ところが
Usage
ところが is a sentence-initial conjunction used when something takes place which is unexpected from the preceding context. The sentence after ところが represents an event or action the speaker cannot control, as shown in the following examples.
Examples
先生のオッフィスアワーに研究室に行った。ところが、先生はいらしゃっらなかった。
I went to the laboratory during the Teachers office hour. However the teacher was not there.
天気予報は、今日は雨だと言っていた。ところが、とてもいい天気になった。
The weather forecast said today it will rain. However it was really good weather.