Relationship of convection initiation and subsequent storm strength to ensemble simulated environmental conditions during IOP3b of VORTEX Southeast 2017

2021 ◽  
Author(s):  
STANLEY B. TRIER ◽  
GLEN S. ROMINE ◽  
DAVID A. AHIJEVYCH ◽  
RYAN A. SOBASH ◽  
MANDA B. CHASTEEN
Keyword(s):  
Cold Front ◽  
Convective Available Potential Energy ◽  
Mesoscale Convective System ◽  
Severe Weather ◽  
Convective System ◽  
Ensemble Mean ◽  
Adiabatic Cooling ◽  
Mesoscale Convective ◽  
Convection Initiation ◽  
Relationship Of

AbstractA fifty-member convection allowing ensemble was used to examine environmental factors influencing afternoon convection initiation (CI) and subsequent severe weather on 5 April 2017 during Intensive Observing Period (IOP) 3b of the Verification of Rotation in Tornadoes Experiment in the Southeast (VORTEX-SE). This case produced several weak tornadoes (rated EF1 or less), and numerous reports of significant hail (diameter ≥ 2 inches), ahead of an eastward-moving surface cold front over eastern Alabama and southern Tennessee. Both observed and simulated CI was facilitated by mesoscale lower-tropospheric ascent maximized several tens of km ahead of the cold-frontal position, and the simulated mesoscale ascent was linked to surface frontogenesis in the ensemble mean. Simulated maximum 2-5-km AGL updraft helicity (UHmax) was used as a proxy for severe-weather producing mesocyclones, and considerable variability in UHmax occurred among the ensemble members. Ensemble members with UHmax > 100 m2 s-2 had stronger mesoscale ascent than in members with UHmax < 75 m2 s-2, which facilitated more timely CI by producing greater adiabatic cooling and moisture increases above the PBL. After CI, storms in the larger UHmax members moved northeastward toward a mesoscale region with larger convective available potential energy (CAPE) than in smaller UHmax members. The CAPE differences among members was influenced by differences in location of an antecedent mesoscale convective system, which had a thermodynamically stabilizing influence on the environment toward which storms were moving. Despite providing good overall guidance, the model ensemble overpredicted severe weather likelihoods in northeastern Alabama, where comparisons with VORTEX-SE soundings revealed a positive CAPE bias.

scholarly journals The Mechanism and Predictability of an Elevated Convection Initiation Event in a Weak-Lifting Environment in Central-Eastern China

2019 ◽  
Vol 147 (5) ◽  
pp. 1823-1841 ◽  
Author(s):  
Murong Zhang ◽  
Zhiyong Meng ◽  
Yipeng Huang ◽  
Dongyong Wang
Keyword(s):  
Eastern China ◽  
Mesoscale Convective System ◽  
Early Morning ◽  
Lapse Rate ◽  
Convective System ◽  
Surface Front ◽  
Adiabatic Cooling ◽  
Mesoscale Convective ◽  
Central Eastern ◽  
Convection Initiation

Abstract An elevated convection initiation (CI) of a quasi-linear mesoscale convective system (MCS) that occurred in a weak-lifting environment in the early morning on 23 June 2016 in central-eastern China was investigated using observational analysis and convection-permitting numerical simulations. This MCS gradually developed into a surface-based MCS and eventually produced a strong supercell that spawned an EF4 tornado in Yancheng City of Jiangsu Province and killed 98 people. This elevated MCS was initiated ahead of a surface front without identifiable boundaries at the surface. An elevated moist absolutely unstable layer (MAUL) was found to be conducive to the CI. The MAUL provided negligible convective inhibition and contributed to CI without strong-lifting mechanisms. Numerical simulation results showed that the formation of the elevated MAUL was mainly attributed to adiabatic cooling by weak vertical ascent and sufficient horizontal moisture transport near the terminus of a low-level jet. The weak vertical ascent before the CI was sloping and was likely to be relevant to the layer-lifting process associated with the realization of potential instability. The results showed that the MAUL in this weak-lifting environment was characterized by a shallower depth, a weaker lapse rate, and a longer sustaining period than the conditions in a strong-lifting environment. The predictability of this elevated CI case was examined using a 10-member ensemble forecast. A total of 80% of the ensemble members captured the CI. Rather than a difference in lifting, whether having an elevated MAUL or not was the major difference between CI and non-CI members in the present case.

scholarly journals Derecho Evolving from a Mesocyclone—A Study of 11 August 2017 Severe Weather Outbreak in Poland: Event Analysis and High-Resolution Simulation

