Forecasting Tornado Outbreaks vs. Derecho in the Northeast

Introduction

Forecasting Tornado Outbreaks vs. Derechos in the Northeast 

Introduction

Data and Methodology

Patterns

Storm Relative Wind Flow

References

 A study was undertaken to compare the environments that produce significant tornado outbreaks with environments that produce derechos in the northeast United States.  It should be noted that there is some overlap in the two types of events. Some derechos produced weak tornadoes. Also, bow echoes and squalls lines were observed during some tornado events. For example, on 30 May 1998 a devastating tornado struck Spencer, South Dakota as more than 20 tornadoes hit the northern Plains States. During the early morning of 31 May 1998, the same system produced a derecho across the Great Lakes Region. Then, during the afternoon and evening of 31 May, over 30 tornadoes (some F3) struck the Northeast. Large bow echoes were noted at times during this tornado outbreak. The 21 cases in this study were all major severe weather events. This study was designed to help forecasters better determine whether a major severe weather event will include strong and violent tornadoes, or whether straight line winds associated with a derecho will be the main form of severe weather.