If there are some key words to describe the climate or weather of Beijing, I think that would be ‘Dry’,’Wind’, ‘Dust’, and I know someone would argue the smog is one of these, but I don’t think smog is a natural thing or a climate, it is just the reaction or revenge from God.
Extremely dry, except for in the hot summer which humidity could reach to an awful 70-90%, is the typical feeling for people who lived in Beijing for years. The humidity of all other season is pretty low, which is probably below 30%. You may already be aware that, this is absolutely the enemy for the beauty, keeping hydrated of skin or a beautiful face is important for ladies. No women would like to loss skin elasticity.
On the other hand, the humidity in summer could be pretty high, reaching 70-90% sometimes, which bring some health problem for people who may have respiratory problem. it is usually coupled with a lower air pressure.
Humidity is relatively good in Fall and Spring, but during these two season, the wind become stronger, either the hot wind from southern or the cold wind from northern， which make the temperature gap between days to be more than 10C degrees (50F). People get cold easily during this time.
Also, wind may have a great possibility to bring tons of dust from Mongolia, which make the sky turning to dark red. And some of the dust can directly inhale into your nose. Have a mask is good when it comes. To be remembered, even you live in a good or upscale apartment, you can keep away from the dust, it would take only 1 day, you can see a layer of dust covered on your table. I am not exaggerating here.
Full of dust would also do harm to your electronic device, such as the speaker of iPhone, the hold for speaker would soon be blocked by the dust, and the output sound should be affected.
Summer and winter in Beijing is pretty long than the other two seasons, summer would started from May to Oct. And when July to Sep comes, the temperature would reach to 39C(102F), and average to 35C (95F). Winter is actually not as cold as in northern east China. The coldest day in beijing would just be -10C(14F), and usually would not last for more than 1 month. I think Jan and Feb would be that coldest day. To my personally feeling, the average temperature in Beijing would be around 0C(32F), and you will feel more colder if it is coupled with wind.
Like I just said, Fall and Spring have a dramatically temperature gap, the temperature would be from 5C(41F)-25C(77F), but it would not last too long, usually 1-2 month, then, summer or winder come.
One of the annoying thing for people who live in Beijing is the catkin from poplar tree in every spring (earlier Apr.) You see them everywhere, it is hell for the patient having rhinitis and asthma. And this would last for at least one month. If you have allergic to that, going to beijing on Apr. would not be a good choice.
Somebody should be responsible for this ‘disaster’, just because they think the poplar tree would grow faster than other trees when make plan for city development.
At last, the rain and snow are in general rare in Beijing, but sometimes, in summer, it would be storm. which would paralyse all the traffic, even killing people. And snow would do the same to the traffic as well.