We are planning on spending the weekend in the country as long as weather stays fine.

• A. 
  We are spending the weekend in the country because of the fine weather.
• B. 
  If the weather is fine, we'll spend our weekend in the country.
• C. 
  If the weather was fine, we would spend our weekend in the country.
• D. 
  We won't spend the weekend in the country unless the weather is fine.