Radar Morphologies For Severe and Non-Severe Thunderstorm Days in Northern New England

The nature of convective morphologies in northern New England was examined for warm season (April – September) thunderstorm days for the period 2011-2016. The relationship between the 700 hPa wind direction and morphology frequency was also examined. Thunderstorm days were identified by using METAR reports from 26 stations (within 125 nm of Fryeberg, ME - KIZG) across New Hampshire, Maine, and Northeastern Massachusetts. Thunderstorm days occurred when the METAR report contained the codes of LTG (lightning), TS (thunderstorm), or LTG DSNT (lightning distant). Days were further categorized into severe and non-severe thunderstorm days, where severe thunderstorm days were associated with a Storm Prediction Center event report. Northeast U.S. composite archived radar reflectivity data from the National Center for Atmospheric Research (NCAR) Mesoscale and Microscale Meteorology Laboratory (MMM) Archive and the Gray, ME (KGYX) National Centers for Environmental Information (NCEI) (Next Generation Weather Radar (NEXRAD) Level-II Archive was used to assign a convective morphology as defined by Gallus to every METAR report. All thunderstorm days were assigned one or more morphologies per day. To further investigate the relationship between wind direction and convective morphology, the 0000 UTC sounding from KGYX was used to assign a 700 hPa flow direction for each thunderstorm day.

The most frequent morphology type was isolated cells (IC) on both severe and non-severe days. July had the highest number of thunderstorm days, resulting in the highest frequency of all morphologies on severe days. August had the highest frequency of all morphologies on non-severe days. An interesting contrast was found between broken lines (BL) and clustered cells (CC). BL’s occurred more frequently than CC on severe days, however, CC occurred more frequently than BL on non-severe days. When analyzing flow direction, BLs occurred with the same frequency (about 19%) on non-severe days with southwest and west flows. Trailing stratiform (TS) also followed this same pattern on severe days. It was further concluded that East and Southeast flows did not occur at all on severe days, only being present on non-severe days.