2019 ◽  
Vol 147 (6) ◽  
pp. 2283-2306 ◽  
Author(s):  
Mateusz Taszarek ◽  
Natalia Pilguj ◽  
Juliusz Orlikowski ◽  
Artur Surowiecki ◽  
Szymon Walczakiewicz ◽  
...  
Keyword(s):  
High Resolution ◽  
Initial Conditions ◽  
Convective Available Potential Energy ◽  
Severe Weather ◽  
Mature Stage ◽  
Convective System ◽  
Event Analysis ◽  
Atmospheric Conditions ◽  
Mesoscale Convective ◽  
Resolution Simulation

Abstract This study documents atmospheric conditions, development, and evolution of a severe weather outbreak that occurred on 11 August 2017 in Poland. The emphasis is on analyzing system morphology and highlighting the importance of a mesovortex in producing the most significant wind damages. A derecho-producing mesoscale convective system (MCS) had a remarkable intensity and was one of the most impactful convective storms in the history of Poland. It destroyed and partially damaged 79 700 ha of forest (9.8 million m3 of wood), 6 people lost their lives, and 58 were injured. The MCS developed in an environment of high 0–3-km wind shear (20–25 m s−1), strong 0–3-km storm relative helicity (200–600 m2 s−2), moderate most-unstable convective available potential energy (1000–2500 J kg−1), and high precipitable water (40–46 mm). Within the support of a midtropospheric jet, the MCS moved northeast with a simultaneous northeastward inflow of warm and very moist air, which contributed to strong downdrafts. A mesocyclone embedded in the convective line induced the rear inflow jet (RIJ) to descend and develop a bow echo. In the mature stage, a supercell evolved into a bookend vortex and later into a mesoscale convective vortex. Swaths of the most significant wind damage followed the aforementioned vortex features. A high-resolution simulation performed with initial conditions derived from GFS and ECMWF global models predicted the possibility of a linear MCS with widespread damaging wind gusts and embedded supercells. Simulations highlighted the importance of cloud cover in the preconvective environment, which influenced the placement and propagation of the resulting MCS.

scholarly journals The Impact of Low-Level Moisture Errors on Model Forecasts of an MCS Observed during PECAN

2017 ◽  
Vol 145 (9) ◽  
pp. 3599-3624 ◽  
Author(s):  
John M. Peters ◽  
Erik R. Nielsen ◽  
Matthew D. Parker ◽  
Stacey M. Hitchcock ◽  
Russ S. Schumacher
Keyword(s):  
Convective Available Potential Energy ◽  
Mesoscale Convective System ◽  
Squall Line ◽  
Convective System ◽  
Low Level ◽  
Eastern Flank ◽  
Western Flank ◽  
Mesoscale Convective ◽  
Outflow Boundary ◽  
The Impact

This article investigates errors in forecasts of the environment near an elevated mesoscale convective system (MCS) in Iowa on 24–25 June 2015 during the Plains Elevated Convection at Night (PECAN) field campaign. The eastern flank of this MCS produced an outflow boundary (OFB) and moved southeastward along this OFB as a squall line. The western flank of the MCS remained quasi stationary approximately 100 km north of the system’s OFB and produced localized flooding. A total of 16 radiosondes were launched near the MCS’s eastern flank and 4 were launched near the MCS’s western flank. Convective available potential energy (CAPE) increased and convective inhibition (CIN) decreased substantially in observations during the 4 h prior to the arrival of the squall line. In contrast, the model analyses and forecasts substantially underpredicted CAPE and overpredicted CIN owing to their underrepresentation of moisture. Numerical simulations that placed the MCS at varying distances too far to the northeast were analyzed. MCS displacement error was strongly correlated with models’ underrepresentation of low-level moisture and their associated overrepresentation of the vertical distance between a parcel’s initial height and its level of free convection ([Formula: see text], which is correlated with CIN). The overpredicted [Formula: see text] in models resulted in air parcels requiring unrealistically far northeastward travel in a region of gradual meso- α-scale lift before these parcels initiated convection. These results suggest that erroneous MCS predictions by NWP models may sometimes result from poorly analyzed low-level moisture fields.

scholarly journals Long-Lived Mesoscale Systems in a Low–Convective Inhibition Environment. Part II: Downshear Propagation

