Squall Line Research Articles

Impact assessment of the West African monsoon on convective precipitations over the far north region of Cameroon

Squall lines observed over the sahelo-sudanese regions are responsible for most of the annual rainfall recorded in these regions. They originate from the development of convective processes embedded in the Mesoscale Convective Systems (MCS). The impact assessment of the West African Monsoon (WAM) on the development of squall lines in the sahelo-sudanese regions, particularly the far north region of Cameroon is studied. In this study, the Tropical Rainfall Measuring Mission data (TRMM 3A12 and 3B43) and ERA5 reanalysis data from 1998 to 2008 have been used. The technique used is based on the use of the Climate Data Operator (CDO) software and the NCAR command language (NCL). Analysis of these data shows that the seasonal distribution of winds from the saharan heat-low and the Saint Helena high is the dominant atmospheric dynamics associated with the disturbances behind the development of squall lines. This distribution makes it possible to specifically draw up the evolution of the InterTropical Discontinuity (ITD) on the African continent, and thus, highlight the contribution of the WAM on precipitation in the far north region of Cameroon. This study is performed to contribute to the prediction of hydro-meteorological phenomena to improve disaster risks management associated with floods and landslides in this region, the most vulnerable in Cameroon.

Impact of Different Double-Moment Microphysical Schemes on Simulations of a Bow-Shaped Squall Line in East China

Four typical double-moment cloud microphysical schemes (Milbrandt, Morrison, NSSL and WDM6) in WRF (Weather Research and Forecasting) are used to investigate the impact of the different schemes on the simulation of a straight squall line evolving into a bow-shaped one in East China on 15 April 2016. Although simulations with Milbrandt, Morrison and WDM6 schemes can produce bow-shaped squall lines, only the WDM6 scheme can simulate the evolution process of the straight squall line to a bow-shaped one well. The simulation results with the NSSL scheme produce a broken straight squall line. The possible reason is that the range and intensity of cold pools and the rear inflows are different among the four schemes when the observed squall line evolves into a standard bow-shaped squall line. The mixing ratio and number concentration of rain water with the WDM6 scheme is largest in strong convective areas, and the cold pool and rear inflow are also strongest among the four schemes. Compared with the WDM6 scheme, the mixing ratio and number concentration of rain water are less with the Milbrandt and Morrison schemes. Also, the cold pool and rear inflow with the Milbrandt scheme are weaker than for the WDM6 scheme but stronger than those with the Morrison scheme. The rainwater mixing ratio is very low and no obvious cold pool and rear inflow exist with the NSSL scheme.

An improvement of wind gust estimate (WGE) method for squall lines

Severe wind gusts produced by squall lines are difficult to monitor and forecast. This paper assessed and improved the physics-based Brasseur WGE (wind gust estimate) method for diagnosing wind gust of squall lines by coupling the WGE methods with the WRF (Weather Research and Forecasting) model. The simulation results show that the Brasseur WGE method accurately captured the strong gust feature with 32 m·s−1 maximum wind speed during the disastering Shipwreck event occurred over Yangtze River on 1 June 2015, but overestimated the extended area of severe gust speeds. Analysis of the kinematic structure and boundary-layer conditions of the squall line confirmed the theoretical applicability of the Brasseur WGE method for squall lines. A novel gust-front-area limiting method was introduced to modify the Brasseur WGE method, which effectively reduces its gust wind overestimation area. Furthermore, five squall line events occurred in the middle China during 2021 were simulated to test the modified WGE method and the results exhibit significant improvements to the wind gust forecasts, with an average false alarm rate decreased from 0.89 to 0.54, and the critical success index(CSI) increased from 0.1 to 0.4.

Evaluating an Ice Crystal Trajectory Growth (ICTG) Model on a Quasi‐Idealized Simulation of a Squall Line

AbstractA major challenge in numerical weather prediction models is the ability to accurately simulate the microphysical properties and growth of ice hydrometeors in clouds. Eulerian bulk microphysics schemes in these models tend to obscure the properties and evolution of individual ice crystals, often resulting in inaccurate simulations of storm structures. To address this issue, this study presents a novel ice crystal trajectory growth (ICTG) model that simultaneously grows and advects individual ice crystals while tracking their evolving properties along their trajectories. The model is evaluated on a 3D quasi‐idealized leading‐convective, trailing‐stratiform squall line simulation. The ICTG model successfully produced a spatial distribution of ice crystal trajectories consistent with the simulated reflectivity structure of the storm above the melting level. Smaller initialized crystals (d ≤ 0.1 mm) were largely transported to the anvil and the trailing stratiform region. One primary trajectory involved sustained growth in the stratiform mesoscale updraft for ∼1.5 hr, resulting in a density reduction down to 600 kg m−3, a final particle size greater than 0.9 mm, and potential branching. In contrast, larger initialized crystals (d ≥ 0.5 mm) collected more rime and fell out primarily in the leading convective line. The ICTG model's realistic production of varied crystal growth properties owing to differences in transport and initial size suggests that it can be a valuable tool for learning about ice microphysical processes in a variety of cold cloud systems.

