Sunday, 22 January 2012
An Early Season Nocturnal Colorado Tornado
Hall E (New Orleans Convention Center )
Forecasting nocturnal tornadoes has proved to be an extremely difficult process; currently the process of operational forecasting is often piloted by results that are biased toward daytime tornadoes. Tornadoes, in general, vary according to the diurnal cycle and, at times, annual cycle, in a spatial fashion. Potential factors that deem nocturnal tornadoes different than those that occur in the daytime may include the variance of storm inflow, behaviors of the low-level jet (LLJ), and/or ENSO climate patterns. The Holly, Colorado tornado may provide some insight into the dynamics and environment of nocturnal tornadogenesis.
As a whole, the Holly tornado was an unusual nighttime event. Based on climatology, nocturnal tornadoes during the month of March occur in the southeast region, which makes Colorado an exclusive outlier. Some anomalous conditions that were present in Colorado during this time include warmer than normal surface temperatures, position of the jet stream, and ENSO climate patterns. Conditions that were linked to tornadogenesis in Holly included a strong thermal ridge, low-level divergence, and a strong closed low pressure system over the central Rockies. Analysis of the Holly case and others suggest that existing tornado climatologies may be misleading for forecasting nocturnal tornadoes.