Dual-Wavelength Polarimetric Radar Analysis of the May 20th 2013 Moore, OK, Tornado

Alexandra Borunda —  California State University at Fullerton
Mentors: Casey Griffin & Dr. David Bodine (OU/ARRC)

Link to Abstract and Paper

What is already known:

• Tornadic debris signatures can confirm the presence of a tornado and provides information about the amount of damage occurring.
• Debris scattering characteristics were found to be different at S- and C- band.

What this study adds:

• Observational confirmation of differences in the debris scattering characteristics between S- and X- band polarimetric radar observations.
• The first time S- and X- band tornadic debris signatures have been compared, providing others an opportunity to compare our results with previous S- and C- band studies.
• A better understanding of the observed scattering characteristics of tornadic debris signatures between S- and X- band is obtained from a violent tornado that lofts an abundance of debris.

Illustrating Predictability for Nocturnal Tornado Events in the Southeastern United States

Ryan Bunker — University of Oklahoma
Mentors: Dr. Ariel Cohen (NOAA/SPC), Alan Gerard (NOAA/NSSL), Dr. Kim Klockow (CIMMS/NSSL), and John Hart (NOAA/SPC)

Link to Abstract and Paper

What is already known:

• Substantial vulnerabilities to severe weather and tornadoes exist during the night when visibility is limited and when people are asleep.
• Previous work using the Statistical Severe Convective Risk Assessment Model (SSCRAM) has shown the utility of environmental parameters to predict severe weather occurrence.

What this study adds:

• This study utilized SSCRAM to show that strong vertical shear is useful in predicting nocturnal tornado events in the southeast United States.
• Furthermore, the coastal region subset within the southeast U.S. offers worse predictability when compared to the rest of the CONUS.

An East Coast Winter Storm Climatology and Projected Future Trends

Lena Dziechowski — University of Massachusetts Lowell
Mentors: Dr. Elinor Martin (OU/SoM) and Liz DiGangi (OU/CIMMS & NOAA/NSSL)

Link to Abstract and Paper

What is already known:

• East coast winter storms coincide with increasing extreme precipitation, wind, and storm surge events
• Large observed annual and decadal variability of frequency and intensity of storms.
• Most models project a decrease in frequency, however changes in intensity are less certain.
• Studies use only mean sea level pressure or 850-hPa vorticity to track cyclones.

What this study adds:

• Historical observations show increase in maximum wind and no change in minimum pressure. However, models underpredict the maximum wind in the historical period.
• Models project a decrease in frequency, no change in intensity.
• A tracking algorithm with a model dependent wind threshold should be tested for cyclone identification.

Analyzing the Sensitivity of Hail Prediction to Model Grid Spacing

Tyler Green —  Embry-Riddle Aeronautical University, Daytona Beach
Mentors: Dr. Amy McGovern (OU/SoM & OU/CS) & Dr. Nate Snook (OU/CAPS)

Link to Abstract and Paper

What is already known:

• Explicit hail prediction using high resolution models will be imperative for the Warn on Forecast vision
  
• For ensemble modeling with grid spacing of less than1 kilometer, little to no research has been done on sensitivity of explicit hail prediction to grid spacing.

What this study adds:

• Systematic differences in hail and hail related fields were identified as grid spacing was varied in three ensembles using 500, 250, and 100m horizontal grid spacings.
• Updraft distributions and near storm environment can be ruled out as a likely cause for differences found in the explicitly predicited hail field, suggesting a microphysical budgeting analysis needs to be investigated to account for differences found.

Impact of Different Microphysical Schemes and Additional Surface Observations on NEWS-e Forecasts

Francesca Lappin —  Florida State University
Mentors: Dr. Dusty Wheatley & Dr. Kent Knopfmeier (OU/CIMMS & NOAA/NSSL)

Link to Abstract and Paper

What is already known:

• The NOAA Warn-on-Forecast (WoF) Project seeks to enhance warning lead times and reduce false alarm rates for hazardous weather using ensemble storm-scale data assimilation and prediction systems such as the NSSL Experimental Warn-on-Forecast System for ensembles (NEWS-e).
• The NSSL Experimental Warn-on-Forecast System for ensembles (NEWS-e) assimilates radar, satellite, and conventional (e.g., surface) data, and the resultant storm-scale analyses are used to generated new 0-3 h probabilistic forecasts two times an hour.
• In 2017, the NEWS-e began assimilating surface observations from ASOS sites (in addition to Oklahoma Mesonet). Also, the microphysical scheme was changed from the Thompson (partial two-moment) to the NSSL two-moment.

