A huge storm system crossing the U.S. threatens to unleash tornadoes Friday in the Mississippi Valley, blizzards in the northern Plains and dry, gusty conditions in Texas and Oklahoma that pose an extreme risk of wildfires.

A sweeping storm system moving across the U.S. threatens to bring tornadoes, blizzards and possibly wildfires to different regions of the country

The holiday is observed on March 14 or 3/14 because 3.14 are the first three digits of the infinite number pi — 3.14159 ... and on and on. The celebration of Pi Day was the brainchild of physicist Larry Shaw and was first observed in 1988 at San Francisco’s Exploratorium,

From schoolkids learning about constant numbers to pizza deals to school serious math equations, here’s a slice of Pi Day fun.