Sounding Parameters Associated with Severe and Non-Severe Thunderstorm Days in Northern New England

A previous climatology of thunderstorm days and radar identified convective cells from 2003 to 2007 in the Gray, ME (KGYX) radar domain concluded that convective weather was most prevalent with a Southwest upper-level flow direction. The goal of the current study is to identify thunderstorm days from a more recent five-year period. This analysis investigated a five-year (2011 – 2016) climatology of warm-season (April – September) thunderstorm days in northern New England within 125 nm of Fryeburg, Maine (KIZG) to investigate upper-level (700hPa) flow directions and sounding parameters associated with severe and non-severe thunderstorm days. Using archived METARs from the Iowa State Mesonet archive, thunderstorm days were identified if the reports contained LTG (lightning), LTG DSNT (distant lightning), or TS (thunderstorm) codes. Severe weather days were identified using the Storm Prediction Center's severe weather reports. Sounding parameters and wind speeds and directions for the surface, 925, 700 and 500 hPa were recorded for the KGYX sounding closest in time to the METAR from the University of Wyoming’s radiosonde archive.

Results found that Southwest and West flow at 700 hPa were the most common on both severe and non-severe weather days confirming similar to previous research. Mean sounding stability parameters typically showed a decrease in stability (e.g., higher CAPE, lower Lifted Index, higher Total Totals) on severe days than non-severe days. However, mean mid-level (700 – 500 hPa) lapse rates were not statistically significant on severe days compared to non-severe days. Mean wind shear values for surface to 850hPa and surface to 500hPa did not differ from one another. Statistically, the differences in mean wind shear for all layers were insignificant. The distribution of CAPE and CIN values showed a distinct skew toward lower values with many soundings often reporting values of 0 J/kg. It is hypothesized that morning inversions and afternoon sea breezes at KGYX contribute to this finding.