Weather Summary - The first working day after the Spring Festival holiday in Shanghai will experience overcast weather with occasional rain, and local areas may accumulate moderate to heavy rainfall [1] - On February 23, the weather in Shanghai started sunny in the morning but became increasingly cloudy in the afternoon, with temperatures dropping significantly due to cold air, reaching a maximum of 15.4℃ at the Xujiahui station [3] - From the night of February 23, Shanghai will transition to overcast with occasional rain, continuing into the daytime of February 24, with local rainfall potentially reaching moderate to heavy levels [5] - Throughout the week, Shanghai is expected to have more rainy days than sunny ones, with significant rainfall expected on Thursday and Sunday, and temperatures remaining relatively stable between 12-15℃ for highs and 7-11℃ for lows [7]

Group 1 - The core point of the article discusses the weather conditions in Shanghai, highlighting the occurrence of fog with visibility less than 500 meters due to radiation cooling and moist air from the southeast wind [1][3] - On January 16, the fog gradually dissipated by noon, with daytime temperatures reaching around 19 to 20 degrees Celsius, specifically noting a high of 19.7 degrees Celsius at the Xujiahui station [1] - The weather forecast indicates a significant temperature drop next week due to strong cold air, with expected temperatures between 3 to 5 degrees Celsius and potential light rain or snow on January 17 and 18 [3]

Group 1 - Shanghai's temperature is experiencing a slight rise today, with the lowest temperature recorded at 5.3℃ in the city, while some districts dropped below freezing [1] - A cold air mass is expected to bring temperatures back down below 10℃ tomorrow, with highs only reaching between 2℃ and 7℃, and lows in suburban areas dropping to between -4℃ and -2℃ [1] - Next week, after a cold start on Monday with temperatures around 1℃, a significant warming trend is forecasted, with temperatures rising to 16℃-17℃ by midweek [4] Group 2 - The upcoming warm spell is described as a "retaliatory warming" during the coldest period of winter, which is somewhat unusual but has been observed in the context of global warming [6] - Historical data indicates that extreme temperature records in January have previously exceeded 20℃ in Shanghai, suggesting that such warm spells can precede subsequent cold fronts [6] - The weather will remain dry, with relative humidity dropping to as low as 20%, indicating a need for hydration and caution regarding fire and electrical safety at home [6]