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Chauncy J. Schultz
and
Mark A. Askelson

1. Introduction Recent studies of tornado-producing environments have indicated that strong low-level wind shear and high values of near-surface moisture are critically important to tornadogenesis (e.g., Davies-Jones et al. 1990 ; Johns et al. 1993 ; Rasmussen and Blanchard 1998 , hereafter RB98 ). This is reflected in the study of parameters like 0–1-km bulk shear 1 and lifted condensation level (LCL) height, both of which have shown promise in discriminating between tornadic and

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Pamela Heinselman
,
Daphne LaDue
,
Darrel M. Kingfield
, and
Robert Hoffman

video-cued recall (described in section 3 ) allowed for a more detailed documentation of forecasters’ decision-making processes than the design used by Heinselman et al. (2012) . 2. Radar data and visualization Case selection criteria included sufficient longevity and temporal continuity in the data prior to tornadogenesis (for tornadic cases), minimal velocity aliasing, and storm location within a 120-km range of the PAR. The application of these criteria resulted in the selection of four

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Benjamin W. Green
,
Fuqing Zhang
, and
Paul Markowski

1. Introduction Landfalling tropical cyclones (TCs) have long been known to spawn tornadoes (e.g., Malkin and Galway 1953 ). Through the mid-1970s, research into TC tornadoes was limited to climatological studies. Relative to TC forward motion, the right semicircle ( Sadowski 1962 ) and then the right-front quadrant ( Pearson and Sadowski 1965 ) between 100 and 250 nautical miles (n mi, where 1 n mi = 1852 m) ( Smith 1965 ) from the center were identified as favorable areas for tornadogenesis

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Brian Tang
,
Matthew Vaughan
,
Ross Lazear
,
Kristen Corbosiero
,
Lance Bosart
,
Thomas Wasula
,
Ian Lee
, and
Kevin Lipton

, weakening occurs in regions of downslope flow. Orographically generated environmental cyclonic vertical vorticity anomalies, such as lee vortices and shear lines, may also increase the low-level vertical vorticity of a supercell ( Geerts et al. 2009 ; Markowski and Dotzek 2011 ). Baroclinic boundaries have been hypothesized to affect supercell evolution and tornadogenesis. Such boundaries may arise from synoptic fronts and outflow boundaries from prior convection. Additionally, boundaries may be

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Steven M. Martinaitis

et al. 2004 ). Supercellular reflectivity features like appendages, hook echoes, forward-flank notches, weak-echo regions (WERs), and bounded weak-echo regions (BWERs) were not always apparent and often subtle (e.g., Spratt et al. 1997 ; Devanas et al. 2008 ). Hook echoes or appendage signatures were observed prior to tornadogenesis in 75% of the tornadic events evaluated by Schneider and Sharp (2007) ; however, it was noted that relying on such signatures alone would result in missed tornadic

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Kenneth D. LaPenta
,
Lance F. Bosart
,
Thomas J. Galarneau Jr.
, and
Michael J. Dickinson

tornado developed within a synoptic-scale environment already favorable for tornadoes and severe thunderstorms, we will present some limited evidence that terrain-channeled low-level flow in north–south river valleys and the interaction of the isolated supercell responsible for the Mechanicville tornado with an overtaking squall line may have enhanced the likelihood of tornadogenesis. The paper is organized as follows. The synoptic overview appears in section 2 . The mesoscale environment is

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Brice E. Coffer
,
Matthew D. Parker
,
Richard L. Thompson
,
Bryan T. Smith
, and
Ryan E. Jewell

; Craven et al. 2004 ). The environmental proxies/ingredients currently used operationally to diagnose the probability of tornadogenesis originate from large datasets of proximity soundings derived from model analysis data ( Thompson et al. 2003 , 2007 , 2012 ), which provide superior temporal and spatial resolution compared to that of the upper-air observing network. The significant tornado parameter (STP) was developed as one of these tools to aid operational forecasters in the tornado forecasting

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Corey M. Mead

Brooks (1993) demonstrated that by tilting the baroclinically generated horizontal vorticity found within the rear-flank downdraft, positive vertical vorticity could be produced in the downdraft. Thus, the air reaching the ground within the downdraft, would already exhibit positive vertical vorticity before being ingested into the updraft. This established a possible physical link to the development of the low-level mesocyclone, a feature commonly observed prior to tornadogenesis. Brooks et al

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Zhiyong Meng
and
Dan Yao

) and (c) are also plotted in (b) and (d) for reference. An interesting result was that the tornado was spawned during the upward shrinking process of DRC1, and DRC1 continued to shrink upward after tornadogenesis ( Fig. 13b ). At 1336 LST, which was a couple of minutes before the first sign of tornado damage, the 50-dB Z isosurface shrunk upward while the 40- and 47-dB Z isosurfaces still remained near the ground. At 1342 LST, when the TVS was the strongest and the severe tornado damage started

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Ming Xue
,
Ming Hu
, and
Alexander D. Schenkman

matched an observed tornado was accurately simulated and the tornadogenesis processes were analyzed in detail. In this study, we examine the ability of a nonhydrostatic numerical weather prediction model in predicting the intensity of an observed tornado that was rated as a category 4 event on the Fujita scale (F4) and that developed within a supercell storm typical of the central and southern Great Plains of the United States. The case chosen is the tornadic supercell that occurred on 8 May 2003 in

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