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A Case Study of nonmesocyclone tornadogenesis along convergence boundaries: Northwest Texas 25 March 2007

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Title: A Case Study of nonmesocyclone tornadogenesis along convergence boundaries: Northwest Texas 25 March 2007


1
A Case Study of nonmesocyclone tornadogenesis
along convergence boundaries Northwest Texas 25
March 2007
  • Mark Conder and Todd Lindley - National Weather
    Service, Lubbock, Texas
  • James M. Caruso - National Weather Service,
    Wichita, Kansas
  • Jon Davies - Private Meteorologist, Wichita,
    Kansas

2
Introduction
National Weather Association 32nd Annual Meeting,
18 October 2007
  • On 25 March, two episodes of landspout
    formation occurred in conjunction with
    thunderstorm activity in northwest Texas
  • While the landspouts were short-lived and
    caused minimal damage (All rated F-0), the
    first round of landspouts occurred near the city
    of Lubbock thus were widely seen and
    received considerable media attention
  • A conceptual model developed by J. Caruso and
    J. Davis in 2005 describes an environment
    favorable for landspout development that appears
    to be consistent with the setup on this day
  • This study will examine how this event
    compares with the conceptual model, and
    explore several methodologies that may aid
    forecaster recognition of this type of
    landspout scenario

3
Landspout Conceptual Model
National Weather Association 32nd Annual Meeting,
18 October 2007
  • Landspout tornadoes differ from mesocyclonic
    ones in that the environmental wind shear
    is not sufficient for supercell development
    however, pre-existing wind shear boundaries can
    create low-level wind shear and thermal
    conditions that approach those associated with
    supercells
  • Typically, these tornadoes are short-lived and
    only produce EF0 to EF1 damage. However, on
    occasion they may produce EF2 to EF3 damage and
    last longer than 15 minutes
  • Caruso and Davies developed a conceptual model
    (NWA E-Journal, 1995) defining a set of
    common characteristics of the mesoscale
    environment
  • Slow-moving or stationary wind shift boundary
  • A surface heat axis intersecting the boundary
  • Steep low-level lapse rates, considerable
    low-level CAPE, and little CIN

4
National Weather Association 32nd Annual Meeting,
18 October 2007
Landspout Conceptual Model
Wakimoto and Wilson, 1989
5
National Weather Association 32nd Annual Meeting,
18 October 2007
Landspout Conceptual Model
Caruso and Davies, 2005
6
25 March Timeline and Map
National Weather Association 32nd Annual Meeting,
18 October 2007
15-17 UTC SW-NE oriented Sfc Boundary slowly
develops across the central South Plains.
Partial clearing results in a heat
axis developing parallel to this boundary
1706 UTC First cell becomes apparent via radar
1732 UTC First landspout reported southeast of
Lubbock
1732-1750 UTC Additional landspout, strong wind
reports
1800-2000 UTC Boundary accelerates N-NW as
thunderstorm outflows enhance the S-SE wind
along the boundary
2000-2200 UTC Boundary decelerates as it moves
into the northwest South Plains and encounters
an existing surface trough
2155-2215 UTC Additional landspouts are observed
in Castro, Lamb and Swisher Counties
7
25 March Timeline and Map
National Weather Association 32nd Annual Meeting,
18 October 2007
8
Synoptic Overview 500 hPa
National Weather Association 32nd Annual Meeting,
18 October 2007
9
Synoptic Overview 850-800 hPa
National Weather Association 32nd Annual Meeting,
18 October 2007
10
Model soundings Lubbock 15, 17 UTC
National Weather Association 32nd Annual Meeting,
18 October 2007
11
Visible Satellite Imagery with surface
plots/analysis
National Weather Association 32nd Annual Meeting,
18 October 2007
12
Radar Image LoopRound 1
National Weather Association 32nd Annual Meeting,
18 October 2007
13
Radar Image LoopRound 2
National Weather Association 32nd Annual Meeting,
18 October 2007
14
Assessing the Environment D2D
National Weather Association 32nd Annual Meeting,
18 October 2007
15
Assessing the Environment D2D
National Weather Association 32nd Annual Meeting,
18 October 2007
16
Assessing the Environment NAM
National Weather Association 32nd Annual Meeting,
18 October 2007
17
Assessing the Environment RUC
National Weather Association 32nd Annual Meeting,
18 October 2007
18
Assessing the Environment West Texas Mesonet
National Weather Association 32nd Annual Meeting,
18 October 2007
RELATIVE LINK
WEBSITE LINK
E LINK
D LINK
F LINK
G LINK
H LINK
R LINK
19
Summary
National Weather Association 32nd Annual Meeting,
18 October 2007
  • In general, the mesoscale environment in this
    case was very similar to the cases and
    conceptual model presented in Caruso and Davies
    2005.
  • The only significant departure was the
    relatively moist low-level environment
    resulting in reduced low lower MLLCL heights and
    a slight reduction in low-level lapse rates
    (7.5 C/km versus DALR).
  • The new NonSupercell Tornado Families in D2D
    provide several fields that can alert the
    forecaster to the potential for landspouts. Their
    usefulness is limited by the model
    resolution/general unpredictability of smaller
    scales.
  • Analyses from a mesonetwork can prove very
    useful to track the actual evolution of the
    important surface features. The paramount issue
    is how to get this information to the
    forecaster as quickly as possible.
  • WSR-88D strategy Watch for rapid cell
    development in the vicinity of the
    convergent boundary. GRL2 Analyst may be useful
    since the vertical growth of the storm can
    be more easily visualized.

20
Photographs
National Weather Association 32nd Annual Meeting,
18 October 2007
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