2015 ◽  
Vol 72 (11) ◽  
pp. 4319-4336 ◽  
Author(s):  
Mitchell W. Moncrieff ◽  
Todd P. Lane
Keyword(s):  
Convective Available Potential Energy ◽  
Mesoscale Convective System ◽  
Cold Pool ◽  
Convective System ◽  
Mesoscale Circulation ◽  
Secondary Importance ◽  
Convective Systems ◽  
Stratiform Region ◽  
Mesoscale System ◽  
Mesoscale Convective

Abstract Part II of this study of long-lived convective systems in a tropical environment focuses on forward-tilted, downshear-propagating systems that emerge spontaneously from idealized numerical simulations. These systems differ in important ways from the standard mesoscale convective system that is characterized by a rearward-tilted circulation with a trailing stratiform region, an overturning updraft, and a mesoscale downdraft. In contrast to this standard mesoscale system, the downshear-propagating system considered here does not feature a mesoscale downdraft and, although there is a cold pool it is of secondary importance to the propagation and maintenance of the system. The mesoscale downdraft is replaced by hydraulic-jump-like ascent beneath an elevated, forward-tilted overturning updraft with negligible convective available potential energy. Therefore, the mesoscale circulation is sustained almost entirely by the work done by the horizontal pressure gradient and the kinetic energy available from environmental shear. This category of organization is examined by cloud-system-resolving simulations and approximated by a nonlinear archetypal model of the quasi-steady Lagrangian-mean mesoscale circulation.

scholarly journals Serial Upstream-Propagating Mesoscale Convective System Events over Southeastern South America

2008 ◽  
Vol 136 (8) ◽  
pp. 3087-3105 ◽  
Author(s):  
Vagner Anabor ◽  
David J. Stensrud ◽  
Osvaldo L. L. de Moraes
Keyword(s):  
South America ◽  
Convective Available Potential Energy ◽  
Mesoscale Convective System ◽  
The United States ◽  
Convective System ◽  
Pressure System ◽  
Low Level ◽  
The North ◽  
Synoptic Conditions ◽  
Mesoscale Convective

Abstract Serial mesoscale convective system (MCS) events with lifetimes over 18 h and up to nearly 70 h are routinely observed over southeastern South America from infrared satellite imagery during the spring and summer. These events begin over the southern La Plata River basin, with individual convective systems generally moving eastward with the cloud-layer-mean wind. However, an important and common subset of these serial MCS events shows individual MCSs moving to the east or southeast, yet the region of convective development as a whole shifts upstream to the north or northwest. Analyses of the composite mean environments from 10 of these upstream-propagating serial MCS events using NCEP–NCAR reanalysis data events indicates that the synoptic conditions resemble those found in mesoscale convective complex environments over the United States. The serial MCS events form within an environment of strong low-level warm advection and strong moisture advection between the surface and 700 hPa from the Amazon region southward. One feature that appears to particularly influence the low-level flow pattern at early times is a strong surface anticyclone located just off the coast of Brazil. At upper levels, the MCSs develop on the anticyclonic side of the entrance region to an upper-level jet. Mean soundings show that the atmosphere is moist from the surface to near 500 hPa, with values of convective available potential energy above 1200 J kg−1 at the time of system initiation. System dissipation and continued upstream propagation to the north and northwest occurs in tandem with a surface high pressure system that crosses the Andes Mountains from the west.

scholarly journals A Case Study of the Interaction of a Mesoscale Gravity Wave with a Mesoscale Convective System

2014 ◽  
Vol 142 (4) ◽  
pp. 1403-1429 ◽  
Author(s):  
James H. Ruppert ◽  
Lance F. Bosart
Keyword(s):  
Solitary Wave ◽  
Gravity Wave ◽  
Surface Pressure ◽  
Cold Front ◽  
Mesoscale Convective System ◽  
High Amplitude ◽  
Squall Line ◽  
Convective System ◽  
Density Currents ◽  
Mesoscale Convective

Abstract This study documents the high-amplitude mesoscale gravity wave (MGW) event of 7 March 2008 in which two MGWs strongly impacted the sensible weather over a large portion of the Southeast United States. These MGWs exhibited starkly contrasting character despite propagating within similar environments. The primary (i.e., long lived) MGW was manifest by a solitary wave of depression associated with rapid sinking motion and adiabatic warming, while the secondary (short lived) MGW was manifest by a solitary wave of elevation (“MGWEL”), dominated by rising motion and moist adiabatic cooling. Genesis of the primary MGW occurred as a strong cold front arrived at the foot of Mexico’s high terrain and perturbed the appreciable overriding flow. The resulting gravity wave became ducted in the presence of a low-level frontal stable layer, and caused surface pressure falls up to ~4 hPa. The MGW later amplified as it became coupled with a stratiform precipitation system, which led to its evolution into an intense mesohigh–wake low couplet. This couplet propagated as a ducted MGW attached to a stratiform system for ~12 h thereafter, and induced rapid surface pressure falls of ≥10 hPa (including a fall of 6.7 hPa in 10 min), rapid wind vector changes (e.g., 17 m s−1 in 25 min), and high wind gusts (e.g., 20 m s−1) across several states. MGWEL appeared within the remnants of a squall line, and was manifest by a sharp pressure ridge of ~6 hPa with a narrow embedded rainband following the motion of a surface cold front. MGWEL bore resemblance to previously documented gravity waves formed by density currents propagating through stable environments.

