I think it would be helpful to also compare to the northern half of the Caspian sea.
City: latitude (coldest average high/coldest average low)
Caspian Sea
Baku: 40°23′43″N (43.3F [6.3C]/35.6F [2.0C])
Derbent: 42°03′N (39.7F [4.3C ]/ 31.6F [-0.2C])
Makhachkala: 42°58′N (39.6F [4.2C]/29.3F [-1.5C])
Aktau: 43°39′N (34F [1C]/28F [-2C])
Astrakhan: 46°21′N (31.8F [-0.1C]/19.2F [-7.1C])
Atyrau: 47°07′0″N (27F [-2.8C]/14.2F [-9.9C])
Great Lakes
Cleveland: 41°28′56″N (34.4F [1.3C]/21.7F [-5.7])
Chicago: 41°50′13″N (31.5F [-0.3C]/18.2F [-7.7C])
Erie:"42°7′46.42″N (33.7F [0.9C]/20.8F [-6.2C])
Milwaukee: 43°03′8″N (28.9F [-1.7C]/15.6F [-9.1C])
Petoskey: 45°22′24″N (28F [-2C]/13F [-11])
Coper Harbor: 47°28′08″N (23.1F [-4.9C]/9.8F [-12.3C])
The Caspian sea area is colder than the black sea area, but still warmer than the great lakes, of course the Caspian is much larger and extends further south, however the northern portion does freeze over in the winter, and the water is basically fresh up there too because of the huge inflow from the Volga.
http://www.parstimes.com/MODIS/CaspianSeaDec2002.jpg
And this is the Black sea in the winter
http://www.universetoday.com/wp-cont...mo_2015008.jpg