82 Diurnal variations in severe weather forecast parameters of RUC-2 model-derived proximity environments associated with tornadoes from 2003-2011

Monday, 5 November 2012
Symphony III and Foyer (Loews Vanderbilt Hotel)
L. J. Reames, University of Oklahoma, Norman, OK; and J. M. Straka

A great number of studies have attempted to use different sizes and varieties of tornadic databases to quantify the typical near-storm pre-tornadic environment. Many databases, while significant in size, are limited in scope; some consider those tornadoes that occur between specific times of the day or during certain seasons only while others are limited in their geographical extent. The present study attempted to provide an overview of severe storm parameters from near-storm soundings of recent weak-to-strong (F1-F2) and very strong-to-violent tornadoes (F3+) that is geographically and seasonally expansive and split approximately evenly between daytime and nocturnal cases.

This study makes use of a database of Rapid Update Cycle (RUC-2) model-derived near-storm soundings for 198 significant (10+ mile track) (E)F1 to (E)F5 tornadoes. Each sounding was used to calculate eighteen severe storm parameters commonly used to forecast severe storm potential including Mixed-Layer Convective Available Potential Energy (CAPE), Mixed-Layer Convective Inhibition (MLCIN), surface to 1km Storm-Relative Helicity (SRH), and 0-3km CAPE. Because the RUC-2 is known to have difficultly accurately portraying surface temperature characteristics, each sounding was modified with surface temperature from the nearest surface observing station that was uncontaminated by the storm's precipitation. This method is similar to the procedure that the Storm Prediction Center uses to modify their mesoanalysis products.

The findings of the study suggest that 0-1km SRH is much higher at night for all tornadic intensities, but that considering plots of shear versus buoyancy parameters is more useful for determining between the tornadic intensities than any single parameter. The data also indicate that a combination of any shear parameter in the lowest 3km of the atmosphere, when combined DCAPE200, discriminate well between tornadic intensities at night. In addition, the data show that, when differentiating between environments that are supportive of nighttime versus daytime tornadoes, a combination of low level shear parameters and CAPE3km is the most useful.

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