the weekend as the winds changed direction, but it wasn’t long before north-westerly winds returned with further snowfall. Another 30cm of snow was brought to parts of the previously affected regions. The highest amount of snow recorded from the two events was 162cm at Girard in Pennsylvania.
Further lake-effect snowfall is expected this week as a winter storm looks to track from the south across the north-east of US on Wednesday, bringing a very cold westerly, north-westerly flow across the Great Lakes through Thursday. Forecast models suggest a further 7.6cm to 20.3cm of snow could be possible across these previously affected regions as well as to the east of Lake Ontario. Meanwhile, just to the north-west of the Great Lakes, the arctic air will bring super-cold temperatures to the city of Winnipeg, Manitoba, with maximum temperatures -24C, which is 17C to 18C below normal for this time of year.
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In South Africa, citizens are undergoing their third heatwave of the season. The heatwave, which started last week, is anticipated to continue through this upcoming week with the hottest temperatures expected in the east. One of South Africa’s capital cities, Bloemfontein, can expect temperatures continuously exceed 35C each day this week and into this weekend. The hottest days look to be on Tuesday and Wednesday when temperatures may peak just in excess of 40C, almost 10C higher than the climate average on those days.
