What caused the winds shift to the north?

a big bow echo was moving towards the east at 50 mph. The winds were out of the east at the surface because i was ahead of a warm front. As the storms moved closer i noticed the low clouds moving in from the northeast then the north as also the surface winds shifted to the north. then the gust front arrived and the winds shifted to the west. what was the north wind from? could it be a pre meso low