Comparison of infrasound emissions from tornadic and non-tornadic storms

At a previous ASA meeting (Spring 2019), some results corresponding to application of maximum likelihood estimation with the complex Wishart distribution to direction-of-arrival of infrasound from tornadic storms were presented. In this presentation, updated results are presented and compared with estimation of direction-of-arrival of infrasound from two non-tornadic storms that were measured with the same infrasound arrays. One of these storms was similar to the tornadic storm in that it consisted of numerous isolated storm cells with frequent lightning. The other storm was significantly different in that it was a well-organized squall line that produced only limited lightning. The tornadic storm yielded very well-defined direction-of-arrival tracks in contrast to the non-tornadic storms.

Tropical cyclogenesis associated with premonsoon climatological dryline over the Bay of Bengal

Tropical cyclones of the Bay of Bengal (BoB) that formed near the synoptic-scale dryline usually intensified over a distance of 600–800 km within 3 days and caused severe destruction after landfall. High-resolution simulations of very severe cyclonic storms in association with dryline indicate that the meridional shear aids in the development of a linear-shaped group of convective cells that mature as an east–west oriented quasi-linear convective system (QLCS) within the boundary between the dry-moist air masses. The leading edge deep convections are supported by low-level moist southwesterly inflow; however, the typical mid-level mesoscale convective vortex (MCV) associated with these QLCS is unremarkable due to a very narrow trailing stratiform region within the QLCS. Supercells are likely to be organized within the QLCS due to extremely unstable atmospheric conditions resulting from a strong vertical shear of 27–39 m s−1 between 0 and 6 km and large convective available potential energy of > 3000 J kg−1. The vertical shear veering with height causes several numbers of low-level mesovortices having diameters less than 10 km at the leading edge in the different convective stages of the QLCS. The dryline aloft in the BoB produces horizontal positive shear vorticity of the order 10–5 s−1 with higher values in the levels 850–600 hPa. The advection of intense cloud-scale cyclonic mesovortices (~ 10–3 s−1) assists and enhances a cyclonic vortex to the rear side of the QLCS that performs as an MCV for cyclogenesis over the BoB.

A Study on Local‐Scale Thermal and Dynamical Mechanisms in the Initiation of a Squall Line Under Weak Forcing

AbstractA convective system was initiated under weak forcing on the plains near Beijing on the afternoon of 26 June 2009 and developed into a squall line that resulted in heavy precipitation. Prediction of the convective initiation (CI) of the system was challenging due to the lack of precursors detectable by conventional observation networks. In this study, we investigated the CI mechanism using high‐resolution analyses obtained from the Variational Doppler Radar Analysis System via the assimilation of radar and dense surface observations. It was found that the CI was resulted from the interactions of a local cold air mass and the outflows from a weakened storm propagating from the nearby mountains. The cold air mass built up an unstable condition and veered air flow to form a local convergence zone in which moisture was accumulated. New convection was triggered as a result of strengthened convergence when the outflows from the dissipating storm approached the existing convergence zone. To confirm the critical role played by the local cold air mass, sensitivity experiments were conducted using WRF‐FDDA data assimilation and forecast system. The results suggested that the local cold air mass along with the southerly environmental wind and storm outflows exerted a dominant influence on the CI.

