Two rounds of severe weather recently affected the Northeast. From April 14-15, 13 tornadoes touched down in the region - nine in Pennsylvania (two EF-2s, three EF-1s, and four EF-0s), two in Delaware (EF-2 and EF-1), and one each in New York (EF-1) and Maryland (EF-0). Then on April 19, two EF-2 and three EF-1 tornadoes moved through south-central Pennsylvania.
Damage from an EF-1 tornado in Union County, PA, on April 15. Image courtesy National Weather Service State College.
Of all the Northeast states, Pennsylvania averages the most tornadoes for April with two (1989-2013 data) and annually with 15 (1985-2014 data). The 14 tornadoes this month have made it one of the most active Aprils for tornadoes in Pennsylvania since records began in 1950. The EF-1 that trekked through Fulton County on the 19th was the county’s first April tornado and only its fifth tornado on record. With two tornadoes, Delaware has also had an active month. The state has had only five other April tornadoes, with the most recent in 1993. Delaware averages zero tornadoes in April and one annually.
Pennsylvania, New York, and Maryland average 1 or 2 tornadoes in April. Click to enlarge.
The April 14-15 outbreak was also unusual due to the time of day that many of the tornadoes touched down - in the early morning hours. Tornadoes can occur at any time of day, but most touch down in the afternoon and evening. That’s because daytime heating often contributes to thunderstorm formation, and in turn tornado activity. On April 14-15 there were favorable atmospheric conditions for the development of severe weather, including a strong cold front, wind shear, and warm, moist air.