In 2014, the American Society of Civil Engineers (ASCE), the Structural Engineering Institute (SEI) and the American Meteorological Society (AMS) undertook the effort of developing a standard for tornado wind speed estimation, which will officially standardize the EF-Scale, and introduce additional wind speed estimation methodologies. The "Easter Sunday" tornado that occurred on April 12, 2020, in Monroe, Louisiana, provided an opportunity to use a draft version of the EF-Scale method that is being prepared for this ASCE/SEI/AMS standard to assess damage because multiple reconnaissance teams were deployed to document the damage using different remote-sensing data sets. The data collected from street-level imagery and uncrewed aerial systems were used in this study to compare the 2006 EF-Scale and draft standard, as well compare the damage evaluations of buildings and trees across different evaluators. Statistical analysis was conducted for the differences between assessments of buildings inspected, the majority of which were one- and two-family residences. Correlation values in the damage evaluation were found to be low between evaluators when buildings had nonstructural damage (broken windows or loss of roof covering or siding), and the analysis highlighted the limitations of each of the remote-sensing data sets. A major recommendation of this study is to omit resistance indicators from the description of the degrees of damage in the new ASCE/SEI/AMS EF-Scale method, to further limit subjectivity.

Weather radars provide surveillance and warning systems that increase public safety and security. The United States is home to one of the most powerful and advanced weather radar networks in the world, which could still be improved in a number of ways, including improved coverage through additional supplemental radars. In October 2016, the University of Louisiana Monroe began operating a polarimetric S-b and Doppler weather radar (KULM, Monroe, Louisiana) in an area without extensive low-level coverage. Here, we evaluate the impact of this installation and operation of the KULM radar on local report climatology, operational meteorology, and casualty impacts of tornadoes over the last 10 years divided into an early (2012-16) and late (2017-21) period. Results indicate more than a sevenfold increase in the number of annual tornado reports across the KULM area between the early and late period, a decrease in KULM area false alarm rate, and a nearly unchanged KULM area probability of detection over time, as well as a decline in the KULM area annual casualty rate since the installation and operation of the radar. Holistically, these findings suggest additional investment in radars that provide supplemental low-level coverage have the potential to improve National Weather Service warning activities all while providing significant value to the public that extends beyond the individual tornado hazard.

Quasi-linear convective systems (QLCSs) are responsible for approximately a quarter of all tornado events in the United States, but no field campaigns have focused specifically on collecting data to understand QLCS tornadogenesis. The Propagation, Evolution, and Rotation in Linear Storms (PERiLS) project was the first observational study of tornadoes associated with QLCSs ever undertaken. Participants were drawn from more than 10 universities, laboratories, and institutes, with over 100 students participating in field activities. The PERiLS field phases spanned 2 years, late winters and early springs of 2022 and 2023, to increase the probability of intercepting significant tornadic QLCS events in a range of large-scale and local environments. The field phases of PERiLS collected data in nine tornadic and nontornadic QLCSs with unprecedented detail and diversity of measurements. The design and execution of the PERiLS field phase and preliminary data and ongoing analyses are shown.

This case study analyzes a tornadic supercell observed in northeast Louisiana as part of the Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE) on 6-7 April 2018. One mobile research radar (SR1-P), one WSR-88D equivalent (KULM), and two airborne radars (TAFT and TFOR) have sampled the storm at close proximity for ;70 min through its mature phase, tornadogenesis at 2340 UTC, and dissipation and subsequent ingestion into a developing MCS segment. The 4D wind field and reflectivity from up to four Doppler analyses, combined with 4D diabatic La-grangian analysis (DLA) retrievals, has enabled kinematic and thermodynamic analysis of storm-scale boundaries leading up to, during, and after the dissipation of the NWS-surveyed EF0 tornado. The kinematic and thermodynamic analyses reveal a tran-sient current of low-level streamwise vorticity leading into the low-level supercell updraft, appearing similar to the streamwise vorticity current (SVC) that has been identified in supercell simulations and previously observed only kinematically. Vorticity dy-namical calculations demonstrate that both baroclinity and horizontal stretching play significant roles in the generation and am-plification of streamwise vorticity associated with this SVC. While the SVC does not directly feed streamwise vorticity to the tornado-cyclone, its development coincides with tornadogenesis and an intensification of the supercell's main low-level updraft, although a causal relationship is unclear. Although the mesoscale environment is not high-shear/low-CAPE (HSLC), the updraft of the analyzed supercell shares some similarities to past observations and simulations of HSLC storms in the Southeast United States, most notably a pulse-like updraft that is maximized in the low-to midlevels of the storm.