Impacts of Coastal Terrain on Warm-Sector Heavy-Rain-Producing MCSs in Southern China

Abstract Warm-sector heavy rainfall in southern China refers to the heavy rainfall that occurs within a weakly forced synoptic environment under the influence of monsoonal airflows. It is usually located near the southern coast and is characterized by poor predictability and a close relationship with coastal terrain. This study investigates the impacts of coastal terrain on the initiation, organization, and heavy rainfall potential of MCSs in warm-sector heavy rainfall over southern China using quasi-idealized WRF simulations and terrain-modification experiments. Typical warm-sector heavy rainfall events were selected to produce composite environments that forced the simulations. MCSs in these events all initiated in the early morning and developed into quasi-linear convective systems along the coast with a prominent back-building process. When the small coastal terrain is removed, the maximum 12-h rainfall accumulation decreases by ∼46%. The convection initiation is advanced ∼2 h with the help of orographic lifting associated with flow interaction with the coastal hills in the control experiment. Moreover, the coastal terrain weakens near-surface winds and thus decreases the deep-layer vertical wind shear component perpendicular to the coast and increases the component parallel to the coast; the coastal terrain also concentrates the moisture and instability over the coastal region by weakening the boundary layer jet. These modifications lead to faster upscale growth of convection and eventually a well-organized MCS. The coastal terrain is beneficial for back-building convection and thus persistent rainfall by providing orographic lifting for new cells on the western end of the MCS, and by facilitating a stronger and more stagnant cold pool, which stimulates new cells near its rear edge.

A momentum-balance theory for the updraft structure in density currents analogous to squall lines

A momentum-balance theory for the orientation of updrafts in density currents is developed for understanding squall-line–shear interactions. The motivation arises from studies showing the diagnostic limitations of the vorticity-balance theory by Rotunno et al. (1988) (RKW theory) under varying shear profiles, together with the flow-force balance constraint (FFB) which determines the shear-layer depth in optimal density currents. Considering that the FFB is derived from the horizontal momentum equation, momentum-balance concepts are explored as an alternative to RKW theory, by assuming that the updraft’s slope is determined by the balance between advective tendencies of inflowing air and the work done by pressure perturbations within the denser fluid. Density currents were simulated under diverse shear and buoyancy profiles. Results show that momentum-balance effectively diagnoses the updraft’s slope at low and mid-levels in experiments contemplating both “classic” c-ΔU variations, as well as changes to the shear and buoyancy vertical profiles. It is also found that cases with stronger system-relative inflow tend to produce deeper lifting of near-surface environmental air, notwithstanding the updraft’s slope. RKW theory’s quantitative criterion (c/ΔU) is not as effective at diagnosing the updraft’s slope nor the depth reached by near-surface parcels, although c/ΔU provides guidance for the updraft’s slope at upper levels. This result justifies a reinterpretation of c/ΔU as a measure of the impacts of wind velocities aloft on the updraft

Assimilation of Polarimetric Radar Observation with GSI Cloud Analysis for the Prediction of a Squall Line

Assimilation of Polarimetric Radar Observation with GSI Cloud Analysis for the Prediction of a Squall Line

Comparative study of the simulation and mechanism of two different severe thunderstorms embedded in a squall line in North China

Based on a cloud-permitting numerical simulation carried out using the Weather Research and Forecasting Model, version 4.1.5, a squall line (SL) system accompanied by severe thunderstorms in North China in July 2019 was simulated. Both the observation and simulation showed that the convective organizational modes of the thunderstorms experienced three main stages: a quasi-linear (QL), bow echo (BE) and SL stage. Across these three stages, the thunderstorms consisted of two different convective systems. One was a thunderstorm with severe wind gusts (SWGs), which was concentrated in the BE and SL stages, and the other was a thunderstorm without gales but that featured high frequency lightning (HFL), which initiated and enhanced in the QL and SL stages, respectively. In the BE stage, SWGs began to extend backwards from the apex of the bow structure. In the SL stage later, the extent of SWGs increased significantly and dominated over a wide range behind the convective line as the convection nearly died out. Further analysis showed that the features and formation mechanisms of the SWG system were significantly different between the two stages. During the BE period, SWGs were mainly caused by the downdrafts in the convective core, which could be attributed to the formation and development of the horizontal vortex pair in the lower level. In the SL stage, however, SWGs mainly attributed to the sinking of the rear inflow, which was associated with the wide extent of negative buoyancy in the uneven convective environment, enhanced by the evaporation of the rainwater near the surface. HFL enhanced strongly on an extreme cold surface in the SL stage as the thunderstorm grew vigorously. The outflow along the edge of the cold dome converged with the front inflow and continuously triggered convection. The development and the interaction between the multiple convective cells triggered lightning, which was enhanced by the strong condensation heating in the storms.

