Overview

A tornado outbreak with a total of 26 reported tornadoes occurred across Texas on 29 December 2006. Twenty-two of the tornadoes occurred within the area of responsibility of the Fort Worth/Dallas Weather Forecast Office. This event was unprecedented with regard to the number of tornadoes that occurred during a single episode in north Texas in the month of December. 

The outbreak  is documented by providing a brief overview of the tornadoes and tornado warnings, a discussion of the pre-storm environment on the synoptic scale, an analysis of the mesoscale and thermodynamic environment before and during the tornado occurrences, and a radar analysis of the most significant supercell storms. 

As a slow-moving, intense upper-level cyclone moved across the southwestern United States, an unseasonably warm and moist air mass spread north from the Gulf of Mexico into much of central and eastern Texas.  Tornadic supercells developed near a warm front in an environment with steep mid-level lapse rates, moderate surface-based instability and extremely strong low-level vertical wind shear.  All of the supercells developed well east of the occluded front.

Excerpts From the Paper

On 29 December 2006, a rare event unfolded in north Texas, as a tornado outbreak produced 22 tornadoes across the Fort Worth/Dallas (FWD) Weather Forecast Office (WFO) county warning area (CWA).  Only two other wintertime tornado outbreaks have been documented across north Texas since 1950.  The 29 December 2006 tornado outbreak produced more tornadoes than any other winter tornado outbreak case since 1948.  

Twenty-two of the 26 tornadoes that were reported across Texas on 29 December 2006 occurred across the FWD CWA, affecting 12 of the 46 counties that comprise the CWA.   The tornado outbreak on this day was the largest across north Texas since 25 April 1994 when 24 tornadoes were reported in the FWD CWA.  The Figure below depicts the tracks of all 22 tornadoes across the FWD CWA.    

The potential for severe weather existed on 29 December 2006 as a powerful upper-level trough across the southwestern United States and northern Mexico moved slowly toward west Texas.  An occluded front was progressing eastward across west Texas, with an east-west oriented warm front moving north through the eastern half of the state.  As late as six hours prior to the onset of the outbreak, the jet stream and frontal pattern appeared to favor the development of a severe, linear convective system along the occluded front.  However, tornadic supercell thunderstorms developed in several north-south bands east of the occluded front in a zone of pronounced low-level thermal advection. 

Despite extensive cloud cover during the day, surface temperatures warmed within the zone of pronounced low-level thermal advection.  Low-level winds remained strong from the southeast during the day in an environment characterized by intense vertical wind shear.  The combination of high values of low-level convective available potential energy and large wind shear values supported strong low-level mesocyclones and tornadic development.  Of the 22 tornadoes that occurred in the FWD CWA, three were rated F2 on the legacy Fujita Scale, causing significant structural and tree damage, several injuries, and one fatality.

The paper examines the tornado outbreak on 29 December 2006 and explores the synoptic and mesoscale factors that combined to create this event.  Section 2 provides an overview of the tornadoes including a detailed summary of the tracks and damage produced by the three F2 tornadoes.  Section 3 reviews the synoptic pattern of the event and compares this event with other cold-season and warm-season tornadic episodes.  Similarities and differences in the low-level and surface patterns with other cold-season tornado events are also compared in Section 3.  A comprehensive review of the mesoscale factors and thermodynamic environment that were critical to the outcome of this event are discussed in Section 4.  Finally, Section 5 provides an in-depth radar analysis of the storms that produced the F2 tornadoes.  

The entire manuscript contains 34 color tables, figures, and illustrations that explain all aspects of the event in detail.  

Download the entire manuscript at the link below – 52 pages, 5.5 mb PDF file 

OVERVIEW AND ANALYSIS OF THE 29 DECEMBER 2006 TEXAS TORNADO OUTBREAK