The National Weather Service has issued a severe thunderstorm watch for portions of Arkansas, Oklahoma, and Texas. The advisory is in force until 12 p.m. Saturday. The watch includes big cities, including Dallas, Sherman, and Texarkana. The storm system has the potential to produce hail up to two inches in diameter, wind gusts of 60 mph, and frequent lightning. The National Weather Service predicts that scattered storms will affect more than nine million people, including 2,715 schools and 175 hospitals.