The Early Evening Transition in Southeastern US Tornado Environments

2021 ◽  
Author(s):  
Matthew C. Brown ◽  
Christopher J. Nowotarski ◽  
Andrew R. Dean ◽  
Bryan T. Smith ◽  
Richard L. Thompson ◽  
...  
Keyword(s):  
Precipitable Water ◽  
Convective System ◽  
High Shear ◽  
Evening Transition ◽  
Southeastern Us ◽  
Early Evening ◽  
Environmental Interactions ◽  
Southeast Us ◽  
Early Evening Transition ◽  
Forecast Guidance

AbstractThe response of severe local storms to environmental evolution across the early evening transition (EET) remains a forecasting challenge, particularly within the context of the Southeast US storm climatology, which includes the increased presence of low-CAPE environments and tornadic non-supercell modes. To disentangle these complex environmental interactions, Southeast severe convective reports spanning 2003-2018 are temporally binned relative to local sunset. Sounding-derived data corresponding to each report are used to characterize how the near-storm environment evolves across the EET, and whether these changes influence the mode, frequency, and tornadic likelihood of their associated storms. High-shear, high-CAPE (HSHC) environments are contrasted with high-shear, low-CAPE (HSLC) environments to highlight physical processes governing storm maintenance and tornadogenesis in the absence of large instability. Lastly, statistical analysis is performed to determine which aspects of the near-storm environment most effectively discriminate between tornadic (or significantly tornadic) and nontornadic storms towards constructing new sounding-derived forecast guidance parameters for multiple modal and environmental combinations. Results indicate that HSLC environments evolve differently than HSHC environments, particularly for non-supercell (e.g., quasi-linear convective system) modes. These low-CAPE environments sustain higher values of low-level shear and storm-relative helicity (SRH) and destabilize post-sunset – potentially compensating for minimal buoyancy. Furthermore, the existence of HSLC storm environments pre-sunset increases the likelihood of non-supercellular tornadoes post-sunset. Existing forecast guidance metrics such as the significant tornado parameter (STP) remain the most skillful predictors of HSHC tornadoes. However, HSLC tornado prediction can be improved by considering variables like precipitable water, downdraft CAPE, and effective inflow base.

scholarly journals Impacts of Increasing Low-Level Shear on Supercells during the Early Evening Transition*

2015 ◽  
Vol 143 (5) ◽  
pp. 1945-1969 ◽  
Author(s):  
Brice E. Coffer ◽  
Matthew D. Parker
Keyword(s):  
Wind Shear ◽  
Dynamic Pressure ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Dynamical Response ◽  
Vertical Vorticity ◽  
Low Level ◽  
Evening Transition ◽  
Early Evening ◽  
Early Evening Transition

Abstract The dynamical response of simulated supercells to temporally increasing lower-tropospheric vertical wind shear is investigated using idealized simulations. These simulations are based upon observed soundings from two cases that underwent an early evening transition during the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2). Mature supercells were simulated in observed afternoon environments with moderate vertical wind shear and then compared to simulated supercells experiencing observed evening increases in lower-tropospheric shear. The primary effect of the increase in low-level shear is to establish larger values of vertical vorticity at lower altitudes in the storm’s updraft. In turn, this leads to a nonlinear increase in the updraft strength due to the enhanced dynamic pressure minimum associated with larger vorticity in the storm’s mesocyclone. This is particularly important at low levels, where it increases the storm's ability to lift cool surface air (including outflow). Trajectories launched in developing vortices show that, despite comparable buoyant accelerations, parcels experience greater vertical velocity and stretching of vertical vorticity due to increased dynamic accelerations when the low-level shear is increased. Thus, even as low-level stability gradually increases in the early evening, the supercells’ low-level updraft intensity and surface vorticity production can increase. These results are consistent with climatological observations of a supercell’s likelihood of tornadogenesis during the early evening hours.

scholarly journals Comparison of Tropical Thunderstorm Estimation between Multiple Linear Regression, Dvorak, and ANFIS

