Group 1 - The core point of the article is the arrival of a significant cold air mass in China, marking the first large-scale cold air event of the second half of the year, which is expected to bring noticeable temperature drops across various regions [1] - The cold air will primarily affect northern China over the next few days, leading to record low temperatures for the year in cities such as Xi'an, Yinchuan, and Zhengzhou, with daytime highs potentially dropping below 20°C for the first time this season [1] - In northern regions like Heilongjiang and Inner Mongolia, temperatures may fall to single digits, with some areas even approaching freezing, indicating a significant shift towards autumn [1] Group 2 - The cold air mass will also push the summer monsoon southward, allowing northern China to transition fully into autumn by the end of the week [4] - In southern China, while the cold air will not lead to an immediate autumn transition, it will help alleviate prolonged high temperatures, with cities like Hangzhou expected to see highs drop below 30°C [6] - Despite the incoming cold air, southern regions are still experiencing extreme heat, with Nanchang setting a record for the most high-temperature days this year, indicating that heat management remains crucial for residents [6]

Group 1 - The northern regions of China have been experiencing record-breaking heavy rainfall since July 23, with some areas receiving nearly a year's worth of rain in a single day [1] - A total of 19 weather stations in northern China have broken historical monthly precipitation records, with 13 stations setting all-time highs [1] - The extreme rainfall has resulted in cumulative precipitation exceeding 100 millimeters in several areas, with some regions like Shijiazhuang and Baoding surpassing 400 millimeters [1] Group 2 - The Central Meteorological Observatory has issued a yellow rainstorm warning, predicting heavy rain to continue but with a weakening trend over the next three days [2] - Areas expected to be affected include parts of Inner Mongolia, Shaanxi, Shanxi, Hebei, Beijing, and several other provinces, with localized heavy rain and strong convective weather possible [2] - Despite the expected reduction in rainfall intensity, caution is advised, especially during nighttime when heavy rain is more likely [2] Group 3 - The causes of the heavy rainfall in North China are complex, involving sufficient moisture from the summer monsoon and the influence of cold air from the westerly wind belt [3] - The topography of the Taihang Mountains enhances the efficiency of moisture condensation, contributing to extreme localized rainfall [3] - The phenomenon known as "three typhoons dancing together" is related to the rainfall but does not have a direct causal relationship with the current heavy precipitation events [3]