Mid-October 2007 Tornado Outbreak - Meteorological Synopsis

Meteorological Synopsis

A deep low pressure system (with a pressure of 977 mbar at its peak) moved across the Pacific Coast on October 15 and then crossed the Rockies during the following day and touched out some moist air from the Gulf of Mexico, major source for storm development and intensification. Not part of the main outbreak, 3 tornadoes were reported, during the overnight hours of October 16 towards October 17, across Randall County, Texas south of Amarillo on October 16 with 1 of them confirmed as a high EF1. That tornado caused damage to trees, fences, power poles, steel pipes, trailers and barns.

The next day a dry line, which separates the drier air from the more moist and humid air, formed ahead of the cold front across the Texas and Oklahoma Panhandles and tracked eastward. The high humidity levels with dew points in the 70s°F (low 20s°C), temperatures that in many areas were near 80°F (27°C), strong wind shear and the presence of the dry line helped developed the instability to produced severe thunderstorms across the Midwest and Southern Plains on October 17.

A moderate risk for severe weather was issued by the Storm Prediction Center two days prior to the event. The storm then moved across the most of the Midwest on October 18, where a moderate risk was in effect also for two days for most of Illinois, Indiana and parts of Kentucky, although the moderate risk was revised further to the south and east to include western Ohio, western Tennessee, southeastern Missouri, northeastern Arkansas and a larger portion of Kentucky while Michigan and Wisconsin were no longer under a moderate risk. A slight risk of severe weather was forecast for a very large area from beyond the Canadian border to the Florida Panhandle and Mobile Bay. Dew points above 70°F (21°C) were reported well into the Ohio Valley, and dew points above 60°F (16°C) were reported as far north as northern Ontario.

The outbreak was expected to continue into October 19 east of the Appalachians, however, extensive cloud cover prevented any significant severe storms from developing although several wind reports were reported in Pennsylvania, New Jersey and Massachusetts. The storm then moved out into the Atlantic Ocean on October 20.