2017 ◽  
Vol 6 (2) ◽  
pp. 149-158 ◽  
Author(s):  
Wayan Suparta ◽  
Wahyu Sasongko Putro
Keyword(s):  
Linear Regression ◽  
Multiple Linear Regression ◽  
Fuzzy Inference System ◽  
Fuzzy Inference ◽  
Meteorological Data ◽  
Precipitable Water ◽  
Thunderstorm Activity ◽  
Convective System ◽  
Inference System ◽  
Jacobi Algorithm

Thunderstorms are dangerous and it has increased due to highly precipitation and cloud cover density in the Mesoscale Convective System area. Climate change is one of the causes to increasing the thunderstorm activity. The present studies aimed to estimate the thunderstorm activity at the Tawau area of Sabah, Malaysia based on the Multiple Linear Regression (MLR), Dvorak technique, and Adaptive Neuro-Fuzzy Inference System (ANFIS). A combination of up to six inputs of meteorological data such as Pressure (P), Temperature (T), Relative Humidity (H), Cloud (C), Precipitable Water Vapor (PWV), and Precipitation (Pr) on a daily basis in 2012 were examined in the training process to find the best configuration system. By using Jacobi algorithm, H and PWV were identified to be correlated well with thunderstorms. Based on the two inputs that have been identified, the Sugeno method was applied to develop a Fuzzy Inference System. The model demonstrated that the thunderstorm activities during intermonsoon are detected higher than the other seasons. This model is comparable to the thunderstorm data that was collected manually with percent error below 50%.

scholarly journals A mesoscale convective system trapped along the Spanish Mediterranean Coast

2006 ◽  
Vol 7 ◽  
pp. 153-156 ◽  
Author(s):  
J. M. Sánchez-Laulhé
Keyword(s):  
Convective Instability ◽  
Heavy Rainfall ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Precipitable Water ◽  
Mediterranean Coast ◽  
Convective System ◽  
Convective Storm ◽  
Low Level ◽  
Mesoscale Convective

Abstract. This paper describes the evolution of a mesoscale convective system (MCS) developed over the Alboran Sea on 7 February 2005, using surface, upper-air stations, radar and satellite observations, and also data from an operational numerical model. The system developed during the night as a small convective storm line in an environment with slight convective instability, low precipitable water and strong low-level vertical wind shear near coast. The linear MCS moved northwards reaching the Spanish coast. Then it remained trapped along the coast for more than twelve hours, following the coast more than five hundred kilometres. The MCS here described had a fundamental orographic character due to: (1) the generation of a low-level storm inflow parallel to the coast, formed by blocking of the onshore flow by coastal mountains and (2) the orientation of both the mesoscale ascent from the sea towards the coastal mountains and the midlevel rear inflow from the coastal mountains to the sea. The main motivation of this work was to obtain a better understanding of the mechanisms relevant to the formation of heavy rainfall episodes occurring at Spanish Mediterranean coast associated with this kind of stationary or slowly moving MCSs.

scholarly journals The Development of Severe Vortices within Simulated High-Shear, Low-CAPE Convection

2019 ◽  
Vol 147 (6) ◽  
pp. 2189-2216 ◽  
Author(s):  
Keith D. Sherburn ◽  
Matthew D. Parker
Keyword(s):  
Wind Shear ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Convective System ◽  
High Shear ◽  
Low Level ◽  
Factor Ii ◽  
Strong Surface ◽  
Perturbation Pressure ◽  
Lapse Rates

