Dandan looks at the weather丨Today ushered in the coldest day in the second half of the year, the suburbs fell to -2°C. Why does the cold air always “check in” on weekendsFly into the homes of ordinary people
Xinmin Evening News (Reporter Ma Dan) The cold wave is raging, and the temperature in Shanghai has reached a new low, ushering in the coldest day in the second half of the year. This morning, the minimum temperature in Xujiahui in the urban area fell to around 1℃, and it was even lower in the suburbs. The extreme minimum temperature was as low as -2℃~2℃. Although there is sunshine during the day, the sunshine is like the light in the refrigerator compartment, which has limited help in heating up. According to the forecast from the Shanghai Central Meteorological Observatory, this cold wave came quietly and went fast, and the temperature will gradually rise from tomorrow. It will continue to be fine and fine weather from the 19th to the 22nd, and the temperature will rise day by day. The minimum temperature is expected to gradually rise to 7°C, the highest. The temperature will rise to 16~17℃ again. Wu Rui, chief service officer of the Municipal Meteorological Bureau, said that this cold wave is going a bit anxiously, especially when the highest temperature will reach 17℃ next Tuesday, which will make Shanghai’s successful entry into a weather-significant winter with twists and turns.
Since November, Shanghai has experienced 4 cold wave weather processes, and the temperature has dropped significantly, but the temperature has also been particularly rapid. As a result, Xujiahui Station in the urban area has been unable to meet the winter entry standard (the entry standard for Shanghai meteorological significance: daily average temperature for 5 consecutive days) Below 10℃, the first day is the winter day). Compared with the annual average (1981-2010) winter start time of December 3, the winter start time of this year at Xujiahui Station, which has climatic statistical significance, is indeed late. However, from the city level, many suburban areas have entered the meteorological winter on December 1.
The recent cold air seems to prefer weekends. Generally, it always arrives in Shanghai before the weekend, and then cools down from the weekend to the beginning of the week, and then the temperature warms up. The familiar formula makes people curious. Is this really a coincidence? “It’s not always true.” Meteorological experts explained that the high-altitude wind around the middle and high latitudes of the earth winds from west to east, presenting large-scale fluctuations, which can bring warm tropical air to the north and cold air from the Arctic to the south. , And the middle and high latitudes of the northern hemisphere are greatly affected by the fluctuation of this circulation. On forecasters’ weather maps, there are usually two technical terms “groove” and “ridge”-the most protruding part of the isobar is called a high-pressure ridge, and the most concave part is called a low-pressure trough. Generally speaking, the place controlled by the high-pressure ridge is mainly downflow. The weather is clear and the temperature rises. There are more updrafts in front of the low-pressure trough. With water vapor, there is frequent rain and snow. . This trough and ridge, which is thousands of kilometers long, is a long atmospheric wave. Its cycle is about 3 to 5 days. Therefore, the cold air activity in winter also has a certain regularity. “The cycle and intensity of the cold air will be affected by the strength of the ridges. If a certain cold air coincides with the weekend, it may hit a new stream of cold air next weekend. This is the main reason why cold air loves to get stuck. “Wu Rui said.
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