In the winter, however, the vast Siberian High causes very cold, north to northwesterly winds that bring temperatures as low as −5 °C (23 °F) in the extreme south and −30 °C (−22 °F) in the north[38] where the zone of discontinuous permafrost reaches northern Heilongjiang. However, because the winds from Siberia are exceedingly dry, snow falls only on a few days every winter, and it is never heavy. This explains why corresponding latitudes of North America were fully glaciated during glacial periods of the Quaternary while Manchuria, though even colder, always remained too dry to form glaciers[39] – a state of affairs enhanced by stronger westerly winds from the surface of the ice sheet in Europe.