A climatology of significant (F2-F5) nocturnal tornadoes in the contiguous United States between 2004 and 2006 shows that environments deemed by previous climatologies as unfavorable for late afternoon/early evening tornadogenesis are in fact conducive to significant nocturnal tornadogenesis. These nocturnal environments may be characterized by marginal convective instability with shallow stable boundary layers. Substantial low-level shear, storm relative environmental helicity (SREH), and exceptionally strong nocturnal low-level jets stand out as the most common features of significant nocturnal tornadoes, and have utility in distinguishing environments of weak nocturnal tornadoes from environments of significant nocturnal tornadoes. Analysis of the data gathered in the climatology shows that the suggestions of existing tornado climatologies are inadequate and even misguiding for forecasting nocturnal tornadoes. Several recommendations for operational forecasting of nocturnal tornadoes are made based on the results of this climatology.
Supplementary URL: http://journals.ametsoc.org/doi/abs/10.1175/2009WAF2222294.1?prevSearch=&searchHistoryKey=