continental interiors related to blocks experience severe winters, a phenomenon which has been known since the discovery of the North Atlantic Oscillation in the 1840s. These blocking patterns also have a tendency to produce anomalously mild conditions at very high latitudes, at least in those regions exposed to anomalous flow from the ocean as in Greenland and Beringia, or from chinook winds as in Interior Alaska. Such cold winters over the contiguous United States and southern Canada as 1911/12, 1935/36, 1949/50, 1977/78 and 1978/79, 1993/94, and 2017/18 resulted from blocks in the Gulf of Alaska or to the east of the Mackenzie Mountains directing very cold Arctic air with a long trajectory as far as the American South, as did the Western cold waves of 1889/90 and January 1950. In Northern and Western Europe, cold winters such as 1683/84, 1739/40, 1794/95, 1829/30, 1894/95, 1916/17, 1941/42, February 1947 and 1962/63 are almost always associated with high latitude Atlantic blocking and an equatorward shift of the polar jet stream to Portugal and even Morocco. Over Central Asia, unusually cold winters like 1899/1900, 1929/30 and 1930/31, 1944/45, 1954/55 and 1968/69 are associated with blocking near the Ural Mountains extending the Siberian High westwards to push the very cold air from the Siberian “cold pole” outward towards the Aral and Caspian Seas. Unlike other midlatitude regions of the Northern Hemisphere, however, cold winters in Europe (e.g. 1916/17, 1962/63) are often very mild over Central Asia, which can gain warm air advection from subtropical cyclones pushed to the south under negative NAO conditions. Heat waves Heat waves in summer are the result of similar blocking patterns, typically involving the placement of the semi-permanent subtropical ridge. Some unusually intense summers such as 1936 in the United States, 1999, 2002, and 2011, and in Europe summers such as 1976, 2003 European heat wave, and 2019, were the result of entrenched highs that became detached from the jet stream for a prolonged period of time and allowed warm, dry air to build in place. In many cases such as the 1999 US drought, the heat wave was preceded by prior months of below normal precipitation that prevented temperatures from cooling. The 2003 heat wave in Europe occurred, conversely, during a year that North America experienced markedly below normal temperatures and higher than normal precipitation, especially during the spring months. The high amount of rain in North America increased