Why is it so dry in winter in Beijing 20 17?

Since the beginning of winter, there has been rain and snow all over the country, but there has been no large-scale snowfall in Beijing for a long time, and it has been rated as the "driest city" in eastern China by netizens. Monitoring shows that the average relative humidity in Beijing has been less than 40% for more than half of the time since June 2065438+June 2007+June 2065438+10. 20 18, 65438+ 10, 1 1, and the relative humidity in Beijing is even lower than 20%.

65438+1October 2 1, the first large-scale snowfall in Beijing since winter. "The first snowfall in Beijing is165438+1October 29th, and the first snowfall in Beijing this year is 53 days later than normal." The chief forecaster of the Central Meteorological Observatory said. Although the snowfall was complained by city residents that there was no "white head overnight".

On record, the longest continuous days without effective precipitation in Beijing have reached 1 14 days (197010/25 October to197/kloc-0 February/kloc-0.

The lack of precipitation in Beijing occurred under the background that the precipitation in the whole country was generally less than in previous years. From June 5438 to February last year, the average precipitation in most parts of the country was less than 50%, and in many places it was even less than 80% on average. Two large-scale rains and snows at the beginning of 20 18 effectively alleviated this abnormal situation, and the rain and snow just "bypassed" the Beijing area.

According to the forecast of the Central Meteorological Observatory, there will be heavy snow in southeastern Henan, eastern and southern Hubei, most of Anhui, central and southern Jiangsu, Shanghai, northern Zhejiang, northwestern Jiangxi and northern Hunan from/kloc-0 to October 26, and there will be heavy snow in some areas. In addition, there are small to moderate rains in southern Sichuan Basin, western Guizhou and western South China.

According to experts, the formation of snowfall requires three conditions: precipitation system, sufficient water vapor and cold air. Song Wenling, chief forecaster of the National Climate Center, analyzed that since February 2065, 438+07, 65 and 438+07, the north wind in Beijing-Tianjin-Hebei region has been strong, that is, the cold air is strong, and the water vapor from the south is poor, which belongs to the "dry and cold type". The air is relatively dry and the conditions for snowfall are not sufficient.

"Aojiao" water vapor refused to go north, which is the main reason for the dryness of Beijing urban area. According to the national distribution map of precipitation anomaly percentage in February 2065438+2007 released by the National Climate Center, the average precipitation in most parts of Beijing in that month was less than 80%. Continuous dry and cold weather without rain and snow can easily lead to respiratory diseases and allergic diseases. Experts pointed out that precipitation in North China, Huanghuai and other places continues to be less, and the weather is dry, so the public should pay attention to hydration.