First, I'm not sure if you made that yourself, or what, but that's just a circle of X radius around Yellowstone - that might be useful if the Earth had no atmosphere, I guess?
Prevailing winds and jet stream guarantee a more distributed pattern downwind, significantly different than a simple circle.
BTW, the original article is missing pretty much anything of substance, and is written atrociously: "...In the Midwest, a few centimeters of ash is projected to be plummeted while coastal cities will have a few millimeter of ash buildup..."
"...to be plummeted..."?
AN ACTUAL MAP FROM ASH 3d:
http://cdn.phys.org/newman/gfx...
And an actual article that explains that whole "sciencey" stuff:
http://phys.org/news/2014-08-y...
Their slightly more substantive version of the above paragraph:
"...In the simulated modern-day eruption scenario, cities within 500 kilometers (311 miles) of Yellowstone like Billings, Montana, and Casper, Wyoming, would be covered by centimeters (inches) to more than a meter (more than three feet) of ash. Upper Midwestern cities, like Minneapolis, Minnesota, and Des Moines, Iowa, would receive centimeters (inches), and those on the East and Gulf coasts, like New York and Washington, D.C. would receive millimeters or less (fractions of an inch). California cities would receive millimeters to centimeters (less than an inch to less than two inches) of ash while Pacific Northwest cities like Portland, Oregon, and Seattle, Washington, would receive up to a few centimeters (more than an inch)...."