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Roger Edwards

Member Since 14 Mar 2009
Offline Last Active Jun 21 2017 07:41 AM
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Topics I've Started

EJSSM 12.1: Damage Path Width and Discontinuity in 50 Tornado Tracks Through Forested...

27 February 2017 - 05:25 AM

EJSSM forum comments are welcome on this article by Zenoble and Peterson (2017):

 

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Abstract:

 

Tornado damage-path width is a necessary component for calculation of area impacted, which allows estimation of hazards.  To date, rarely has variation in damage path width or path discontinuity been a focus.  In this paper, using a damage threshold of >25% canopy damage, we quantify width and discontinuity in 50 tornado paths in forested areas.  Tornado-path starting and end points were overlaid on Google Earth imagery obtained ≤24 months after the tornadoes, and damage-path width (or absence of damage) was measured for severities >25% canopy loss, at fixed intervals.  Width was measured only where both sides of the damage path were clearly defined by forest tree damage, thus many points were excluded from our analysis.  Given our threshold level of forest canopy damage, no EF0 tornadoes showed remotely visible damage, and analyses were thus restricted to ≥EF1 tornado paths.  Variation in remotely visible damage width was quantified as coefficient of variation, which ranged from 0.227 to 0.852, with a mean of 0.531 among the 50 paths.  Discontinuity in remotely visible damage also varied among damage paths; up to 45% of the total number of measured points within a path lacked visible damage.  Almost 40% of tornado damage paths exhibited such discontinuity along 20% or more of their path length.  We suggest that the long, narrow EF-scale contours (particularly for ≥EF1) often reported after storm surveys may mask extensive width variation in severe damage and substantial portions of tornado paths with no severe damage.  


EJSSM 11.5: A Multi-Scale Analysis of the Atmospheric Conditions Associated with the D...

24 December 2016 - 08:27 AM

EJSSM forum comments are welcome on this article by Lanicci (2016):

 

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Abstract:

 

This case study describes a severe-storm event over Florida, Georgia, and South Carolina on 25 December 2006, with a particular focus on an F2 tornado that struck Daytona Beach, FL and caused over $50 million in damages.  The severe weather occurred over a 12-h period and was associated with a deep upper-level trough and surface front moving through the southeastern U.S.  Morning soundings over Florida showed low to moderate CAPE and strong vertical wind shear, consistent with seasonal composite tornadic soundings for the region.  A quasi-linear convective system moved onshore near Tampa during the midmorning hours, the northern half of which accelerated and produced bow echoes that resulted in two tornadoes and nontornadic wind damage over Pasco, Sumter, and Lake Counties between 1620 and 1725 UTC.  This portion of the line then moved into Volusia County and spawned F2 tornadoes in Deland and Daytona Beach after 1800 UTC.  Data from the Melbourne National Weather Service Forecast Office’s Weather Surveillance Radar-1988D (WSR-88D), Daytona Beach International Airport (DAB) Automated Surface Observing System (ASOS), and DAB Low Level Wind Shear Alert System (LLWAS) were integrated to analyze conditions at the east end of the DAB runway 7L/25R complex, where the tornado first appeared.  The LLWAS is normally used by air traffic control personnel for monitoring airport wind-shear conditions.  The 10-s LLWAS wind data filled critical temporal and spatial gaps in the WSR-88D and ASOS data, and captured evidence of strong winds and cyclonic curvature nearly coincident with the locations of the radar-identified velocity couplet and tornado itself.


EJSSM 11.4: Ensemble Forecasting of Return Flow over the Gulf of Mexico

09 August 2016 - 01:31 PM

EJSSM forum comments are welcome on this article by Lewis et al. (2016):

 

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Abstract:

 