On 12 April 2020, a tornadic quasi-linear convective system (QLCS) produced two EF-3 tornadoes in Ouachita Parish, Louisiana in close proximity to instrumentation operated by the University of Louisiana Monroe’s (ULM) Atmospheric Science program. In addition to the in situ environmental information, a high-resolution aerial damage survey was conducted by the ULM Unmanned Aerial Systems program. In this paper, these datasets are used to provide a comprehensive environmental and storm-scale analysis of the tornadic QLCS through northern Louisiana. In addition, we discuss the importance of aerial damage surveys, and how Doppler radar-derived tornado intensity estimates compared to the damage survey.

The Sand Mountain and Lookout Mountain Plateaus in northeastern Alabama have been established as a regional relative maximum in tornadogenesis reports within the southeastern United States. Investigation of long-term surface datasets has revealed (i) stronger and more backed winds atop Sand Mountain than over the Tennessee Valley, and (ii) measured cloud-base heights are lower to the surface atop Sand Mountain than over the Tennessee Valley. These observations suggest that low-level wind shear and lifting condensation level (LCL) height changes may lead to conditions more favorable for tornadogenesis atop the plateaus than over the Tennessee Valley. However, prior to fall 2016, no intensive observations had been made to further investigate low-level flow or thermodynamic changes in the topography of northeastern Alabama. This paper provides detailed analysis of observations gathered during VORTEX-SE field campaign cases from fall 2016 through spring 2019. These observations indicate that downslope winds form along the northwest edge of Sand Mountain in at least some severe storm environments in northeastern Alabama. Wind profiles gathered across northeastern Alabama indicate that low-level helicity changes can be substantial over small distances across different areas of the topographic system. LCL height changes often scale to changes in land elevation, which can be on the order of 200–300 m across northeastern Alabama.

In October 2016, the University of Louisiana Monroe (ULM) began operating a polarimetric S-band Doppler weather radar to help close the low-level radar coverage gap across northern Louisiana by increasing the quantity of data sampled below 3.0 km AGL. Data are delivered in near-real time to local National Weather Service (NWS) Weather Forecast Offices to help meteorologists accomplish their mission of protecting life and property. The inclusion of ULM radar data into NWS operations has led to improved detection of severe and hazardous weather across northern Louisiana. This paper details how the ULM radar has been incorporated into NWS operations, the improvement in operational radar coverage, and the challenges of using a non-NWS radar in the NWS operational setting.

On 4 June 2013, a military chaff release occurred near Huntsville, Alabama, within the University of Alabama in Huntsville (UAH) mesoscale network. This event was unusual because the chaff remained in the atmosphere-maintaining a radar echo on nearby weather radars-for nearly 10 h after the initial release. This paper examines the radar evolution of the chaff event, supplemented by environmental observations using the UAH profiling equipment. Additionally, unique operational considerations faced by the National Weather Service Weather Forecast Office in Huntsville are addressed.

The transition region of a winter storm affected northern Alabama on 1 February 2007, and was observed by the University of Alabama in Huntsville (UAH)/WHNT-TV Advanced Radar for Meteorological and Operational Research (ARMOR) dual-polarization C-band radar and the UAH Mobile Integrated Profiling System. This allowed for observations of the changing temperature and humidity profiles with time as precipitation transitioned from snow, to sleet, to freezing rain, and eventually to rain—as the atmosphere warmed with time. During the period of freezing rain and rain, pockets of mixed-phase precipitation continued to be observed via ARMOR, indicating the height and/or depth of the melting level varied across the area. Vertical velocity and signal-to-noise ratio data from the wind profiler also are examined as precipitation type changed. The observations allow for explanation of the large-scale and microphysical processes occurring in this transition region.

