On the morning of December 20, the stronger cold air from the north began to affect Shanghai, and the sky cleared. The cooling of this cold wave weather is not as large as the last time, but because the base temperature is already very low, December 20 is cold on cold, and the temperature is 1 throughout the day1~4.2℃。
Weather on December 21.
On the morning of December 21, the minimum temperature in the urban area dropped to -3 with freezing, and -6 to -4 in the suburbs with freezing or severe freezing. It's even below zero all day.
Specific forecast: sunny to cloudy, minus 3 to 0, northwest wind 5 gusts 6 7. Air humidity 70% 40%.
Tips: On December 21, the temperature was below freezing all day, so you must do enough to keep warm
Freezing or severe freezing in the morning, clean up the stagnant water in time, and pay attention to the vehicle to check the antifreeze;
The air becomes drier and the electricity load becomes larger, so pay attention to the safety of fire and electricity at home.
Weather trends. Friday entered the "winter solstice" in the 24 solar terms, and the prelude to the "counting nine cold days" was kicked off in trembling!It is expected that the minimum temperature at Xujiahui Station in the central city will be -3, and the suburb will be even lowerThe maximum during the day is only 2!
Although the daytime temperature has entered an upward channel since Saturday, it is still below freezing in the morning and evening. The warmer temperature will be more obvious in the middle of next week, and the maximum temperature will say goodbye to single digits. The next 10 days will be generally sunny and cold, and the work of cold protection and warmth is still the top priority.
Tips: The air gradually becomes dry later in the week, so everyone should pay attention to hydration. On the 22nd, it is the winter solstice to sweep, and everyone must pay attention to the safety of the festival.
Meteorological trivia:
According to the current forecast, Xujiahui Station will have a minimum temperature below -1 for 5 consecutive days (21 and 25 days). Statistics show that in the past 40 years, there has been no weather with a minimum temperature below -1 for five consecutive days at Xujiahui Station in late December. In a similar vein, there were four consecutive days in 1991, 1993 and 1999, and this time the continuous low temperature was really a long standby.
Air quality. 
At 17:00 on December 20, the real-time air quality index in Minhang District was 52, good, and the air quality was acceptable, but some pollutants may have a weak impact on the health of a very small number of abnormally sensitive people. A very small number of people with unusual sensitivities should reduce outdoor activities.
According to the forecast of the Shanghai Environmental Monitoring Center, the air quality in the morning, afternoon and night of December 21 was excellent and good, and on December 22.