Translation:They will play soccer if the weather is good.
Right now it only allows "if the weather is good".
"There is good weather" or "There is a good weather" both sound wrong to me.. It's like, the weather always is, the question is only whether it's good or bad. What do you think? (I'm not a native speaker so need a comment...)
There's no "will" in the if-clause in first conditional http://www.grammar.cl/english/first-conditional.htm