The last contact with the flight was at 1721 UTC on Friday, March 7th (around 9:21 AM PST), somewhere between Malaysia and Vietnam (see map, courtesy of flightradar24.com)
Here is a map of the surface temperatures, surface winds, and satellite-based cloud cover at 1700 UTC on that day for the area in question. Satellite imagery shows nothing...no thunderstorms, clouds are anything else on the route. Surface winds are weak.
And here is an infrared image from the Japanese GMS satellite an hour before the aircraft was lost (1631 UTC). Absolutely NOTHING going on along the flight path...essentially clear skies.