the weakened immunity and malnutrition leading up to the Black Death (1348–1350). 1600–1602, extremely cold winters in Switzerland and Baltic region after eruption of Huaynaputina in Peru in 1600. 1607–1608, in North America, ice persisted on Lake Superior until June. Londoners held their first frost fair on the frozen-over River Thames. 1622, in Turkey, the Golden Horn and southern section of Bosphorus froze over. 1690s, extremely cold, snowy, severe winters. Ice surrounded Iceland for miles in every direction. 1779–1780, Scotland's coldest winter on record, and ice surrounded Iceland in every direction (like in the 1690s). In the United States, a record five-week cold spell bottomed out at at Hartford, Connecticut, and in New York City. Hudson River and New York's harbor froze over. 1783–1786, the Thames partially froze, and snow remained on the ground for months. In February 1784, the North Carolina was frozen in Chesapeake Bay. 1794–1795, severe winter, with the coldest January in the UK and lowest temperature ever recorded in London: on 25 January. The cold began on Christmas Eve and lasted until late March, with a few temporary warm-ups. The Severn and Thames froze, and frost fairs started up again. The French army tried to invade the Netherlands over its frozen rivers, while the Dutch fleet was stuck in its harbor. The winter had easterlies (from Siberia) as its dominant feature. 1813–1814, severe cold, last freeze-over of Thames, and last frost fair. (Removal of old London Bridge and changes to river's banks made freeze-overs less likely.) 1883–1888, colder temperatures worldwide, including an unbroken string of abnormally cold and brutal winters in the Upper Midwest, related to the explosion of Krakatoa in August 1883. There was snow recorded in the UK as early as October and as late as July during this time period. 1976–1977, one of the coldest winters in the US in decades. 1985, Arctic outbreak in US resulting from shift in polar vortex, with many cold temperature records broken. 2002–2003 was an unusually cold winter in the Northern and Eastern US. 2010–2011, persistent bitter cold in the entire eastern half of the US from December onward, with few or no mid-winter warm-ups, and with cool conditions continuing into spring. La Niña and negative Arctic oscillation were strong factors. Heavy and persistent precipitation contributed to almost constant snow cover in the Northeastern US which finally receded in early May. 2011 was one of the coldest