Soil Moisture Gradients and LU/LC Boundary Impacts on U.S. Northern Tier Derechos

A derecho is a convectively-induced windstorm produced by an extratropical mesoscale convective system (MCS) with winds that exceed 25ms-1. Fourteen derecho regions, or corridors, exist in the U.S. The Northern Tier corridor includes derechos that typically track northwest to southeast from the North Central Plains and the Upper Midwest, through the mid-Atlantic states. Development occurs in North Dakota, South Dakota, Nebraska, Minnesota, Iowa, Missouri, Wisconsin, Illinois, Michigan, Indiana, Ohio, and parts of adjacent states. The Northern Tier corridor produces more frequent and more damaging derechos than those initiated in other U.S. corridors. To better understand why this derecho-generating corridor is so productive, I analyze soil moisture gradients (SMGs) and land-use (LU) and land-cover (LC) boundaries in the U.S. North Central Plains and Upper Midwest, in conjunction with synoptic map data. Derecho initiation and intensification stages are defined herein using radar and satellite imagery to describe the derecho development process. Those data permit me to identify 56 summer season (June-August) Northern Tier derechos for 2000-2014, validated against surface high wind reports from NOAA's Storm Prediction Center. Soil moisture data from NOAA's Climate Prediction Center, LU data from the National Land Cover Dataset, and Normalized Difference Vegetation Index LC data help determine the statistical and physical associations of spatial SMGs and LU and LC boundaries on the initiation and intensification of Northern Tier derechos. Results show that spatial SMGs, LC boundaries, and temperature and thermodynamic variables are important for the initiation and intensification of Northern Tier derechos, while LU boundaries show less influence. I use these significant variables to help infer the physical processes underlying derecho development in the Northern Tier; notably, enhanced moisture availability, land cover changes, and synoptic setup. This research enhances our understanding of how spatial variations in boundary layer climates related to SMGs and LC boundaries contribute to severe storm initiation and intensification.

Key words: derecho, soil moisture gradients, land use, land cover, high wind reports, boundary layer climate