National Weather Center Convection/NWP Seminar Series
Organizers: Dr. Louis Wicker, Ryan Sobash
This seminar is held Fridays at 3:00 p.m. in NWC 5600 during the regular OU spring and fall semesters.
|01/24/14||Jill Hardy||SoM||Probabilistic Flash Flood Forecasting using Stormscale Ensembles
Flash flooding is one of the most costly and deadly natural hazards in the US and across the globe. The loss of life and property from flash floods could be mitigated with better guidance from hydrological models, but these models have limitations. For example, they are commonly initialized using rainfall estimates derived from weather radars. This introduces a problem for forecasting flash floods because the time interval between observations of heavy rainfall and a flash flood can be on the order of minutes, particularly for small basins in urban settings. Increasing the lead time for these events is critical for protecting life and property. Therefore, this study advances the use of quantitative precipitation forecasts (QPFs) from the stormscale CAPS ensemble system into a distributed hydrological model setting to yield basin-specific, probabilistic flash flood forecasts (PFFFs).
Rainfall error characteristics of the individual CAPS members are first diagnosed and quantified in terms of structure, amplitude, and location (SAL; Wernli et al., 2008). To compute the PFFFs, we considered the June 14, 2010 Oklahoma City flash flood event. This new approach is shown to: 1) identify the specific basin scales within the broader regions that are forecast to be impacted by flash flooding based on cell movement, rainfall intensity, duration, and the basin’s susceptibility factors such as initial soil moisture conditions; 2) yield probabilistic information about the forecast hydrologic response; and 3) improve lead time by using stormscale NWP ensemble forecasts.
|03/14/14||Timothy Humphrey||SoM||Developing a methodology for the automated retrieval of azimuthal shear associated with tornadic circulations
The Multi-Year Reanalysis of Remotely Sensed Storms is a joint venture between the National Severe Storms Laboratory and National Climatic Data Center to reprocess radar data for the entire country during the lifespan of WSR-88D. This dataset provides several data mining opportunities through the use of the Warning Decision Support System Integrated Information (WDSS-II) software. This presentation summarizes a methodology for the automated retrieval of azimuthal shear utilizing WDSS-II tools. Results are presented for 443 tornado events that occurred in 2010 and 2011. Potential applications of the azimuthal shear values, areas of future research, and possible improvements to the methodology will also be discussed.
|03/21/14||No seminar||Spring Break|
|03/28/14||Matt Staley||SoM||A Revised Conceptual Model of Convective Initiation Associated with Drylines
Identifying the exact time and location of convective initiation often is a challenge for meteorologists due to an incomplete understanding of the complex physical processes involved. By successfully monitoring contributing factors for convective initiation at a high spatial and temporal resolution, forecasters can formulate a more accurate conceptual model of the environment leading to increased situational awareness. In order to demonstrate the value of high resolution analysis, four case studies of convective initiation in Oklahoma were selected for examination. Three cases from 2010 including May 10th, May 19th, and April 6th were chosen as well as a fourth case from 20 May 2013. Analyses were created using ADAS and 3DVAR by assimilating surface mesonet observations and radar data with a time-interpolated NAM forecast background field at a temporal resolution of 5 minutes and a grid spacing of 400 meters.
All four cases featured dryline convection of various intensities. A more detailed conceptual model of the dryline was produced including the presence of a “mixing line” marked by a sharp gradient in equivalent potential temperature east of the primary dryline. This additional surface feature appeared to play a significant role in the initiation and maintenance of convective cells within and in the vicinity of the dryline zone. The value of these high resolution analysis products was displayed through the ability to diagnose contributing factors for convective initiation and identify locations where convection would eventually occur.
