Active Weather Pattern for the West into the Plains

A strong Pacific storm continues to track across the Great Basin. Heavy snow is expected across the higher elevations and heavy rain across lower terrain. Strong gusty winds will make for additional hazards for travelers. These winds will bring increasing fire weather concerns for the southern High Plains. Then we will closely watch for severe thunderstorms across the central Plains on Monday. Read More >

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Our observations and experiences of squall lines and bowing convective systems which produce widespread damaging winds always facinated our group since our early years. Since many of our members originally came from the Great Lakes region, the Midwest and the northeast sections of the U.S. we experienced a number of these systems, during the our lifetimes, and took special interest in the study of the squall lines and bow echoes. The primary goal of our study is to further understand the many components of the squall line and improve our prediction of damaging straight-line winds and non-supercell tornadoes. This year we are collaborating with Dr. Nolan Atkins (Lyndon State College) and Dr. Jeff Trapp (Purdue University). Our study of squall lines and bow echoes began with the 2 July 1992 event across central and eastern Missouri and continue with the many bowing MCSs which occurred during the 1998 and 2000 spring convective seasons. In nearly eightly percent of our cases studied from 1992 to the present, comprehensive damage surveys were conducted by the SOO at WFO LSX , other NWS personnel from WFO St. Louis and graduate students from Saint Louis University. We focused our work to find relationships between storm reflectivity-velocity structures / convective-scale vortex evolutions and damage observed during a ground survey.

Concerning tornadic damage with squall lines and bow echoes, we specifically focused our work on the evolution of gamma-scale (convective-scale) vortices. Where they initially form with respect to low-level boundaries and locations along the bow. Since last year (2002), we have collaborated with Dr. Nolan Atkins at Lyndon State College on the study of gamma-scale vortices associated with QLCS and bow echoes. Today we are working with Nolan, Chris Bouchard from Lyndon State and Jeff Trapp from Purdue University. The 1998 and 2000 convective seasons combined were extremely busy with 14 MCSs recorded over the Mid-Mississippi Valley region. The 2001 convective season was relatively quite. However, we were able to capture four convective line cases during the spring 2002 convective season. Two significant events occurred during this year (May 6 and June 10). Both of these events are currently under study and will be included in our data stratification. Our preliminary studies showed that our greatest threat for widespread wind damage across the Mid-Mississippi Valley Region occurred during the months of May and June. Two graphics one the first page of the Damaging Winds Website shows a preliminary data stratification of MCS events across the Mid-Mississippi Valley Region. We additionally updated the pre-convective environment page showing the degree of CAPE and magnutide of Bulk Shear for the 0-3 and 0-5 km layers. Thus far we have completed the study of twenty-six MCS events with four events under investigation. Some of the web pages are still under construction or are currently being updated.

Ron Przybylinski (SOO / WFO St. Louis)
Gary K. Schmocker (Forecaster / WFO St. Louis)
August 2003

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