Assimilation of Polarimetric Radar Observation with GSI Cloud Analysis for the Prediction of a Squall Line

Assimilation of Polarimetric Radar Observation with GSI Cloud Analysis for the Prediction of a Squall Line

Multi-Scale Interaction between a Squall Line and a Supercell and Its Impact on the Genesis of the “0612” Gaoyou Tornado

The interaction between a squall line and a supercell and its impact on the genesis of a tornado that occurred in Gaoyou, Jiangsu Province, China on 12 June 2020 were analyzed using multi-source observations. The tornado formed as the result of an intensified meso-γ supercell in a favorable large-scale environment. The supercell developed in front of a squall line and slowly intensified after its formation. Due to its small size and weak intensity, the supercell did not produce any severe weather before the approaching of the squall line. As the squall line entered its mature stage with the formation of a well-organized bow echo, the supercell in front of the bow echo began to rapidly intensify and finally led to the tornado touchdown. The analysis of mesoscale and storm-scale wind fields indicated that the bow echo of the approaching squall line modified the kinematic fields near the supercell in such a way that was favorable for the intensification of the supercell. The interaction between the squall line and the supercell may have played a critical role in the occurrence of this tornado.

Multiscale Aspects of the 26–27 April 2011 Tornado Outbreak. Part II: Environmental Modifications and Upscale Feedbacks Arising from Latent Processes

Abstract One of the most prolific tornado outbreaks ever documented occurred on 26–27 April 2011 and comprised three successive episodes of tornadic convection that culminated with the development of numerous long-track, violent tornadoes over the southeastern United States during the afternoon of 27 April. This notorious afternoon supercell outbreak was preceded by two quasi-linear convective systems (hereinafter QLCS1 and QLCS2), the first of which was an anomalously severe nocturnal system that rapidly grew upscale during the previous evening. Here in Part II, we use a series of RUC 1-h forecasts and output from convection-permitting WRF-ARW simulations configured both with and without latent heat release to investigate how environmental modifications and upscale feedbacks produced by the two QLCSs contributed to the evolution and exceptional severity of this multiepisode outbreak. QLCS1 was primarily responsible for amplifying the large-scale flow pattern, inducing two upper-level jet streaks, and promoting secondary surface cyclogenesis downstream from the primary baroclinic system. Upper-level divergence markedly increased after QLCS1 developed, which yielded strong isallobaric forcing that rapidly strengthened the low-level jet (LLJ) and vertical wind shear over the warm sector and contributed to the system’s upscale growth and notable severity. Moreover, QLCS2 modified the mesoscale environment prior to the supercell outbreak by promoting the downstream formation of a pronounced upper-level jet streak, altering the midlevel jet structure, and furthering the development of a highly ageostrophic LLJ over the Southeast. Collectively, the flow modifications produced by both QLCSs contributed to the notably favorable shear profiles present during the afternoon supercell outbreak. Significance Statement The tornado outbreak that impacted the United States on 26–27 April 2011 was part of an extended outbreak that produced 343 tornadoes and numerous fatalities. This paper is Part II of a study that describes the meteorological factors supporting such a prolific event. Herein we investigate the convectively forced environmental modifications that occurred during a 36-h period encompassing three successive convective episodes. The first two episodes collectively altered the upper-level flow pattern and markedly enhanced low-level winds throughout the warm sector. These modifications served as upscale feedbacks that contributed to the first episode’s exceptional severity and to the remarkable vertical shear profiles that supported numerous long-track and violent tornadoes during the final episode on the afternoon of 27 April.

Multiscale Aspects of the 26–27 April 2011 Tornado Outbreak. Part I: Outbreak Chronology and Environmental Evolution