Abstract Environments characterized by large values of vertical wind shear and modest convective available potential energy (CAPE) are colloquially referred to as high-shear, low-CAPE (HSLC) environments. Convection within these environments represents a considerable operational forecasting challenge. Generally, it has been determined that large low-level wind shear and steep low-level lapse rates—along with synoptic-scale forcing for ascent—are common ingredients supporting severe HSLC convection. This work studies the specific processes that lead to the development of strong surface vortices in HSLC convection, particularly associated with supercells embedded within a quasi-linear convective system (QLCS), and how these processes are affected by varying low-level shear vector magnitudes and lapse rates. Analysis of a control simulation, conducted with a base state similar to a typical HSLC severe environment, reveals that the key factors in the development of a strong surface vortex in HSLC embedded supercells are (i) a strong low- to midlevel mesocyclone, and (ii) a subsequent strong low-level updraft that results from the intense, upward-pointing dynamic perturbation pressure gradient acceleration. Through a matrix of high-resolution, idealized simulations, it is determined that sufficient low-level shear vector magnitudes are necessary for the development of low- to midlevel vertical vorticity [factor (i)], while steeper low-level lapse rates provide stronger initial low-level updrafts [factor (ii)]. This work shows why increased low-level lapse rates and low-level shear vector magnitudes are important to HSLC convection on the storm scale, while also revealing similarities between surface vortexgenesis in HSLC embedded supercells and higher-CAPE supercells.

scholarly journals Splitting of the middle layer of LPW SAFNWC/MSG satellite product in order to improve the monitoring of pre-convective environments

2008 ◽  
Vol 2 (1) ◽  
pp. 71-75
Author(s):  
G. Cuevas ◽  
M. A. Martinez ◽  
M. Velazquez ◽  
J. Ruiz ◽  
M. Manso
Keyword(s):  
Neural Networks ◽  
Precipitable Water ◽  
Middle Layer ◽  
Horizontal Resolution ◽  
Severe Weather ◽  
Convective System ◽  
Weather Event ◽  
Radar Images ◽  
The Impact ◽  
Severe Weather Event

Abstract. Seven of the infrared channels from the Spinning Enhanced Visible and Infrared Imagery (SEVIRI) instrument, on board the Meteosat Second Generation (MSG), are used to retrieve Layer Precipitable Water (LPW) and Stability Analysis Imagery (SAI) in the SAFNWC framework. Both products are retrieved using a statistical retrieval based on neural networks; they are routinely generated every fifteen minutes at a satellite horizontal resolution of 3 km in NADIR only in cloud-free areas. Many factors are involved in the development of severe weather and these parameters are only some of the indicators. However, due to the high resolution of these products, the use of them in conjunction with satellite and radar images can help to identify mesoscale features related to convection. The MSG moisture and parcel instability time trend fields are especially useful during the period previous to convection. Once the outbreak of convection occurs, the products calculated in the clear air pixels surrounding the convective system can give us hints to anticipate its evolution. SAFNWC LPW and SAI were analyzed for a severe weather event during August 2004. A thunderstorm over Teruel (Spain) produced intense precipitation and hail; a tornado developed while this thunderstorm was moving towards SE. The pre-convective parcel potential buoyancy and moisture SAFNWC products changed in a way that was consistent with the observed intense convective activity. In previous studies, the atmospheric moisture in medium levels, which has been proven to be relevant in some cases, was represented by only one level parameter (ML: middle layer LPW). However, it was observed that this layer is too thick to do an adequate analysis of moisture available for convection. Hence, an improvement on the LPW algorithm has been carried out by splitting the middle layer into two new sub-layers (approximately separated at 700 hPa) and training two new neural networks. The impact of monitoring moisture in the new sub-layers separately in this severe weather event has been tested, and the improvements achieved have been evaluated.

scholarly journals Cloud-resolving simulations of mercury scavenging and deposition in thunderstorms

2013 ◽  
Vol 13 (19) ◽  
pp. 10143-10157 ◽  
Author(s):  
U. S. Nair ◽  
Y. Wu ◽  
C. D. Holmes ◽  
A. Ter Schure ◽  
G. Kallos ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Convective Available Potential Energy ◽  
Precipitable Water ◽  
Atmospheric Modeling ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Rain Event ◽  
Lower Shear ◽  
Southeast Us ◽  
Northeast Us

