Which is why I said, the map is BS regarding today's climatic conditions, due to the fact the prevailing winds, would blow the ash from west to east, not east to west.
The maps are of ash that is actually deposited in geological formations, so the talk of wind direction is somewhat immaterial - if you notice, the ash spreads in a fan from the source, with some going out at right angles to either side of Yellowstone, an event that huge could make its own course in the form of pyroclastic flows.