What the weather condition can affect for flight? What is the most disturbing weather conditions for flight? 
On another word: what more dangerous for takeoff/landing: wind, precipitation or something else?
It's actually fairly simple when talking about weather related dispatch delays for the airlines.  

Number one items:

In summer, thunderstorms, especially those associated with fronts and squall lines.

In winter, snowstorms with heavy accumulations, or severe freezing rain.

And beyond that, in both summer and winter, extreme low visibility, as in fog.