Weather is the ultimate ice-breaker. Anyone who has been in an awkwardly long elevator ride, or in a taxi Lisbon, knows what I'm writing about. However, there's an art to this whole "weather ice-breaking method". A good conversationalist will tell you that commenting on the weather alone, or complaining about it, it's not really a weather conversation - that's just chit chat. If you want to use weather to break the ice, and eventually lead to a more meaningful talk, there are three very successful approaches to it:
a) the environmental approach: first you comment on the weather, stating whether it's cold, warm, rainy, etc. And then just go about telling how it used to be "in the old days", and that maybe all that talk on the icecaps melting away in the poles, and ice ages, makes sense. If you are comfortable on this theme, you should quote sources, this may lead to a talk on media today, how books are expensive, and so forth. If by any chance you quote Al Gore, than you are safe. From Al Gore you can go to American politics, elections, politics in your own country, TED Talks and a myriad of other different and totally unrelated themes.
b) the housewife approach: if the person you're talking to is also a housewife, you'll be on safe land imediately. Just comment on how the weather is helping/hindering your household tasks: laundry, changing winter clothes to summer clothes, how the gas/electricity bill is higher this time of the year. Once you mention your electricity bill, you're opening the door to a wider range of subjects: inflation, natural resources (environmental approach is on the brink here), and politics once again. A poor conversationalist will stick to exchanging housework tips, this is convenient if you are in the lift, the rides are usually short.
c) the medical approach: comment on how the weather is affecting your good health: "ah this heat makes my legs swell". If you're Portuguese, you'll have a LOT to talk about, besides you have to make a point on how the weather is worse for you than for other people, and this alone should keep you quite busy. If not, just bring about in the conversation the last time you went to the doctor, and you'll find that the person who you're talking to has his/her own rant against the national health system or insurance companies. The medical approach will leave you busy for several hours. This approach is recommended on chemists', post offices' or hospital's queues.
It seems that even in blogs, that are written monologues, weather can give you a hand to get started. :-)