I. Convective activities ii. Surface wind greater than or equal 50kt iii. Hail at surface is 3⁄4 inch or greater in diameter iv. Tornado, v. Thunderstorm vi. Squall line cover at least 60 miles with thunderstom affecting at least 40 % of its length vii. An area of ts affecting at least 3000 square miles covering at least 40 %