Tornadoes in the New York Metropolitan Region: Climatology and Multiscale Analysis of Two Events

2012 ◽  
Vol 27 (6) ◽  
pp. 1326-1348 ◽  
Author(s):  
Brian A. Colle ◽  
Kelly A. Lombardo ◽  
Jeffrey S. Tongue ◽  
William Goodman ◽  
Nelson Vaz
Keyword(s):  
New York ◽  
Convective Available Potential Energy ◽  
Structural Evolution ◽  
Mesoscale Convective System ◽  
Early Morning ◽  
Metropolitan Region ◽  
Convective System ◽  
Low Level ◽  
Warm Advection ◽  
Mesoscale Convective

Abstract This paper describes the climatology of tornadoes around New York City (NYC) and Long Island (LI), New York, and the structural evolution of two tornadic events that affected NYC on 8 August 2007 and 16 September 2010. Nearly half (18 of 34 events from 1950 to 2010) of NYC–LI tornadoes developed between 0500 and 1300 EDT, and August is the peak tornado month as compared to July for most of the northeast United States. A spatial composite highlights the approaching midlevel trough, moderate most unstable convective available potential energy (MUCAPE), and frontogenesis along a low-level baroclinic zone. Shortly before the early morning tornadoes on 8 August 2007, a mesoscale convective system intensified in the lee of the Appalachians in a region of low-level frontogenesis and moderate MUCAPE (~1500 J kg−1). Warm advection at low levels and evaporative cooling within an elevated mixed layer (EML) ahead of the mesoscale convective system (MCS) helped steepen the low-level lapse rates. Meanwhile, a surface mesolow along a quasi-stationary frontal zone enhanced the warm advection and low-level shear. The late afternoon event on 16 September 2010 was characterized by a quasi-linear convective system (QLCS) that also featured an EML aloft, a surface mesolow just west of NYC, low-level frontogenesis, and a southerly low-level jet ahead of an approaching midlevel trough. The QLCS intensified approaching NYC and generated mesovortices as the QLCS bowed outward. These cases illustrate the benefit of high-density surface observations, terminal Doppler radars, and sounding profiles from commercial aircraft for nowcasting these events.

scholarly journals Nocturnal Convection Initiation during PECAN 2015

2019 ◽  
Vol 100 (11) ◽  
pp. 2223-2239 ◽  
Author(s):  
Tammy M. Weckwerth ◽  
John Hanesiak ◽  
James W. Wilson ◽  
Stanley B. Trier ◽  
Samuel K. Degelia ◽  
...  
Keyword(s):  
Great Plains ◽  
Current Knowledge ◽  
Wrf Model ◽  
Mesoscale Convective System ◽  
Convective System ◽  
University Of Oklahoma ◽  
Different Types ◽  
Mesoscale Convective ◽  
Convection Initiation ◽  
The University

AbstractNocturnal convection initiation (NCI) is more difficult to anticipate and forecast than daytime convection initiation (CI). A major component of the Plains Elevated Convection at Night (PECAN) field campaign in the U.S. Great Plains was to intensively sample NCI and its near environment. In this article, we summarize NCI types observed during PECAN: 1 June–16 July 2015. These NCI types, classified using PECAN radar composites, are associated with 1) frontal overrunning, 2) the low-level jet (LLJ), 3) a preexisting mesoscale convective system (MCS), 4) a bore or density current, and 5) a nocturnal atmosphere lacking a clearly observed forcing mechanism (pristine). An example and description of each of these different types of PECAN NCI events are presented. The University of Oklahoma real-time 4-km Weather Research and Forecasting (WRF) Model ensemble forecast runs illustrate that the above categories having larger-scale organization (e.g., NCI associated with frontal overrunning and NCI near a preexisting MCS) were better forecasted than pristine. Based on current knowledge and data from PECAN, conceptual models summarizing key environmental features are presented and physical processes underlying the development of each of these different types of NCI events are discussed.

