The daydreaming is over. A strong factor in many travellers' plans is how to avoid winter weather, summer heat, and monsoons. Reported temperatures may be just the average for the day. You will rarely hear two people predict the monsoon season the same for any area, and you cannot assume that the weather is the same just because two places are near each other. One person's idea of 'comfortable' weather can be unbearable for another.
Many travel books have charts and information, but there are also books specifically for weather.
Don't try to fine-tune your exact schedule for the optimal weather in each place. Northern Manchuria extends as far north as parts of Southest Alaska. Beijing is at the latitude of Philadelphia, Hong Kong as far south as Havana. East China gets enough rain year-round for paddy rice. Much of central China is semi-arid steppe.