Date of Award
Bachelor of Science
Atmospheric and Environmental Sciences
High shear / low CAPE (HSLC) environments are common in the Northeast US and can occur at any time of year. Severe weather in HSLC environments is notoriously hard to predict, often catching both forecasters and the general public off-guard. The goal of this project is to help forecasters to identify HSLC environments favorable for severe weather in the Northeast US, and to discriminate between HSLC environments that are supportive of tornadoes versus those that favor straight-line damaging winds (SDW). A 10-year HSLC severe weather environmental climatology was created for the Northeast US (New England, New York, New Jersey, Pennsylvania). This climatology includes 54 different parameters that can be used to identify and describe severe weather environments. HSLC criteria was defined as surface-based CAPE (SBCAPE) ≤ 500 J kg−1, most unstable parcel CAPE (MUCAPE) and mixed-layer CAPE (MLCAPE) ≤ 1000 J kg−1, and 0–6-km wind shear ≥ 18 m s−1 (Sherburn et al. 2016). Events included in the climatology consisted of numerous (≥5) straight-line damaging wind reports, or at least 1 tornado report. Each event was classified by the season in which it occurred and the mode (discrete, cluster of cells, quasi-linear convective system (QLCS)) of the storm which produced the reports. Results show that warm-season HSLC severe events typically occurred either at the beginning or at the tail end of an event in an environment where CAPE values were predominantly too large to meet the HSLC criteria. Storm mode was variable for warm-season events, but cool-season events were dominated by QLCSs. Results show lifted condensation levels (LCLs) as well as low-level shear and wind direction as some of the most skillful parameters at discriminating between tornadic and non-tornadic events. There are various other useful parameters, including but not limited to, surface relative humidity, effective shear magnitude, and convective inhibition. The usefulness of these, and other parameters, at discriminating between HSLC environments favorable for SDW versus tornadoes will be discussed.
Main, Michael E.; Lazear, Ross A.; and Bosart, Lance F., "Differences Between High Shear / Low CAPE Environments in the Northeast US Favoring Straight-Line Damaging Winds versus Tornadoes" (2018). Atmospheric & Environmental Sciences. 15.