Abstract One of the most prolific tornado outbreaks ever documented occurred on 26–27 April 2011 and comprised three successive episodes of tornadic convection that primarily impacted the southeastern United States, including two quasi-linear convective systems (hereinafter QLCS1 and QLCS2) that preceded the notorious outbreak of long-track, violent tornadoes spawned by numerous supercells on the afternoon of 27 April. The ∼36-h period encompassing these three episodes was part of a longer multiday outbreak that occurred ahead of a slowly moving upper-level trough over the Rocky Mountains. Here in Part I, we detail how the environment evolved to support this extended outbreak, with particular attention given to the three successive systems that each exhibited a different morphology and severity. The amplifying upper-level trough and attendant jet streak resulted from a Rossby wave–breaking event that yielded a complex tropopause structure and supported three prominent shortwave troughs that sequentially moved into the south-central United States. QLCS1 formed ahead of the second shortwave and was accompanied by rapid flow modifications, including considerable low-level jet (LLJ) intensification. The third shortwave moved into the lee of the Rockies early on 27 April to yield destabilization behind QLCS1 and support the formation of QLCS2, which was followed by further LLJ intensification and helped to establish favorable deep-layer shear profiles over the warm sector. The afternoon supercell outbreak commenced following the movement of this shortwave into the Mississippi Valley, which was attended by a deep tropopause fold, cold front aloft, and dryline that promoted two prominent bands of tornadic supercells over the Southeast. Significance Statement The tornado outbreak that impacted the United States on 26–27 April 2011 was part of an extended outbreak that produced 343 tornadoes and numerous fatalities. This paper is Part I of a study that describes the meteorological factors supporting such a prolific event. We focus on a 36-h period encompassing three convective episodes that impacted the Southeast and culminated in the widespread formation of long-track, violent tornadoes. Flow enhancements accompanying the first two episodes and the movement of a cold front aloft into the Southeast were found to contribute to the evolution of the final and most devastating episode. Part II describes how the first two episodes directly modified the environment to enhance the severity of this outbreak.

A Numerical Simulation of the “1907” Kaiyuan Tornado Weather Process in Liaoning, Northeast China

From 17:00 to 18:00 local standard time (LST) on 3 July 2019, a rare strong tornado occurred in Kaiyuan, Liaoning Province, northeast China. NCEP/NCAR 0.25° × 0.25° reanalysis data and WRF4.0 numerical prediction models were used to carry out the numerical simulation. Double nesting was adopted, and the horizontal grid distance was 9 km by 3 km. Based on the observation data of China meteorological observation stations, surface and upper charts, Doppler radar data, Himawari(HMW)-8 satellite images and numerical simulation results, the mesoscale structure and mechanism of the tornado were studied. The results show that: (1) At the northwest edge of the subtropical high, and the northeast cold vortex located in Northeast China, when the transverse trough moves southward, cold air is supplied continuously. Under the joint influence of the surface northeast cyclone, these are the main synoptic features of the tornado; (2) The northeast cold vortex cloud system was located at the junction of Heilongjiang and Jilin Provinces, and a squall line cloud system is formed. The tornado occurred at the tail of the squall line, and the strongest echo reached 65 dBZ. A mesocyclone, a 20 km northwest–southeast convergence belt, V-shaped gap, echo overhang structure and tornado vortex feature (TVS) were detected by the Doppler radar; (3) Before the tornado occurred, dry and cold air intruded from the northwest of the cold vortex, and a water vapor convergence zone appeared south of the squall line. The water vapor saturation zone with 80% relative humidity in northeast China was concentrated at 700 hPa, and the 20% dry column dropped down to 500 hPa between 115 and 124° E from the west. On the 850 hPa physical fields, there was a −20 × 10−5 s−1 convergence zone, and a 16 × 10−5 s−1 divergence belt appeared south and north of the squall line. A negative vorticity belt and a positive vorticity belt appeared south and north of the squall line, respectively. Kaiyuan is located at the smallest vertical shear, which is the junction place of three large vertical shear belts; (4) After 10:00 LST, the westerly wind 20 (10) m·s−1 dropped to 400 (800) hPa between 126 and 127° E. The northerly gale at 300 hPa north of 45° N moved southward. The rising center of the low level at 17:00 LST at approximately 45° N moved southward, and a sinking center appeared above it; (5) Several pairs of positive and negative vorticity columns formed between the lower troposphere and the place where the tornado occurred. There was convective instability at the lower level. CAPE increased, 0–3 km vertical wind shear increased, and LCL decreased remarkably during the afternoon.

Land Surface Effects on Shear Balance of Squall Lines

AbstractWe explore whether and how the land characteristics, especially surface drag, affect the squall line, in an idealized modeling framework. We find that the balance between the ambient low‐level shear and cold‐pool‐induced shear in the squall line can be modified by surface drag: it not only changes the ambient shear if near‐surface environmental wind is nonzero, but also reduces the cold‐pool‐induced shear by both weakening the low‐level wind and deepening the cold pool. The land surface impact on squall lines is larger with lower convective available potential energy (CAPE), partly because of stronger convection with higher CAPE. The cold pool intensity (vertically integrated negative buoyancy) could not explain the reduced cold pool shear induced by the land. Furthermore, land characteristics—such as roughness lengths—help maintain the shear balance and potentially make the squall line long‐lived, suggesting that they be included in convective (or cold pool) parameterizations to improve climate and Earth system models.