|04/04/14||Terra Thompson||SoM||Multi-Scale Data Assimilation of the 13 June 2010 Tornadic Supercell Storm Environment during VORTEX2
The success of ensemble data assimilation (hereafter DA) at convective-scales is limited by a number of challenges, including the difficulties associated with accurately analyzing mesoscale phenomenon in the storm environment. A promising new technique combines radar DA with simultaneous assimilation of conventional observations, hereafter referred to as multi-scale DA. Multi-scale DA is applied to the 13 June 2010 case during VORTEX2. On 13 June a cold pool from overnight convection created an outflow boundary that was located near the Oklahoma-Texas Panhandle border in the afternoon. New convection developed along a cold front in the Texas Panhandle. The sub-severe convection slowly moved to the northeast and a cell moved over the intersection of the two boundaries, intensified, gained supercell characteristics, and became tornadic. This case represents a complex mesoscale environment and storm evolution that was not captured well with conventional observations or WSR-88D radars. Thus, it is difficult to analyze and predict without the use of multi-scale DA.
A framework for multi-scale DA is developed to improve forecasts of the mesoscale storm environment and convection. The sensitivity to the background ensemble is investigated by comparing the storm environment after four days of DA cycling, to the storm environment initialized on the day of the event. The impacts of hourly multi-scale DA cycling on the day of the event are compared to conventional six hourly analysis cycles. The value of radar DA in hourly DA cycling is also investigated. Lastly, the impact of the storm environment on convective forecasts will be discussed.
|04/11/14||Lee Carlaw||SoM||Investigating the Impacts of Assimilating Non-Conventional Surface Observations on High-Resolution Analyses and Forecasts
With recent advances in computing capabilities, research efforts have focused increasingly on the influence of radar data on high-resolution analyses and forecasts. Comparatively few studies have investigated the impacts of surface observations on storm-scale simulations. Even fewer have attempted to determine the effects of incorporating non-conventional stations that are owned by private companies, the public, or non-governmental agencies. In an attempt to improve our current mesoscale observing capabilities, the National Research Council recently proposed a plan for the development of a nationwide Network of Networks that would integrate many disparate non-conventional systems into a coordinated, national observing infrastructure.
In order to evaluate the potential value added by assimilating non-conventional observing systems, several Observing System Experiments (OSEs) were conducted on 400-m resolution analyses and forecasts of a tornadic supercell that developed during the evening of 15 May 2013 to the southwest of the Dallas-Fort Worth Metroplex. In this case study, the addition of thermodynamic data from non-conventional surface observations within the storm inflow proved fundamentally important to forecasts of the storm evolution. Additionally, a continuous, cycled analysis system is developed in order to test the longer-term impacts of assimilating non-conventional surface data on hourly 4-km analyses beginning on 1 March 2014. Verification of these analyses show consistent improvements when non-conventional data are included in the assimilation scheme.
|04/18/14||Brittany Dahl||SoM||Sensitivity of Vortex Production to Small Environmental Perturbations in High-Resolution Supercell Simulations
Studies have indicated that errors in the initial conditions of atmospheric models propagate toward both larger and smaller scales of motion, which limits the range of practical predictability in numerical forecasts. With short-term, storm-scale prediction to play an increasingly important role in tornado warning operations (e.g., Warn-on-Forecast), it is beneficial to understand the relative impact of errors in the background mesoscale environment on storm features associated with tornadogenesis.
To investigate the effect of mesoscale errors on low-level mesocyclone-scale vortex development in simulated supercells, perturbations were randomly drawn from typical 1-hour forecast errors observed from the 13 km RUC in Cintineo and Stensrud (2013) and applied to the 29 May 2004 Geary, OK sounding. Two sounding ensembles were created by scaling these errors to 10% and 25% of the original magnitude. These soundings were then used to initialize horizontally homogeneous environments for 41 idealized simulations at a resolution of 100 m. The vortex detection and classification (VDAC) algorithm outlined in Potvin (2013) was used to identify vertically continuous mesocyclone-scale vortices. An intra- and inter-ensemble comparison of the spatial distribution of detected vortices, timing of detections, and vortex strength is conducted, as well as analysis of the relationship between initial environmental conditions and vortex characteristics.