By many metrics, the tornado outbreak on 27 April 2011 was the most significant tornado outbreak since 1950, exceeding the super outbreak of 3–4 April 1974. The number of tornadoes over a 24-h period (midnight to midnight) was 199; the tornado fatalities and injuries were 316 and more than 2,700, respectively; and the insurable loss exceeded $4 billion (U.S. dollars). In this paper, we provide a meteorological overview of this outbreak and illustrate that the event was composed of three mesoscale events: a large early morning quasi-linear convective system (QLCS), a midday QLCS, and numerous afternoon supercell storms. The main data sources include NWS and research radars, profilers, surface measurements, and photos and videos of the tornadoes. The primary motivation for this preliminary research is to document the diverse characteristics (e.g., tornado characteristics and mesoscale organization of deep convection) of this outbreak and summarize preliminary analyses that are worthy of additional research ...

Cold season tornadic outbreaks occur with regularity in the southeastern United States; however, detailed analyses of parent supercell storms in the cold season environment (often low CAPE, high shear) are scarce. This is often because storms do not always move close enough to radars for a comprehensive single-Doppler analysis and significant topography or trees in the Southeast make it difficult for mobile radars to operate, thus limiting dual-Doppler coverage. However, during the Super Tuesday tornado outbreak of 5-6 February 2008, two tornadic supercell storms passed within 30-40 km of the Weather Surveillance Radar-1988 Doppler (WSR-88D) sites in Memphis and Nashville, Tennessee (KNQA and KOHX, respectively). The relative steadiness of these storms during passage, along with the large motion vector (from the southwest at 2025 m s (1)), allowed the application of a synthetic dual-Doppler (SDD) analysis. As such, a detailed analysis of these storms was completed, including examinations of low-level circulations, updraft strength and location, as well as retrievals and evaluations of perturbation pressure and the vertical pressure gradient. This study presents one of the first comprehensive analyses of cold season supercells using only one Doppler radar. Additionally, the relative success and failures of using the SDD technique on supercell storms are discussed. Major findings for the primary case include the updraft maximizing at a very low height (3.0 km AGL), and weak pressure forcing within the rear flank resulting in a nonexistent rear-flank downdraft (RFD).

The environmental set-up for cool season quasi-linear convective systems (QLCS) is one that is also often conducive to wave generation, such as internal gravity waves, ducted gravity waves, solitary waves or Kelvin-Helmholtz waves. These waves are usually observed interacting with the linear system as distinct horizontal lines of weak to moderate reflectivity or areas of enhanced reflectivity that appear to be larger pieces of energy moving through the atmosphere. The reflectivity features are observed propagating through the QLCS faster than the background wind. Numerous cases of potential interactions have been observed via the WSR-88D network in the Southeastern United States. Three recent cases are presented here.

Airborne measurements of hydrogen peroxide and its partitioning between the aqueous and gas phases were conducted during studies of wintertime orographic clouds at temperatures ranging between −9° and −24°C. A subset of the derived values of the H2O2 Henry's law coefficient, based on measurement of gas‐phase H2O2 and the physical properties of the cloud, were found to agree with laboratory measurements extrapolated to the cloud temperature. Disparities between the derived and temperature‐extrapolated values were also observed, but this was attributed to overestimates of the in‐cloud H2O2 mixing ratio that result from solute H2O2 volatilization on the reverse‐flow air sample inlet during cloud droplet impaction and freezing. This hypothesis is supported by the fact that the derived Henry's law coefficients which exhibit agreement with the temperature‐extrapolated values were conducted using a narrower inlet which intercepts less cloud water. Also discussed are vertical profiles of gaseous H2O2 within and above a cloud‐capped boundary layer and in‐cloud measurements which reveal that H2O2 scavenging by ice hydrometeors is minimal in comparison to uptake by an equivalent mass of liquid cloud droplets.