Climatological Features of Squall Line at the Borneo Coastline during Southwest Monsoon

Borneo Squall Line (BSL) is a disaster risk associated with intense rain and wind gust that affect the activities and residence near the northern coast of Borneo. Using 3-hourly rainfall from Tropical Rainfall Measuring Mission (TRMM) 3B42V7 during southwest monsoon season (May–September) from 1998–2018, a total of 629 squall days were identified. Their monthly and annual average was 6 and 30 days, respectively, with July representing the month with the highest number of squall line days. BSL is frequently initiated during midnight/predawn and terminated in the morning. Composite analyses of BSL days using the daily winds from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim revealed that lower tropospheric wind convergence is a crucial controlling factor for BSL formation. The position of the monsoon trough closer to the equatorial South China Sea (SCS), and strong westerly and south-westerly winds played an important role in creating this wind convergence region. Analyses of tropical cyclone (TC) data from the Regional Specialized Meteorological Centre (RSMC), Tokyo showed that nearly 72% of BSL occurred with the presence of TC. Spectral analysis exhibited prominent frequencies mainly in the 3–4- and 6-year time scale, which likely reflected the influence of interannual modulation of El-Niño Southern Oscillation (ENSO). Correlation coefficient between squall days and Sea Surface Temperature (SST) anomalies indicated that BSL increased after La-Niña events. This study is expected to have implications for real-time squall line forecasting in Malaysia and contributes toward a better understanding of BSL.

Tornadogenesis in a Quasi-Linear Convective System over Kanto Plain in Japan: A Numerical Case Study

Abstract The environmental characteristics and formation process of a tornado spawned by a quasi-linear convective system (QLCS) over Kanto Plain, Japan, are examined using observations, a reanalysis dataset, and a high-resolution numerical simulation with a horizontal grid spacing of 50 m. The QLCS environment responsible for tornadogenesis was characterized by small convective available potential energy and large storm-relative environmental helicity due to strong vertical shear associated with a low-level jet. The strong low-level jet was associated with a large zonal pressure gradient between two meridionally aligned extratropical cyclones and a synoptic-scale high pressure system to the east. The numerical simulation reproduced the tornado in the central part of the QLCS. Before the tornadogenesis, three mesovortices developed that were meridionally aligned at 500-m height, and a rear inflow jet (RIJ) associated with relatively cold air originated from aloft and developed on the west side of the QLCS, while descending from rear to front. Tornadogenesis occurred in the southernmost mesovortex at the northern tip of the RIJ. This mesovortex induces strong low-level updrafts through vertical pressure gradient force. A circulation analysis and vorticity budget analysis for the mesovortex show that environmental crosswise vorticity in the forward inflow region east of the QLCS played a significant role in the formation of the mesovortex. The circulation analysis for the tornado shows that frictional effects contribute to the increase of circulation associated with the tornado. Moreover, environmental shear associated with horizontal and vertical shear of the horizontal wind also contribute to the circulation of the tornado.

Biases in the Prediction of Convective Storm Characteristics with a Convection Allowing Ensemble

Abstract The severity, duration, and spatial extent of thunderstorm impacts are related to convective storm mode. This study assesses the skill of the High-Resolution Rapid Refresh Ensemble (HRRR-E) and its deterministic counterpart (HRRRv4) at predicting convective mode and storm macrophysical properties using 35 convective events observed during the 2020 warm season across the eastern United States. Seven cases were selected from each of five subjectively determined convective organization modes: tropical cyclones, mesoscale convective systems (MCSs), quasi-linear convective systems, clusters, and cellular convection. These storm events were assessed using an object-based approach to identify convective storms and determine their individual size. Averaged across all 35 cases, both the HRRR-E and HRRRv4 predicted storm areas were generally larger than observed, with this bias being a function of storm lifetime and convective mode. Both modeling systems also underpredicted the rapid increase in storm counts during the initiation period, particularly for the smaller-scale storm modes. Interestingly, performance of the HRRRv4 differed from that of the HRRR-E, with the HRRRv4 generally having a larger bias in total storm area than the HRRR-E due to HRRRv4 predicting up to 66% more storm objects than the HRRR-E. The HRRR-E accurately predicted the convective mode 65% of the time, with complete misses being very rare (<5% of the time overall). However, an evaluation of rank histograms across all 35 cases revealed that the HRRR-E tended to be underdispersive when predicting storm size for all but the MCS mode.