Environmental conditions associated with nocturnal severe weather across the northern Plains

Near real-time predictability of severe weather for the purpose of issuing short-term convective warnings to save life and property can be difficult during daylight hours. This task is even more difficult when managing nocturnal convection. The enhanced complexity is generally due to a reduced amount of real-time feedback from spotters, as well as increased possibility that the planetary boundary layer has decoupled, leading to increased surfaced-based convective inhibition and reducing the threat of damaging winds and tornadoes. The distinction between environments capable of producing tornadoes and damaging winds during nocturnal hours versus circumstances where low-level inhibition is too large and only severe criteria hail is expected has further importance due to the increased risk to the public safety during these hours.

To help operational forecasters distinguish between these environments, nocturnal storm reports were compiled from 1997 through 2009 for tornadoes, hail, and wind in the northern Plains. These events were then categorized based on the number of reports, and if the event included tornadoes and damaging wind along with hail. Further discrimination was completed to isolate the events where nocturnal wind and tornadoes were more isolated versus widespread. North American Regional Reanalysis data composites of common convective elements were then developed to distinguish between these events. Further analysis of a select number of these events will be presented utilizing a high resolution convection-resolving model to assess to what degree these events can be forecast.