Errors in operational forecasts of return flow events (RFEs) over the Gulf of Mexico have dictated the search for sources of these errors. Based on earlier studies, likely candidates for these errors are: incorrect parameterization of turbulent transfer processes at the air-sea interface, uncertain vertical motion above the mixed layer, and incorrect initial conditions. We investigate these possible sources of error by performing numerical experiments with a Monte Carlo ensemble prediction model applied to a well-observed case in February 1988. In essence, we examine uncertainty in prediction due to uncertainty in the model’s elements of control. A mixed-layer model with roughly 50 elements of control is used to determine forecast uncertainty due to initial conditions alone, boundary conditions alone, parameterization alone, as well as the full complement of uncertainty in these elements of control. The uncertainty is calculated at points along a predetermined outflow trajectory that originates over shelf waters in the northeastern Gulf, passes north of the Yucatan Peninsula, and terminates in the west-central Gulf—all points along the trajectory are characterized by convective heating at the sea-air interface. Results from the numerical experiments led to the following results: 1) parameterization of physical processes exerts the greatest influence on forecast uncertainty, and 2) the water-vapor mass in the mixed-layer column is uncertain by a factor of two at the trajectory’s terminal point. The latter result confirms forecasters’ long-held view that vapor return is the most suspect product in operational prediction of RFEs. In addition to these numerical experiments with the 1988 case, a recent RFE is examined in the context of operational model performance at the National Center for Environmental Prediction (NCEP). The paper ends with discussion of steps to be taken that hold promise for improved operational prediction of RFEs over the Gulf of Mexico.


EJSSM 11.3: The Sensitivity of Deep Ascent of Cold-Pool Air to Vertical Shear and Cold...

27 July 2016 - 11:36 PM

EJSSM forum comments are welcome on this article by Houston (2016).
 

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Abstract:

 

The tilting and stretching of solenoidally generated vorticity that is hypothesized to be a necessary
condition for supercell tornadogenesis is predicated on the presence of ascent of cold-pool air. Results are
presented from experiments designed to test the sensitivity of this ascent to the temperature deficit of the
cold pool and the environmental vertical shear. Experiments use idealized 2D numerical simulations
involving a density current and a parameterized non-rotating deep convective updraft. Experiments
conducted with only the density current demonstrate that simulated cold-pool upward motion generally
exhibits a highly correlated direct relationship to both environmental vertical shear and cold-pool
temperature deficit. Thus, despite increased negative buoyancy, colder cold pools are theoretically
characterized by faster ascent of cold-pool air. In the presence of the parameterized, non-rotating, deep
convective updraft, cold-pool upward motion is found to exhibit a strong linear relationship to both
environmental shear and cold-pool temperature deficit. A cold-pool tracer is also used to measure the
depth of transport of cold-pool air. Maximum tracer depth is found to increase linearly with environmental
vertical shear but is found to decrease with increasing cold-pool temperature deficit. These sensitivities are
attributed to the degree of phasing between deep positively buoyant ascent and the density current
dynamics: for stronger shear and smaller cold-pool temperature deficits, the deep updraft and the gust front
remain in close proximity, resulting in deep transport of cold-pool air.

 


EJSSM 11.2: Inferring the Severity of a Multicell Thunderstorm Evolving to Supercell,...

24 March 2016 - 11:16 AM

EJSSM forum comments are welcome on this article by Rigo and Pineda (2016).

 

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Abstract:

 

This study analyzes a long-lived thunderstorm with supercell characteristics that took place in the northeastern Iberian Peninsula on 5 July 2012. Severe weather features identified in Doppler radar and total lightning data have been used to infer the severity of this large-hail-bearing storm that substantially damaged local agriculture. Key elements identified in the radar product analysis were: relatively short development time, a long mature phase lasting >2 h, and high and sustained values for most of the radar parameters (reflectivity, vertically integrated liquid, echo tops), which showed an evolution from multicell to supercell structure. Nevertheless, the most significant patterns were the vertical lifting of the cell core, the three-body scatter spike, the bounded weak-echo region, and the anticyclonic rotation, observed in the Doppler velocity fields. Key features identified in the lightning analysis were: 1) the total lightning "jump" as an early sign for severity, 2) the low negative cloud-to-ground (CG) flash rate and 3) the low intensities in negative CG strokes and the regular rate of positive CG as indicators of complexity in the electrical structure. Finally, data strongly suggest the worst damage occurred when the thunderstorm was in its supercell stage. This case study presents one of the first documented supercells in the region.