Abstract Observed supercell updrafts consistently produce the fastest mid- to upper-tropospheric vertical velocities among all modes of convection. Two hypotheses for this feature are investigated. In dynamic hypothesis, upward, largely rotationally driven pressure gradient accelerations enhance relative other forms thermodynamic have more low-level inflow than ordinary because large wind shear in environments. This makes wider that convection and less susceptible deleterious effects...

Abstract This paper uses idealized numerical simulations to investigate the dynamical influences of stable boundary layers on morphology supercell thunderstorms, especially development low-level rotation. Simulations are initialized in a horizontally homogeneous environment with surface-based layer similar that found within nocturnal or mesoscale cold pool. The depth and lapse rate imposed layer, which together control convective inhibition (CIN), varied suite experiments. When compared...

Abstract The self-organizing map (SOM) statistical technique is applied to vertical profiles of thermodynamic and kinematic parameters from a Rapid Update Cycle-2 (RUC-2) proximity sounding dataset with the goal better distinguishing predicting supercell tornadic environments. An SOM topologically ordered mapping input data onto two-dimensional array nodes that can be used classify large datasets into meaningful clusters. relative ability SOMs derived each parameter separate soundings in way...

Abstract The relationship between storm-relative helicity (SRH) and streamwise vorticity ωs is frequently invoked to explain the often robust connections effective inflow layer (EIL) SRH various supercell updraft properties. However, definition of also contains (SR) flow, separate influences SR flow on dynamics are therefore convolved when used as a diagnostic tool. To clarify this issue, proximity soundings numerical experiments disentangle EIL characteristics. Our results suggest that...

Long-lived supercells and tornadoes often persist into the night present a significant risk to society. While there is some understanding of initiation maintenance these storms during day, less known about how they evolve through environmental changes early evening transition (EET). This study compares near-storm environments different supercell evolution types tornadic vs non-tornadic in Southern Plains using parameters derived from Rapid Refresh (RAP) model analysis gridpoint soundings....

Accurately distinguishing and warning convective cells in the outer rainbands of landfalling tropical cyclones (TC) that will produce tornadoes (TCTORs) presents considerable challenges for forecasters. To enhance efforts, this study compares near-cell environments between tornadic (including both hits misses) warned nontornadic (false alarms) contiguous United States from 2013 to 2020. For each cell, RAP analysis gridpoint proximity soundings were obtained represent environment compared...

Abstract This paper reports on results of idealized numerical simulations testing the influence low-level humidity, and thus lifting condensation level (LCL), morphology evolution rotation in supercell thunderstorms. Previous studies have shown that LCL can outflow buoyancy, which turn affect generation stretching near-surface vertical vorticity. A less explored hypothesis is tested: affects relative positioning circulation overlying mesocyclone, influencing dynamic intensification To test...

Abstract This research investigates a hypothesis posed by previous authors, which argues that the helical nature of flow in supercell updrafts makes them more resistant to entrainment than nonsupercellular because suppressed turbulence purely flows. It was further supposed this resistance contributes steadiness and longevity updrafts. A series idealized large-eddy simulations were run address idea, wherein deep-layer shear hodograph shape varied, resulting supercells strongly sheared runs,...

Abstract In supercell environments, previous authors have shown strong connections between the vertical wind shear magnitude, updraft width, and entrainment. Based on these results, it is hypothesized that influences of entrainment-driven dilution buoyancy maximum velocity w in environments are a predictable function profile. It also pressure perturbation forces small because nearly complete offset upward dynamic downward buoyant forces. To address hypotheses, we derive formula for...

Abstract This study investigates relationships between climate-scale patterns and seasonal tornado outbreaks across the southeastern United States. Time series of several daily climate indices—including Arctic Oscillation (AO), North Atlantic (NAO), Pacific–North American (PNA) pattern, east/west Pacific (EPO/WPO), both raw detrended Gulf Mexico SST anomalies (SSTA/SSTAD)—are collected in advance Southeast severe convective days grouped using self-organizing maps (SOMs). Spatiotemporal...

Abstract Simulations of supercell thunderstorms in a sheared convective boundary layer (CBL), characterized by quasi-two-dimensional rolls, are compared with simulations having horizontally homogeneous environments. The effects convection on the general characteristics and low-level mesocyclones simulated supercells investigated for rolls oriented either perpendicular or parallel to storm motion, as well without cloud shading. Bulk measures strength not greatly affected presence near-storm...

Abstract This study investigates the changes that simulated supercell thunderstorms impart on their surroundings. Supercells are in a strongly sheared convective boundary layer comprising horizontal roll vortices. In sensitivity tests, effects of cloud shading near-storm environment explored through removal ice, water, and hydrometeor parameterized radiation. All supercells increase low-level shear proximal environment; however, this effect is more pronounced when included. Shading...

