January 31 – February 2, 2011 North American blizzard fell as freezing rain in the Philadelphia suburbs, a mixture of sleet and freezing rain in Berks County and the Lehigh Valley and mainly a snow and sleet mixture in the Poconos. Overnight colder air moved in aloft in over the Poconos and precipitation changed back to all snow for a few hours. Toward sunrise on the 2nd, this process started to reverse at both the surface and aloft. Warmer air was moving north again and the freezing rain changed to plain rain across the Philadelphia suburbs and Berks County around 8 a.m. EST and the Lehigh Valley around 9
Hail with air, wind, and interaction with rain and other hailstones can slow their descent through Earth's atmosphere. Severe weather warnings are issued for hail when the stones reach a damaging size, as it can cause serious damage to human-made structures and, most commonly, farmers' crops. Any thunderstorm which produces hail that reaches the ground is known as a hailstorm. Hail has a diameter of or more. Hailstones can grow to and weigh more than . Unlike ice pellets, hailstones are layered and can be irregular and clumped together. Hail is composed of transparent ice or alternating layers of transparent and