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1. Introduction Squall-line maintenance and intensity have been studied for some time (e.g., Newton 1950 ), with an emerging understanding that the convective region of many squall lines occurs along the downshear edge of their outflow boundaries. Early numerical experiments (e.g., Hane 1973 ; Thorpe et al. 1982 ) helped to quantify the impacts of vertical wind shear upon such squall lines. Decades of observations and simulations were reviewed by Rotunno et al. (1988
1. Introduction Squall-line maintenance and intensity have been studied for some time (e.g., Newton 1950 ), with an emerging understanding that the convective region of many squall lines occurs along the downshear edge of their outflow boundaries. Early numerical experiments (e.g., Hane 1973 ; Thorpe et al. 1982 ) helped to quantify the impacts of vertical wind shear upon such squall lines. Decades of observations and simulations were reviewed by Rotunno et al. (1988
shear of a “representative” inflow sounding still largely determine the outcome? Does long-lived forcing matter once the convection has formed, with its attendant strong updrafts, downdrafts, and cold pool? This study addresses the role of persistent forcing in the early development and structure of deep convective squall lines. Two-dimensional forcing was selected for its relative simplicity (conceptually and through numerical simulation), here taken to be a cold front, formed and evolving as an
shear of a “representative” inflow sounding still largely determine the outcome? Does long-lived forcing matter once the convection has formed, with its attendant strong updrafts, downdrafts, and cold pool? This study addresses the role of persistent forcing in the early development and structure of deep convective squall lines. Two-dimensional forcing was selected for its relative simplicity (conceptually and through numerical simulation), here taken to be a cold front, formed and evolving as an
1. Introduction The north coast of South America is affected by mesoscale convective cloud clusters (CCCs) and their organization into squall lines (SL) parallel to the coast ( Garstang et al. 1994 ; Cohen et al. 1995 , 2009 ). These systems contribute nearly 40% of the annual precipitation of northern coastal Brazil and adjoining regions. Heavy afternoon showers caused by these systems disrupt the society in the coastal cities of Brazil ( Loureiro et al. 2014 ). Flash floods not only damage
1. Introduction The north coast of South America is affected by mesoscale convective cloud clusters (CCCs) and their organization into squall lines (SL) parallel to the coast ( Garstang et al. 1994 ; Cohen et al. 1995 , 2009 ). These systems contribute nearly 40% of the annual precipitation of northern coastal Brazil and adjoining regions. Heavy afternoon showers caused by these systems disrupt the society in the coastal cities of Brazil ( Loureiro et al. 2014 ). Flash floods not only damage
1. Introduction Squall lines are linear or quasi-linear mesoscale convective systems (MCSs) that can produce heavy rains, damaging winds, hail, and sometimes even tornadoes. A squall line is defined as “a line of active thunderstorms, either continuous or with breaks, including contiguous precipitation areas resulting from the existence of the thunderstorms ( Glickman 2000 ).” Common radar signatures of squall lines are composed of a leading edge of a convective rainband with a width of several
1. Introduction Squall lines are linear or quasi-linear mesoscale convective systems (MCSs) that can produce heavy rains, damaging winds, hail, and sometimes even tornadoes. A squall line is defined as “a line of active thunderstorms, either continuous or with breaks, including contiguous precipitation areas resulting from the existence of the thunderstorms ( Glickman 2000 ).” Common radar signatures of squall lines are composed of a leading edge of a convective rainband with a width of several
1. Introduction Tropical cyclones (TCs) can produce severe weather conditions not only within its circulation, but also in its ambient environment. Galarneau et al. (2010) analyzed predecessor rainfall events (PRE) appearing about 1000 km poleward of recurving TCs east of a midlatitude trough with the rich moisture supply provided by the landfalling TC. The intent of this study is to document the existence and nature of squall lines preceding landfalling TCs (pre-TC), which are linear
1. Introduction Tropical cyclones (TCs) can produce severe weather conditions not only within its circulation, but also in its ambient environment. Galarneau et al. (2010) analyzed predecessor rainfall events (PRE) appearing about 1000 km poleward of recurving TCs east of a midlatitude trough with the rich moisture supply provided by the landfalling TC. The intent of this study is to document the existence and nature of squall lines preceding landfalling TCs (pre-TC), which are linear