Abstract. This study examines dynamical and microphysical features of convective clouds that affect mercury (Hg) wet scavenging and concentrations in rainfall. Using idealized numerical model simulations in the Regional Atmospheric Modeling System (RAMS), we diagnose vertical transport and scavenging of soluble Hg species – gaseous oxidized mercury (GOM) and particle-bound mercury (HgP), collectively Hg(II) – in thunderstorms under typical environmental conditions found in the Northeast and Southeast United States (US). Mercury scavenging efficiencies from various initial altitudes are diagnosed for a case study of a typical strong convective storm in the Southeast US. Assuming that soluble mercury concentrations are initially vertically uniform, the model results suggest that 60% of mercury deposited to the surface in rainwater originates from above the boundary layer (> 2 km). The free troposphere could supply a larger fraction of mercury wet deposition if GOM and HgP concentrations increase with altitude. We use radiosonde observations in the Northeast and Southeast to characterize three important environmental characteristics that influence thunderstorm morphology: convective available potential energy (CAPE), vertical shear (0–6 km) of horizontal wind (SHEAR) and precipitable water (PW). The Southeast US generally has lower SHEAR and higher CAPE and PW. We then use RAMS to test how PW and SHEAR impact mercury scavenging and deposition, while keeping the initial Hg(II) concentrations fixed in all experiments. We found that the mercury concentration in rainfall is sensitive to SHEAR with the nature of sensitivity differing depending upon the PW. Since CAPE and PW cannot be perturbed independently, we test their combined influence using an ensemble of thunderstorm simulations initialized with environmental conditions for the Northeast and Southeast US. These simulations, which begin with identical Hg(II) concentrations, predict higher mercury concentrations in rainfall from thunderstorms forming in the environmental conditions over the Southeast US compared to the Northeast US. A final simulation of a stratiform rain event produces lower mercury concentrations than in thunderstorms forming in environments typical of the Southeast US. The stratiform cloud scavenges mercury from the lowest ~ 4 km of the atmosphere, while thunderstorms scavenge up to ~ 10 km.

scholarly journals Atmospheric amines and ammonia measured with a Chemical Ionization Mass Spectrometer (CIMS)

2014 ◽  
Vol 14 (11) ◽  
pp. 16411-16450 ◽  
Author(s):  
Y. You ◽  
V. P. Kanawade ◽  
J. A. de Gouw ◽  
A. B. Guenther ◽  
S. Madronich ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Biomass Burning ◽  
Chemical Ionization ◽  
Fast Response ◽  
Daily Basis ◽  
Anthropogenic Sources ◽  
Ionization Mass ◽  
Southeastern Us ◽  
Temperature Dependences ◽  
Southeast Us

Abstract. We report ambient measurements of amines and ammonia with a~fast response chemical ionization mass spectrometer (CIMS) in a southeastern US forest in Alabama and a~moderately polluted Midwestern site during the summer. In the Alabama forest, mostly C3-amines (from pptv to tens of pptv) and ammonia (up to 2 ppbv) were detected on a daily basis. C3-amines and ammonia showed similar diurnal trends and temperature and wind direction dependences, and were not associated with transported CO and SO2 plumes. Consistent with temperature dependences, amine and ammonia in the gas and aerosol phases showed opposite diurnal trends, indicating gas-to-particle partitioning of amines and ammonia. Temperature dependences also imply reversible processes of amines and ammonia evaporation from soil surfaces in daytime and deposition of amines and ammonia to soil surfaces at nighttime. Various amines (C1–C6) at the pptv level were observed in the transported biomass burning plumes, showing that biomass burning can be a substantial source of amines in the Southeast US. At the moderately polluted Kent site, higher concentrations of amines (C1–C6, from pptv to tens of pptv) and ammonia (up to 6 ppbv) were detected. Diurnal variations of C1- to C3-amines and ammonia were correlated with the ambient temperature. C4- to C6-amines showed abrupt increases during the nighttime, suggesting that they were emitted from local sources. These abundant amines and ammonia may in part explain the frequent new particle formation events reported from Kent. Lower amine concentrations at the rural forested site highlight the importance of constraining anthropogenic sources of amines.

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