Emirates flight path for DXB to SFO
 

Looking at flightaware map,
http://flightaware.com/live/flight/U...425Z/OMDB/KSFO

For DXB to SFO, most days they are flying west. But some days (Mar 12, Mar 17) they flew east even though proposed flight path (dotted line) shows west.

Anyone know why? Just curious.

Almost certainly high-altitude winds on the day. A 100-mph jet stream working for or against you can make way more difference than a few great circle miles.

San Francisco and Dubai are almost exactly on the opposite side of the world. They are 177 degrees apart. The shortest route is almost straight over the north pole. My daughter snapped a selfie on the flight with the inflight map showing Santa's address.

Teh "east" and "west variations here are minor, exacerbated by trying to disply and the type of map projection flightaware uses. If you look at the actual paths on a globe, with something like the Great Circle Mapper page uses, I suspect you'd see they're pretty close to each other.

Keep in mind that at the top of this type of map, "half way across the world", half the width of the map, can be a few miles, or even a few feet, apart as you approach the poles.

Looking at the data, "west" is typically 173-175 degrees and "east" is 184-186.