>What supervolcano are you predicting? The last Yellowstone caldera distributed its tephra only within the range roughly of the Great Plains--people in Chicago wouldn't see ashfall.

Mt St Helens dropped from trace amounts to 1/2 inch of ash as far south as most of Colorado and as far east as western Minnesota. Ritzville, more than 250 miles away, had 2-5 inches of ashfall. Mt St Helens was comparable in volume to Vesuvius and was less than 1 cubic kilometer of volume, Oruanui eruption which was a relatively small super volcano eruption was estimated around 1170 cubic kilometers and dumped 7 inches of ash 620 miles away on the Chatham Islands.

Toba released between 2000 and 3000 cubic kilometers of ejecta (800 cubic kilometers being ashfall), killed a significant portion of humans alive at the time, created a genetic bottleneck responsible for the current genetic makeup of billions of people, lowered the temperature as much as 27F in places (5.4-9F globally). They found ash deposit from it in the South China Sea 600-800 miles away. If that happened in the middle of America, keep in mind the U.S. exports an absurd amount of its crops, you're talking bye bye population in North America, considerable cooling for Europe which would likely mean no crops in northern Europe. Then you lose the oil, natural gas and coal exports from North America. Air travel would likely be grounded for months the world around, if we keep assuming it's yellowstone in this scenario then if it happens in the winter here southern hemisphere crops would likely have poor yields depending what part of summer it is, if it happened in the summer here then European and Asian crops would suffer. Massive food shortages, fuel shortages, abnormally cool weather which could further effect crop growth and could get some areas into freezing temperatures during winter consistently instead of extremely rarely. Mt St Helens triggered air quality detectors in the northeastern United States so you'd likely have a deterioration in air quality the world around as well. Of course as most of the population of North America is dying from the ash fall starting in as little as a day or two you now have fewer and fewer people to fight fires when they break out, at some point you likely have massive fires burning through entire cities adding more smoke and ash to the atmosphere, some of these will move into forests unchecked, ash will have toppled some to many trees allowing fires to spread easier in forests, even if someone was here to launch planes to try and extinguish the planes the ash won't have cleared enough from the air to allow flight. Etc etc, so on and so forth. What the other guy in this thread, and the people downvoting me forget, is that the last time one of these happened... we were living in very very primitive structures and our population was likely under 1 million (at 10,000 BC population estimates are between 1 and 15 million, the last supervolcano eruption happened around 24,000 BC, lake Toba around 74,000 BC).

Toba was 100x more powerful than Tambora that I think I saw mentioned elsewhere in this comment chain. tambora happened in 1815 and cooled global temperatures by 0.95F / 0.53C, per wiki

>The second-coldest year in the Northern Hemisphere since around 1400 was 1816, and the 1810s are the coldest decade on record. That was the consequence of Tambora's 1815 eruption and possibly another VEI-7 eruption in late 1808. The surface temperature anomalies during the summer of 1816, 1817, and 1818 were −0.51 °C (−0.92 °F), −0.44 °C (−0.79 °F), and −0.29 °C (−0.52 °F), respectively.[8] Parts of Europe also experienced a stormier winter.

That wasn't even a supervolcano.