What this study adds:

• In this study, when verifying simulated thunderstorm rotation objects, the assimilation of surface observations from ASOS sites produced forecasts with consistently higher probability of detection (POD) scores, by as much as 20% at early forecast times.
• The change from a partial two-moment (Thompson) to a full two-moment microphysical scheme provided similar improvements to the POD scores.
• Using different choices for microphysics show that the Thompson simulations produce too many model grid points with accumulated rainfall in the 0-.5 in range, while the NSSL 2-moment simulations produce too many grid points for rainfall amounts exceeding 0.5 in.

Stratospheric Polar Vortex Trends of the Twentieth and Twenty-First Centuries and an Assessment of the CMIP5 Historical Ensemble

Carly Narotsky — University of North Carolina at Asheville
Mentor: Dr. Jason Furtado (OU/SoM)

Link to Abstract and Paper [PDF]

What is already known:

• The position and strength of the Northern Hemisphere stratospheric polar vortex can be used as indicators of winter temperatures at the middle and high-latitudes.
• Previous studies have found a directional shift in the position of the stratospheric polar vortex away from the pole and toward the Eurasian continent. One study has linked this trend to Arctic sea-ice loss and increased snow cover over the Eurasian continent associated with anthropogenic climate change (Zhang et al. 2016), while another has attributed the trend to internal variability (Seviour 2017).
• Sudden stratospheric warming events, which are associated with a breakdown of the stratospheric polar vortex, are not projected to increase in frequency during the twenty-first century. However, a climatological equator-ward shift of the vortex centroid is projected (Mitchell et al. 2012).

What this study adds:

• Analysis of polar cap height (PCH) during the twentieth century reveals high variability throughout the century, with multi-decade time periods sustaining high PCH, and multi-decade time periods sustaining low PCH.
• The CMIP5 Historical ensemble does not adequately reproduce the stratospheric vortex trends of the past. Only two models out of nine in the ensemble reproduce the directional shift of the stratospheric polar vortex toward the Eurasian continent, and there is high spread among the model results for all diagnostics.
• With low variability among the models, stratospheric geopotential heights are projected to rise in both the middle and high-latitudes during the twenty-first century, leaving projections of polar vortex strength unclear.
• With some variability among the models, the position of the stratospheric polar vortex is projected to shift toward Northeast Asia during the twenty-first century.

General Hail Occurrence Frequency in Convective Storms Using mPING Data

Stormi Noll — University of Nevada Reno
Mentor: Dr. Kim Elmore (OU/CIMMS & NOAA/NSSL)

Link to Abstract and Paper [PDF]

What is already known:

• There is no method to discriminate between small hail and large raindrops using radar products
• If hail is often present, the quantitative precipitation estimation (QPE) will be negatively impacted
• The meteorological Phenomena Identification Near the Ground (mPING) smart phone application allows public citizens to submit reports of the weather occurring at their location.

What this study adds:

• This study helps to determine the extent to which small hail is expected to be present in convective storms
• It confirms that hail cannot be detected based on composite reflectivity alone
• mPING reports can be used to better understand hydrometeor characteristics.

How Forecasters Anticipate Nocturnal, Cool-Season Southern Tornado Events

David Nowicki — University of Mississippi
Mentor: Dr. Ariel Cohen (NOAA/SPC & OU/SoM), Alan Gerard (NOAA/NSSL), Kim Klockow (UCAR), and John Hart (NOAA/SPC)

Link to Abstract and Paper [PDF]

What is already known:

• Steps towards the probabilistic forecast and warnings of Warn-on-Forecast have been taken using a variety of tools, including improved radar detection and novel ensemble numerical weather prediction models.
• Nocturnal, cool-season tornado events in the southeast United States are difficult to forecast/warn for, for a plethora of reasons.
• The public in this area of the country are particularly vulnerable to these events and would benefit by having a longer warning lead time.

