winter solstice and thermal midwinter (coldest time) is not the same as between the summer solstice and thermal midsummer (hottest time). In much of East Asia with oceanic influences, including Korea and virtually all of Japan, January is the coldest month, but August is the warmest month. In low and mid latitudes, the summer lag is longer, while in polar areas the winter lag is longer (coreless winter in interior Antarctica and Greenland). In mid-latitude continental climates, it is approximately 20–25 days in winter and 25–35 days in summer. San Francisco, for example, has an exceptionally long seasonal lag in the summer, with average daily temperatures peaking in September, and October as its second-warmest month, but very little seasonal lag in the winter, with the lowest temperatures in December and January, around and soon after the winter solstice. This is caused by the water in the Bay Area surrounding the city on three sides. Many areas along North America's west coast have very small winter lag and are characterized by a much more gradual spring warming and relatively more rapid autumn cooling. Due to seasonal lag, in the Northern Hemisphere the autumnal equinox (around September 22) is considerably warmer than the vernal equinox (around March 20) in most regions despite the fact that both days have almost equal amounts of daylight and darkness. However even with seasonal lag the autumnal equinox is cooler than the summer solstice (around June 21) in most regions as well as the vernal equinox being warmer than the winter solstice (around Dec. 21) even in most oceanic areas. Contrary to popular belief, there is no meteorological reason for designating these dates as the first days of their respective seasons. In eastern Canada the seasonal lag is consistent both in summer and winter, resulting in February and August being the coldest and warmest months, respectively. In Western Europe the lag is lower in spite of the Atlantic coastline, usually around a month, which is also consistent with many inland areas in the North American Midwest. In Japan, Korea and nearby areas (for example, Vladivostok, Russia), seasonal lag is stronger in summer than winter; the coldest month is January, while the warmest month is August, possibly due to enhanced cloud cover and rain during June into July (for example, the "tsuyu" rainy season in Japan or the "jangma" season in Korea over the same period). On other