|04/25/14||Kevin Haghi||SoM||Identifying and characterizing atmospheric bores during IHOP_2002
How familiar are we with the behavior of atmospheric bores? An investigation of the International H20 Project (IHOP_2002) provides conflicting findings to previous work, along with new ideas about how to treat the nature of bores. A systematic study categorize fine-line boundaries identified in the nocturnal and near nocturnal environment (22-12 UTC), lead by radar images coupled with the available Multiple Antenna PRofiler (MAPR), surface observations and soundings. Over one month of data provides 143 fine-line boundaries, 65 of which are consistent with atmospheric bores; this is in conflict to the Wilson and Roberts (2006) study of radar fine-lines. Meanwhile, pure density currents that are not associated with generating bore-like features are relatively rare (8 cases out of 143). Moreover, atmospheric bores were visible most frequently over the Texas-Oklahoma panhandle and the southern stretch of Kansas. Radar images seem to suggest that these are in phase with the surface frontal boundaries, but out of phase with the maximum in rainfall accumulation during the same period.
Atmospheric bores, although identified in multiple previous case studies, assumed two dimensionality about the atmospheric bore fronts. Bootstraps of the mean of fine-line boundary rotations reveal a 2σ deviation from 0, suggesting atmospheric bores and density currents frequently exhibit clockwise rotations and three dimensionality of bores seems more appropriate. Additionally, according to radar, with only 25% of density current duration explainable by the bootstrapped atmospheric bores indicate that atmospheric bores are surviving longer and later into the night. Discussion ensues to the nature of applying convective and hydraulic theory to atmospheric bores.
|05/02/14||Race Clark||SoM||Flash Flooding Case Study: 31 May 2013 Oklahoma City, OK
A severe weather outbreak on 31 May 2013 brought heavy rains, large hail, tornadoes, and flash flooding to central Oklahoma. In all, fourteen people lost their lives due to flash flooding, thirteen of these in Oklahoma County. This was the deadliest flash flooding event in the state of Oklahoma since the Tulsa Memorial Day floods of 1984. Most of the flash flooding deaths can be attributed to the multi-hazard nature of the event; people chose to take shelter in storm-water control and routing structures to avoid what was perceived to be an imminent tornado. Reports from local media, social media, and official sources are used to create detailed analyses of where, when, and how fatalities and injuries occurred due to swiftly moving waters. Additionally, a detailed analysis of the nearly $17 million in damage that occurred due to the high waters is presented. Traffic counts from the Oklahoma Department of Transportation indicate that Oklahoma City traffic volumes on 31 May 2013 were extremely heavy compared to historical norms.
A meteorological and hydrological synopsis of the conditions leading up to the flash flooding is provided. High-resolution numerical weather prediction was successful at generally delineating the risk of heavy rainfall and attendant flash flooding. Operational flash flood guidance tools failed to correctly identify the areas of the most significant flooding impacts. However, the National Severe Storms Laboratory's FLASH system provided an accurate picture of where and when the flash flooding was most significant.
Subscribe to the listserv for this seminar series here:
To schedule a seminar, send your talk title (or a working title) to "louis.wicker at noaa dot gov" and "rsobash at ou dot edu". Seminar dates towards the end of the semester tend to fill up quickly, so reserve early! Unless you are a graduate student doing your required departmental seminar, your seminar need not fill the entire hour, nor be carefully polished. We encourage presentations (short or long) on works in progress!
To those presenting, e-mail your abstract to the organizers, as well as Marcia Pallutto (SoM), no later than one week before your seminar. The abstract will be placed in the weekly seminar e-mail and on this webpage.
For accommodations based on disability, or more details, please contact the School of Meteorology at 325-6561. Visitor parking is available for all University visitors. However, faculty/staff/students must have a current multi-purpose parking permit. Additional parking is available at the Lloyd Noble Center for those individuals who do not have a parking permit. OU ID must be presented at security desk.
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