A Multi-Scale Study of the 23 October 2022 Southern England QLCS

During the afternoon of 23 October 2022, a quasi-linear convective system (QLCS) developed and intensified over the English Channel and tracked north-northeastward into southern England, producing widespread damaging downburst winds. The most intense downbursts of the event occurred at 1) Army Aviation Centre (AAC) Middle Wallop, Hampshire (55 miles SW of London), with a wind gust of 54 kt (62 mph) recorded between 1500 and 1600 UTC and generated by a prominent bowing segment of the QLCS; 2) London Colney, Hertfordshire, with a wind gust of 56 kt (64 mph) recorded at 1640 UTC and generated by a pulse-severe cell east of the bowing segment of the QLCS. In general, as shown in Figure 1, the early afternoon (1222 UTC) NOAA-20 NUCAPS sounding qualitatively indicated the strongest signal for severe thunderstorm and downburst occurrence over southern England: 1) It resolved a shallow elevated mixed layer detected by the closest downstream RAOB sounding at Nottingham; 2) Indicated more significant lower-middle tropospheric temperature lapse rates and CAPE than the adjacent AIRS sounding; and 3) NUCAPS surface temperature (66°F/18°C) matched the temperature recorded at Herstmonceux, the closest observing station to the retrieval. Mapped SSMIS imagery with UKMO rain radar overlays and a mid-day NUCAPS sounding profile over Leicestershire (~90 miles NW of London) provided the strongest signal for severe downburst winds in the pre-storm environment over the Midlands. Close agreement is noted between the boundary layer structure ("inverted-V") as resolved by the NUCAPS soundings and WRF profiles and the MWPI gust potential calculated from NUCAPS and the WRF model. A strong relationship between high rain rates, as indicated by UKMO radar, and the very low MW brightness temperatures (BTs) is apparent in both the consecutive F-18 and F-16 overpasses. Low BTs also correspond well with the high integrated graupel values, suggesting that intense downdrafts and resulting downbursts were forced by ice precipitation loading and melting and unsaturated air entrainment into the mixed-phase precipitation core. In addition, a trailing stratiform precipitation region with possible embedded elevated convective storm cells enhanced the severity and longevity of the QLCS during its track through the greater London area and southeastern England. The favorable thermodynamic and dynamic factors revealed in this study warrant further investigation into the potential role of elevated convection and the development of a rear-inflow jet during the most intense phase of the system. Comparison of LEO satellite microwave imagery to Doppler radar reflectivity patterns and cross-sections of WRF-model derived thermodynamic parameters (i.e., equivalent potential temperature) should further strengthen the evidence for QLCS structure and the presence of a rear-inflow jet.