How big would the explosion be and the aftermath if the Yellowstone volcanoes all go kaboom?

This article from wikipedia describes past eruptions and current conditions including this:

“The last full-scale eruption of the Yellowstone Supervolcano, the Lava Creek eruption which happened nearly 640,000 years ago[13], ejected approximately 240 cubic miles (1000 cubic kilometres) of rock and dust into the sky.[8]

Geologists are closely monitoring the rise and fall of the Yellowstone Plateau, which averages ±0.6 inches (about ±1.5 cm) yearly, as an indication of changes in magma chamber pressure.[14][15]

The upward movement of the Yellowstone caldera floor—almost 3 inches (7 centimeters) each year for the past three years—is more than three times greater than ever observed since such measurements began in 1923.[16] From mid-Summer 2004 through mid-Summer 2008, the land surface within the caldera has moved upwards, as much as 8 inches at the White Lake GPS station.[17] The U.S. Geological Survey, University of Utah and National Park Service scientists with the Yellowstone Volcano Observatory maintain that they “see no evidence that another such cataclysmic eruption will occur at Yellowstone in the foreseeable future. Recurrence intervals of these events are neither regular nor predictable.”

The trouble of supervolcanoes is not a single big explosion, but the accumulation of ejecta over a period of time. Usually several vents will open up.

Volcano winter would be somewhat likely. It seems to have happened before with those volcanos.