A comparison was conducted between warm-season and cold-season inverted trough (IT) cases in the central US. Inverted troughs are observed throughout the year in the mid-latitudes on the leeward side of north-south oriented mountain ranges. Inverted troughs appear as poleward bulges of low pressure on surface pressure contour maps and can act as a third front on a mid-latitude cyclone, separating two different polar air masses. Previous work conducted on ITs has focused on cold-season cases and their potential to produce heavy snowfall, however little work has been done during warm-season. However, ITs have also been associated with severe weather, and in particular, flash flooding during the warm-season.

Case studies were conducted on both a warm-season and cold-season IT in the central US and compared to cold-season examples from previous work done by Keshishian et al. (1994) and Weisman et al. (2002). The central US, as defined for this project, is roughly between the Rockies and the Mississippi River within the boundaries of the U.S. A search of daily surface maps from 2000 to 2006 turned up numerous examples of ITs at all times of the year. One representative warm-season and one cold-season IT were selected for study. For the warm-season case, 1200 UTC 1 June 2003 through 1200 UTC 3 June 2003 was selected. The cold-season case occurred from 0000 UTC 28 December 2006 to 1200 UTC 31 December 2006. North American Regional Reanalysis (NARR) data were obtained from the National Climatic and Data Center (NCDC) at six hour time steps for the each case study with an extra 24 hour period added on either end. Comparisons were performed at the surface, 850 hPa, 700 hPa, 500 hPa and 250 hPa .

Through the case study process, it was determined that both the warm and cold-season ITs by in large form and progress in a similar manner. The troughs hold a similar shape and amplitude during both seasons, and precipitation falls in the same region relative to the low pressure center. The largest contrasts between the two ITs are that the cold-season case produced solid, rather than liquid precipitation, and also has a noticeably stronger pressure gradient than the warm-season IT, as would be expected. Although the two cases presented show a strong parallel between warm and cold-season ITs, more cases need to be studied before firm conclusions can be established. Additionally, understanding of ITs would benefit from a year round climatology of their frequency. Further work on a larger number of cases is needed to better comprehend the difference between the two seasonal ITs.