Long-term changes in the climatology of transient inverted troughs over the North American Monsoon region and their effects on severe weather

Transient inverted troughs can affect the magnitude of severe weather during the North American Monsoon season through the Southwest Contiguous US and Northwest Mexico. These upper tropospheric disturbances enhance both the synoptic scale and mesoscale convective environments, increasing the chances for microbursts, straight line winds, blowing dust, and flash flooding throughout the region. Due to the growth of the cities of Phoenix and Tucson in recent decades, the human population vulnerable to monsoon related severe thunderstorms is high. This work considers changes in the track density climatology of inverted troughs between 1950 and 2012. Inverted troughs are tracked as potential vorticity (PV) anomalies on constant pressure surfaces from a WRF downscaled regional climate model forced by NCEP/NCAR Reanalysis 1. Changes of the temporal frequency and spatial distribution of inverted troughs during this time period may show the effects of climate change on these dynamically significant features for severe weather in the monsoon region. Quantification of the strength of inverted troughs is also considered in the context of their distribution of maximum PV at 250 hPa. The classification of inverted trough events by the distribution of maximum PV may allow for extreme events to be characterized more easily by operational forecasters. -->