The advection of warm, moist air by an LLJ, sometimes accompanied by cold advection in the upper-level jet stream, provides a source of instability and promotes long-lived … Part I: Climatological Distribution ROBERT J. TRAPP Purdue University, West Lafayette, Indiana SARAH A. TESSENDORF Colorado State University, Fort Collins, Colorado ELAINE SAVAGEAU GODFREY University of Oklahoma, Norman, Oklahoma HAROLD E. BROOKS National Severe Storms Laboratory, Norman, Oklahoma (Manuscript received 10 February … Squall lines also typically have an area of stratiform rain that trails the main line of thunderstorms (called the "trailing stratiform" region), although depending on how the upper-level winds are blowing, the area of stratiform rain occasionally is ahead of the squall line or even parallel to it, so there's more than one flavor of squall line!! A large part of how squall lines manage to produce tornadoes is in the type of cell contained within the squall line. High pressure built into the region as July set in, putting an end to the summer tornado season. While the squall line strengthens, the tornado threat for the Big Bend may be diminishing. Squall lines are observed frequently in the warm sector of a midlatitude cyclone, usually about 100–300 km in advance of the cold front. Divergence ahead of an upper-level trough induces low-level convergence. If you have a continuous squall line that has propagated itself and consists of not individual cells, but of one long strip of thunderstorms - then the chances of getting a tornado out of that mess are non-existant. WARNING: HERE'S THE DIFFERENCE Two tornadoes were recorded in late June, with an EF1 squall line tornado tracking through northern Muscatine and a brief landspout touchdown taking place in Webster County. Tornadoes from Squall Lines and Bow Echoes. However, if you have a squall line that is comprised of … SEVERE THUNDERSTORM WATCH VS. The tornado that hit midtown Tulsa on Aug. 6, 2017 — an EF2 that injured 30 people and damaged or destroyed 129 business and 19 homes — was part of a squall line, Calianese said. A squall line is a group of thunderstorms arranged in a line that produces heavy rain and strong winds. "Squall lines tend to pass quickly and are less prone to produce tornadoes than are supercells," the NSSL notes. Within strong squall lines tornadoes can form.