1. Introduction For common storms, such as squall lines, propagation is dependent on the precipitation. More precisely, some of the precipitation evaporates before reaching the surface, establishing a subcloud cold pool that spreads along the ground. This pool helps lift moist, low-level air into the storm at its leading edge or gust front. Even though this ascent tends to get temporally punctuated into individual convective cells, this mechanism can be termed continuous propagation, the
1. Introduction For common storms, such as squall lines, propagation is dependent on the precipitation. More precisely, some of the precipitation evaporates before reaching the surface, establishing a subcloud cold pool that spreads along the ground. This pool helps lift moist, low-level air into the storm at its leading edge or gust front. Even though this ascent tends to get temporally punctuated into individual convective cells, this mechanism can be termed continuous propagation, the
1. Introduction A squall line is a line of active thunderstorms, either continuous or with breaks, including contiguous precipitation areas resulting from the existence of the thunderstorms ( Glickman 2000 ). Many squall lines last for hours and are capable of producing a variety of damaging weather. Although only the strongest squall lines typically are associated with tornado activity, many produce high winds, hail, or other significant weather. Many observational studies have noted the
1. Introduction A squall line is a line of active thunderstorms, either continuous or with breaks, including contiguous precipitation areas resulting from the existence of the thunderstorms ( Glickman 2000 ). Many squall lines last for hours and are capable of producing a variety of damaging weather. Although only the strongest squall lines typically are associated with tornado activity, many produce high winds, hail, or other significant weather. Many observational studies have noted the
are known to encounter complex terrain (e.g., Chen and Chou 1993 ; Keighton et al. 2007 ). Explorations of topography and organized convection have increased in recent years, including both observationally based (e.g., Keighton et al. 2007 ; Parker and Ahijevych 2007 ) and modeling-based studies (e.g., Frame and Markowski 2006 , hereafter FM06 ; Reeves and Lin 2007 ). Letkewicz and Parker (2010 , hereafter LP10) built upon the work of Keighton et al. (2007) by examining 40 squall lines
are known to encounter complex terrain (e.g., Chen and Chou 1993 ; Keighton et al. 2007 ). Explorations of topography and organized convection have increased in recent years, including both observationally based (e.g., Keighton et al. 2007 ; Parker and Ahijevych 2007 ) and modeling-based studies (e.g., Frame and Markowski 2006 , hereafter FM06 ; Reeves and Lin 2007 ). Letkewicz and Parker (2010 , hereafter LP10) built upon the work of Keighton et al. (2007) by examining 40 squall lines
important source of coastal precipitation is seaward-propagating mesoscale convection system (MCS), or squall lines, which are modified by these coastal circulations ( Wu et al. 2009 ; Lombardo and Colle 2011 , 2012 , 2013 ; Li and Carbone 2015 ; Lombardo and Kading 2018 , hereafter LK18 ). Therefore, advancing our knowledge of the mechanisms responsible for coastal precipitation enhancements necessitates an understanding of deep convective storm dynamics over coastal environments. As deep
important source of coastal precipitation is seaward-propagating mesoscale convection system (MCS), or squall lines, which are modified by these coastal circulations ( Wu et al. 2009 ; Lombardo and Colle 2011 , 2012 , 2013 ; Li and Carbone 2015 ; Lombardo and Kading 2018 , hereafter LK18 ). Therefore, advancing our knowledge of the mechanisms responsible for coastal precipitation enhancements necessitates an understanding of deep convective storm dynamics over coastal environments. As deep
crossed northern Florida and dissipated over the Atlantic Ocean, 33 h after its formation. MCSs in the form of squall lines frequently occur in the Great Plains and central United States. Squall lines are most often observed immediately ahead of a cold front (CF), associated with a developing low pressure system. The initiation of deep convection results from convergence and subsequent ascent in the low levels of the atmosphere, typically within the atmospheric boundary layer (ABL). Numerous
crossed northern Florida and dissipated over the Atlantic Ocean, 33 h after its formation. MCSs in the form of squall lines frequently occur in the Great Plains and central United States. Squall lines are most often observed immediately ahead of a cold front (CF), associated with a developing low pressure system. The initiation of deep convection results from convergence and subsequent ascent in the low levels of the atmosphere, typically within the atmospheric boundary layer (ABL). Numerous