What this study adds:

• This study offers insight into what tools/measures forecasters are using currently when in the kinds of situations described above.
• Forecasters’ beliefs regarding the potential utility of the Statistical Severe Convective Risk Assessment Model as well as forecasters’ propensity to use such a model, were it available, are shown.
• The existence of a gap between forecasters’ general knowledge and their ability to use SSCRAM to improve their forecasting accuracy in these situations shows a need to further examine current and potential use of conditional probabilities in forecasting.

Future Projections of Heat Waves and Cooling Degree Days in Large Cities Across the South-Central United States

Melanie Schroers — Texas A&M University, Commerce
Mentors: Dr. Derek Rosendahl, Dr. Adrienne Wootten, and Dr. Renee McPherson (SC CSC)

Link to Abstract and Paper [PDF]

What is already known:

• Heat is one of the leading causes of weather related mortality in the United States.
• Studies have shown that heat waves will increase in frequency, duration, and intensity under anthropogenic climate change.
• Heat waves lead to increased cooling requirements, mortality, and power outages.

What this study adds:

• In large cities in south-central United States the number of heat waves per year will more than triple by the late century, 2075-2099.
• The need for cooling, measured by cooling degree days, in these large cities is shown to increase up to 85%.
• Cities should start planning for future impacts from increased heat related events.

Difficulties With Classifying and Analyzing the Low Level Jet in a Convection Allowing Ensemble

Emily Tinney —  Central Michigan University
Mentor: Dr. James Correia, Jr. (OU/CIMMS & NOAA/SPC)

Link to Abstract and Paper [PDF]

What is already known:

• The low level jet can act to increase vertical wind shear, heat, and moisture in the overnight hours, therefore having important implications for storms in the Great Plains.
• William Bonner used a 2-year jet climatology in 1968 to create a jet classification method that is still commonly used today.
• Bonner's low level jet criteria specifies thresholds of wind speed at the jet maxima and wind shear above that maxima which must be met to be classified as a low level jet.

What this study adds:

• The Bonner classification method does not properly classify the low level jet in cases with a strong synoptic wind field that makes the shear criteria difficult to meet.
  
• Since storms tend to form in non-quiescent conditions, a better low level jet classification method is required to analyze the relationship between storms and the low level jet in a convection allowing ensemble.
  
• Future low level jet classification studies should focus on using parameters such as storm relative helicity and wind shear below the wind maximum, rather than the wind shear above.

Statistical Analysis of Heatburst Events Across Oklahoma From 1997-2016

Robert Van Kleeck — Lyndon State College
Mentor: Dr. Brad Illston (OCS)

Link to Abstract and Paper [PDF]

What is already known:

• Heatbursts occur quite often across Oklahoma in the late spring and early summer, and have been known to cause millions of dollars in damage
• Previous studies identified heatbursts over the Oklahoma Mesonet using a simple three-step threshold, along with subsequent manual analysis to eliminate drylines and other undesirable thermodynamic perturbations

What this study adds:

• Starting with a slightly modified three-step threshold, a Dew Point Depression Ratio (DPDR) was used to automatically isolate heatburst events with no need for manual inspection of each detection
• Comparison of detections to manual analysis shows that the ratios are highly accurate at sequestering heatbursts

Assessment of Dual-Polarized Radar Coverage in the Terminal Airspaces of Commercial Airports

Jacqueline Waters — University of Hawai'i at Manoa
Mentors: Dr. Heather Reeves & Alicia Keys (OU/CIMMS & NOAA/NSSL)

Link to Abstract and Paper [PDF]

What is already known:

• Weather accounts for a large number of aircraft accidents with a wide range in variety.
• Previous studies have focused on Federal Aviation Administration (FAA) core 30 airports, non dual-polarization radars, and radar uncertainty.
• Various radar algorithms are being or have been developed today in hopes of mitigating threats in the terminal airspace.

What this study adds:

• Assessment of all 337 conus commercial airports which will be compiled into a webpage for the FAA.
• Analysis on four deficiencies regarding radar coverage in the terminal airspace including limited nearby coverage, beam blockage by terrain or other ground-based features, cone of silence issues, and limited upstream coverage.
• Case study analysis shows how two common radar problems, beam broadening and overshooting, vary depending on airport to radar distance, VCP mode, and beam blockage.