Abstract Supercell thunderstorms are simulated using an idealized numerical model to analyze the effects of modifications environmental low-level wind profile on near-surface rotation. Specifically, orientation, magnitude, and depth vertical shear modified in several suites experiments compared control simulations with no prescribed layer. The overall morphology supercells is highly sensitive even shallow changes profile. Moreover, maximum vorticity varies as modified. results suggest this...

Abstract Permafrost is an important indicator of climate change that affects, e.g., ecosystems, hydrology, and infrastructure in cold regions. Interactions between the surface atmosphere permafrost regions are complex vary seasonally due to contrasting energy moisture conditions frozen versus unfrozen ground. Differences surface‐atmosphere connections have been documented types, with significantly increased feedbacks areas continuous Eurasian permafrost, but no such relationship other This...

Abstract This article introduces a novel hypothesis for the role of vertical wind shear (“shear”) in deep convection initiation (DCI). In this hypothesis, initial moist updrafts that exceed width and threshold will “root” within progressively deeper steering current with time, increase their low-level cloud-relative flow inflow, widen, subsequently reduce susceptibility to entrainment-driven dilution, evolving toward quasi-steady self-sustaining state. contrast, do not aforementioned...

Abstract Nearly all previous numerical simulations of supercell thunderstorms have neglected surface fluxes heat, moisture, and momentum. This choice precludes horizontal inhomogeneities associated with dry boundary layer convection in the near-storm environment. As part a broader study on how mature are affected by convective (CBL) quasi-two-dimensional features (i.e., rolls), this paper documents methods used to develop realistic CBL an idealized environment supportive supercells. The...

Abstract Self-organizing maps (SOMs) have been shown to be a useful tool in classifying meteorological data. This paper builds on earlier work employing SOMs classify model analysis proximity soundings from the near-storm environments of tornadic and nontornadic supercell thunderstorms. A series multivariate is produced wherein input variables, height, dimensions, number SOM nodes are varied. including information regarding wind profile more effective discriminating between storms than those...

Abstract Proper prediction of the inflow layer deep convective storms is critical for understanding their potential updraft properties and likelihood producing severe weather. In this study, an existing forecast metric known as effective (EIL) evaluated with emphasis on its performance supercell thunderstorms, where both buoyancy dynamic pressure accelerations are common. A total 15 idealized simulations a range realistic base states performed. Using array passive fluid tracers initialized...

Abstract Tropical cyclone tornadoes pose a unique challenge to warning forecasters given their often marginal environments and radar attributes. In late August 2017 Hurricane Harvey made landfall on the Texas coast produced 52 over record-breaking seven consecutive days. To improve efforts, this case study of Harvey’s includes an event overview as well comparison near-cell attributes between tornadic nontornadic warned cells. Our results suggest that significant differences existed in both...

Abstract Vertical wind shear is known to affect supercell thunderstorms by displacing updraft hydrometeor mass downshear, thereby facilitating the storms’ longevity. Shear also impacts size of updrafts, with stronger leading wider, less dilute, and updrafts likely greater production. To more clearly define role across different vertical layers on concentrations displacements relative a suite idealized numerical model simulations supercells was conducted. magnitudes were systematically varied...

Abstract During the DOE Atmospheric Radiation Measurement (ARM) Tracking Aerosol Convection Interactions Experiment (TRACER) IOP spanning June–September 2022, two fixed ARM sites and a mobile team concurrently sampled airmass heterogeneity across sea- bay-breeze fronts around greater Houston metropolitan region. Here, we quantify spatiotemporal variability between maritime (coastal/bay side of breeze fronts) continental (inland air masses over 15 days characterized by strong sea-breeze...

Abstract Tropical cyclone tornadoes (TCTORs) are a hazard to life and property during landfalling tropical cyclones (TCs). The threat is often spread over wide area within the TC envelope must be continually evaluated as moves inland dissipates. To anticipate risk of TCTORs, forecasters may use high-resolution, rapidly updating model analyses short-range forecasts such Rapid Refresh (RAP) High-Resolution (HRRR), an ingredients-based approach similar that used for forecasting continental...

Abstract This study evaluates a hypothesis for the role of vertical wind shear in deep convection initiation (DCI) that was introduced Part I by examining behavior series numerical simulations. The states, “Initial moist updrafts exceed width and threshold will ‘root’ within progressively deeper steering current with time, increase their low-level cloud-relative flow inflow, widen, subsequently reduce susceptibility to entrainment-driven dilution, evolving toward quasi-steady self-sustaining...

In the winter and summer North Pacific Subtropical Countercurrent region, atmospheric responses to 20,000+ mesoscale oceanic eddies (MOEs) are examined using satellite reanalysis data from 1999 2013. The composite results indicate that surface wind speed, cloud, precipitation anomalies positively correlated with sea temperature in both seasons. speed convective show dipolar structures centering on MOEs unipolar summer. seasons, vertical mixing mechanism plays an obvious role MOEs. addition,...