Alan Gerard

“Bookend Vortex” Induced Tornadoes along the Natchez Trace

Abstract This study focuses on the evolution of the northern end of a bow echo that moved across parts of southwest Mississippi on 8 May 1995. A well-defined, cyclonically rotating “comma head echo” developed north of Natchez, Mississippi, and moved northeast for about 120 km (75 mi) before dissipating. The circulation associated with this comma head echo passed through several diameter changes during which the diameter varied between that of a classic mesocyclone and that more typical of a “bookend vortex.” The circulation and a strong rear inflow jet helped spawn small tornadoes (F0–F2) in Claiborne County, Mississippi, and wind damage in western Hinds County, Mississippi. The observed damage path from the tornadoes was more than 8 km (5 mi) long. For much of the track, the tornadoes paralleled the Natchez Trace, a scenic federal highway that extends from Natchez to Nashville, Tennessee.

User perception and interpretation of tornado probabilistic hazard information: Comparison of four graphical designs

Effective design for presenting severe weather information is important to reduce devastating consequences of severe weather. The Probabilistic Hazard Information (PHI) system for severe weather is being developed by NOAA National Severe Storms Laboratory (NSSL) to communicate probabilistic hazardous weather information. This study investigates the effects of four PHI graphical designs for tornado threat, namely, four-color, red-scale, grayscale and contour, on users perception, interpretation, and reaction to threat information. PHI is presented on either a map background or a radar background. Analysis showed that the accuracy was significantly higher and response time faster when PHI was displayed on map background as compared to radar background due to better contrast. When displayed on a radar background, grayscale design resulted in a higher accuracy of responses. Possibly due to familiarity, participants reported four-color design as their favorite design, which also resulted in the fastest recognition of probability levels on both backgrounds. Our study shows the importance of using intuitive color-coding and sufficient contrast in conveying probabilistic threat information via graphical design. We also found that users follows a rational perceiving-judging-feeling-and acting approach in processing probabilistic hazard information for tornado.

Effective Method to Convey Threat Information for Tornado: Probabilistic Hazard Information vs. Deterministic Hazard Information

Effective conveyance of hazard information to society is crucial for enhancing public preparedness for the uncertainty involved in the occurrence of tornadoes. The WarnGen system is currently used for issuing deterministic severe weather warnings. To provide society with probabilistic weather information, researchers at The National Severe Storm Laboratory are developing a tool called Probabilistic Hazard Information (PHI). The current study reports an experiment intended to figure out if including information about the uncertainty of a tornado occurrence provided through PHI would help people understand the weather information better and take more appropriate protective action. Our group also wanted to investigate if including probabilistic information about the surrounding area of the target zone would be effective in people’s decision making regarding their safety. The results show that including information about uncertainty in the weather information makes it more effective than the deterministic hazard information in terms of perception, cognition, and protective actions of recipients. Also, presence of information about the target zone’s surrounding area does not have any significant effect on their decision making.

Development of a Human–Machine Mix for Forecasting Severe Convective Events

AbstractProviding advance warning for impending severe convective weather events (i.e., tornadoes, hail, wind) fundamentally requires an ability to predict and/or detect these hazards and subsequently communicate their potential threat in real time. The National Weather Service (NWS) provides advance warning for severe convective weather through the issuance of tornado and severe thunderstorm warnings, a system that has remained relatively unchanged for approximately the past 65 years. Forecasting a Continuum of Environmental Threats (FACETs) proposes a reinvention of this system, transitioning from a deterministic product-centric paradigm to one based on probabilistic hazard information (PHI) for hazardous weather events. Four years of iterative development and rapid prototyping in the National Oceanic and Atmospheric Administration (NOAA) Hazardous Weather Testbed (HWT) with NWS forecasters and partners has yielded insights into this new paradigm by discovering efficient ways to generate, inform, and ut...

The effect of providing probabilistic information about a tornado threat on people’s protective actions

National Weather Service issues deterministic warnings in a tornado event. An alternative system is being researched at National Severe Storms Laboratory to issue Probabilistic Hazard Information (PHI). This study investigated how providing the uncertainty information about the tornado occurrence through PHI changes people’s protective actions. In an experiment, visual displays of the probabilistic information and deterministic warnings were presented to fifty participants to report their expected protective actions in different scenarios. It was found that the percentage of people who expected to immediately take shelter right after receiving the weather information increased exponentially as their proximity to the threat decreased. When there was more chance that the information about occurrence of a particular tornado was false rather than true, in scenarios that the likelihood of the threat occurrence was less than 50%, providing it through PHI lowered the percentage of people who immediately took shelter. The ordinal logistic regression models showed that the probability of taking protective actions significantly changes by providing the uncertainty information when people have less than 20xa0min lead time before getting impacted by the threat. When the lead time is less than 10xa0min, the probability of immediately taking shelter increases to 94 from 71%, and when the lead time is more than 10 but less than 20xa0min, that probability increases from 53 to 70%, if they are provided with the probabilistic information. Presenting the likelihood of any tornado formation in the area did not have significant effect on the people’s protective actions.

Bridging Operational Meteorology and Academia through Experiential Education: The Storm Prediction Center in the University of Oklahoma Classroom

AbstractDuring the 2014–15 academic year, the National Oceanic and Atmospheric Administration (NOAA) National Weather Service Storm Prediction Center (SPC) and the University of Oklahoma (OU) School of Meteorology jointly created the first SPC-led course at OU focused on connecting traditional theory taught in the academic curriculum with operational meteorology. This class, “Applications of Meteorological Theory to Severe-Thunderstorm Forecasting,” began in 2015. From 2015 through 2017, this spring–semester course has engaged 56 students in theoretical skills and related hands-on weather analysis and forecasting applications, taught by over a dozen meteorologists from the SPC, the NOAA National Severe Storms Laboratory, and the NOAA National Weather Service Forecast Offices. Following introductory material, which addresses many theoretical principles relevant to operational meteorology, numerous presentations and hands-on activities focused on instructors’ areas of expertise are provided to students. Top...

Analysis of the Record Mesosnowfall Event of 1997 in Central Mississippi

Abstract Although rare, heavy snowfalls in the southern United States have significant impact and are often associated with distinct surface low pressure systems. However, the central Mississippi record snowfall event of 14 December 1997 displayed mesoscale characteristics and was caused by a rapidly intensifying upper-level system with no surface reflection. Record amounts of unforecast snowfall of up to 8 in. (20.3 cm) occurred. A synoptic and diagnostic analysis of the event determined significant jet streaks, the existence of a middle- and upper-level moisture pool, and a deformation zone with high-level frontogenesis led to the snowfall despite rather unremarkable surface conditions. The system was fully investigated in terms of atmospheric and model diagnostics in an effort to provide clues for an improved forecast. A hindcast simulation of the event using the Pennsylvania State University–National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5) revealed that the use of a meso...