line line line thunderstorms form ahead cold early 20th century term synonym cold contains heavy precipitation hail frequent lightning strong straight line winds possibly tornadoes strong straight line winds occur line shape bow echo tornadoes occur waves line echo wave pattern low pressure areas present bow echoes develop summer season known fast large sections territory edge rain shield associated mature lines wake low present associated heat burst theory polar theory developed derived dense network observation sites scandinavia world war theory proposed main cyclone concentrated lines convergence ahead low trailing low trailing convergence zone referred line cold areas clouds rainfall appeared focused convergence zone concept frontal zones led concept air masses nature dimensional structure cyclone development upper air network 1940s life cycle organized areas thunderstorms activity reinforce pre existing frontal zones cold fronts occurs pattern upper level jet splits streams resultant convective system forms point upper level split wind pattern area best low level convection moves east equator warm sector parallel low level thickness lines convection strong linear curved called line feature placed leading edge significant wind shift pressure rise feature commonly depicted warm season united_states surface analyses lie sharp surface lines form arid regions known result high winds wake picking dust desert floor mature lines wake low develop edge rain shield lead heat burst warming descending air mass longer rain cooled smaller clouds found ahead line clouds result clouds having area minor instability ahead main line multi cell thunderstorms dissipate weak shear force poor lifting mechanisms considerable terrain lack daytime heating gust associated line scale area low pressure leading weakening cold essentially thunderstorm exhausted purely dominated system areas dissipating line thunderstorms regions low cape low humidity insufficient wind shear poor dynamics upper level low filling leading general line occur winds decaying time outflow boundaries weakening substantially clouds losing thickness characteristics leading area line composed primarily multiple singular regions rising ground level highest extensions water building dark ominous cloud noticeable thanks scale winds chaotic nature pressure important pressure pressure thunderstorms noteworthy rapid lower mid levels mature thunderstorm create distinct pressure thunderstorms organized lines northern end line commonly referred cyclonic end southern rotating northern hemisphere force northern end evolve creating shaped wake low continue like pattern ahead line create line produce wind shear wind shear important aspect line low medium shear environments mature thunderstorms contribute modest amounts help create leading edge lifting mechanism gust high shear environments created opposing low level jet winds winds intense common cold air outflow leaves trailing area line mid level jet aids processes severe weather severe lines typically bow formation stronger high pressure system convective area strong descending motion line come form pressure difference high lower pressures ahead line cause high winds strongest line indication presence severe weather line line echo wave pattern special configuration line convective storms indicates presence low pressure area possibility damaging winds large hail tornadoes low pressure area contain tornado response strong outflow southwest low portion line outward forming bow echo lies high pressure area depiction maps lines depicted national_weather_service surface analyses alternating pattern red dots dash labelled line variations spanish meaning straight widespread long lived violent induced straight line associated fast moving band severe thunderstorms usually taking form bow echo blow direction movement associated storms similar gust wind sustained generally increases strength gust warm weather phenomenon occur summer august northern hemisphere occur time year occur frequently night daylight hours traditional criteria distinguish severe thunderstorm sustained winds miles hour storm opposed gusts high rapidly increasing forward speed geographic extent typically nautical miles length addition distinctive appearance radar bow echo unique features rear notch vortex usually manifest storms commonly occur north_america occur world outside north_america called different names example bangladesh adjacent portions india type storm known progressive
Squall line