Probing a post monsoon Mesoscale Convective System (MCS) and the generated Transient Luminous Events (TLEs) over Indian Region

2020 ◽  
Author(s):  
Sidha Sankalpa Moharana ◽  
Rajesh Singh
Keyword(s):  
Convective Available Potential Energy ◽  
Mesoscale Convective System ◽  
Lower Atmosphere ◽  
Space Environment ◽  
Mature Stage ◽  
Convective System ◽  
Lightning Flash ◽  
Monsoon Period ◽  
Post Monsoon ◽  
Mesoscale Convective

&lt;p&gt;A Mesoscale Convective System (MCS), consisting of three Super Cells&lt;br&gt;formed over South-east Indian, is assessed in detail with satellite and ground based&lt;br&gt;data-sets. The MCS under investigation generated a total of Ten (10) upward&lt;br&gt;electrical discharges (9 Sprites and 1 Gigantic Jet) commonly named as Transient&lt;br&gt;Luminous Events (TLEs). The TLEs were recorded from TLE observation station&lt;br&gt;located at Allahabad, India. The event occurred in the Post-Monsoon period of 2013&lt;br&gt;on October 7, during 15-23 UT hours. The MCS was spread over a region of 25000 sq.&lt;br&gt;Kilometers. A lowest cloud top temperature value of -84.7 0 C was observed in the&lt;br&gt;mature stage of the MCS, during 2130 UT hours, and the cloud top altitude was&lt;br&gt;reaching 17.6 km. The coldest cloud top region was covering an average area of&lt;br&gt;13000 sq. Km. The measured Convective Available Potential Energy (CAPE) value was&lt;br&gt;606.9 J/kg at 00 UT on 7 th October which dropped to 211 J/kg at 00 UT on 8 th&lt;br&gt;October. The mean lightning flash rate during the formation and maturity stages of&lt;br&gt;the MCS was around 46.03 min -1 . During the entire lifespan of the thunderstorm,&lt;br&gt;peak currents were found to be reaching &amp;#177;400 kA. Such high electric currents,&lt;br&gt;extreme cold temperature and towering altitudes of the convective complexes show&lt;br&gt;how much a MCS is dynamically active and the TLEs which it produced are known to&lt;br&gt;electrically connect the lower atmosphere to the upper space environment.&lt;/p&gt;

scholarly journals Use of the Parcel Buoyancy Minimum (Bmin) to Diagnose Simulated Thermodynamic Destabilization. Part II: Composite Analysis of Mature MCS Environments

2014 ◽  
Vol 142 (3) ◽  
pp. 967-990 ◽  
Author(s):  
Stanley B. Trier ◽  
Christopher A. Davis ◽  
David A. Ahijevych ◽  
Kevin W. Manning
Keyword(s):  
Convective Available Potential Energy ◽  
Warm Season ◽  
Vertical Motion ◽  
Leading Edge ◽  
Composite Analysis ◽  
Convective Systems ◽  
Central United States ◽  
Adiabatic Cooling ◽  
Mesoscale Convective ◽  
Convection Initiation

Abstract Herein, the parcel buoyancy minimum (Bmin) defined in Part I of this two-part paper is used to examine physical processes influencing thermodynamic destabilization in environments of mature simulated mesoscale convective systems (MCSs). These convection-permitting simulations consist of twelve 24-h forecasts during two 6-day periods characterized by two different commonly occurring warm-season weather regimes that support MCSs over the central United States. A composite analysis of 22 MCS environments is performed where cases are stratified into surface-based (SB), elevated squall (ES), and elevated nonsquall (ENS) categories. A gradual reduction of lower-tropospheric Bmin to values indicative of small convection inhibition, occurring over horizontal scales &gt;100 km from the MCS leading edge, is a common aspect of each category. These negative buoyancy decreases are most pronounced for the ES and ENS environments, in which convective available potential energy (CAPE) is greatest for air parcels originating above the surface. The implication is that the vertical structure of the mesoscale environment plays a key role in the evolution and sustenance of convection long after convection initiation and internal MCS circulations develop, particularly in elevated systems. Budgets of Bmin forcing are computed for the nocturnally maturing ES and ENS composites. Though warm advection occurs through the entire 1.5-km-deep layer comprising the vertical intersection of the largest environmental CAPE and smallest environmental Bmin magnitude, the net effect of terms involving vertical motion dominate the destabilization in both composites. These effects include humidity increases in air parcels due to vertical moisture advection and the adiabatic cooling of the environment above.

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