An active storm system moving east across the U.S., triggered a severe weather outbreak in the Midwest on the night of Tuesday, 5 February.

The driving force for the severe weather was the combination of a strong jet stream, unseasonably warm, moist air over the Midwest and an active cold front moving from the west. A warm and moist southerly airflow extended across the Midwest and Southeast States on Monday, 4 February following a warm front that tracked northward. Temperatures rose into the 70s and 80s Fahrenheit (20-30C) on Monday and Tuesday afternoon and due points reached the 60s (15-20C), indicating a very moist environment. On Tuesday afternoon/evening an active cold front crossed the Plains and in combination with the warm, moist airmass in place, produced a very unstable environment, capable of spawning severe supercell thunderstorms.

The severe weather extended from northeastern Texas to the lower Ohio River Valley, covering 9 states in total. Supercell thunderstorms spawned numerous fatal tornadoes, damaging winds and hail measuring up to the size of softballs.

Severe weather reports from the National Weather Service indicates there were 78 tornado reports, 220 wind reports and 119 hail reports. Tornadoes were reported in Tennessee, Arkansas, northern Mississippi and northern Alabama and there is confirmation of at least one tornado rated EF4 on the enhanced Fujita Scale in Alabama and numerous EF3 tornadoes through Tennessee, Arkansas and Alabama. It will take several more days until damage surveys are complete and the number and intensity of all the tornadoes is confirmed. Early evidence also suggests there were a few large, long-track tornadoes, most notably in Arkansas.

As was the case with the Midwest tornado outbreak in January, several temperature records were broken across the South prior to the severe weather, contributing to an ‘out of season’ tornado outbreak.

March and early April roughly mark the beginning of the spring severe thunderstorm season in North America. Severe thunderstorms are defined as those with hail at least 3/4 inch in diameter, winds 58 mph (93 km/hr) or greater or tornadoes. March/April is characterized by a rapid rise in tornado and hail activity, and the majority of tornadoes in the year occur between April and June. Geographically, the area of greatest activity moves over the course of a year. Over the winter months, activity is concentrated in the southeastern U.S., where the relatively warm Gulf of Mexico can help fuel thunderstorm development. The February 5, 2008 tornado outbreak is slightly further north than what is typically experienced at this time of year. Generally, as the year progresses, the area of peak activity expands northwards from the southeastern states, as the land surface begins to warm and the jet stream becomes established at more northern latitudes. It is not until late June and July that the Canadian Provinces experience their peak activity and this is only a fraction of the thunderstorm activity of Oklahoma or Texas during April and May. As cold air begins to progress south into the U.S. in autumn, thunderstorms again become more active in the Central U.S., with a second peak in tornado activity occurring during this time.

Summary

Hundreds of properties have been destroyed as a result of the severe weather outbreak and the death toll as of Thursday, 7 February stands at over 50 with hundreds more injured. At this time there is very little information regarding the exact number of properties damage but as damage assessments and the clean up operation continues over the next week the true extent and severity of this event is likely to emerge.

Contact:

Mark Prindle
TorranceCo
Old Chelsea Station
PO Box 11
New York, NY 10113
212-691-5860
mprindle@torranceco.com