The forecast for Sydney to Singapore tomorrow courtesy of a Qantas Facebook chat:
Dave Egan: Very broadly out of Sydney tomorrow will be an excellent day. On route there is currenlty a jet stream expected to be about the NSW/QLD border at about 10am. There could be some mild turb here. Then usually as you approach SIN you would expect thunderstorm activity in the afternoon. Which is very common for their area, but it has been quiet this week so you may get lucky.