Study of the September 17th 2007 severe hailstorm in Pla d'Urgell. Part II: meteorological analysis

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DOI: 10.3369/tethys.2009.6.06

pp.: 83 - 103


During the afternoon of September 17th 2007 a severe hail event occurred in the Pla d'Urgell region. The storm brought hail larger than 5 cm in diameter, which was registered in 81 hailpads from the hailpad network existing in the region. According to these records, such episodes are unusual, as hail episodes in September are usually smaller in extension and diameter. Farnell et al. (2009) have analyzed the damage caused by this episode, while this second part of the study analyzes the meteorology of synoptic and mesoscale patterns. The analysis is based on the remote sensing data (satellite, meteorological radar, lightning detection, radiosonde) from the Meteorological Service of Catalonia. The synoptic conditions of the analyzed episode were favorable to convection, with a trough at high levels near the studied area, associated with a low over Scandinavia. Meteosat imagery showed how the hailstorm was part of a Mesoscale Convective System, which originated in the center of the Iberian Peninsula and moved NE, producing hailstorms in the NE of the Iberian Peninsula and in the south of France where there were also heavy hailstorms. V-notch and hook signatures can be identified in the radar product just before and at the moment of the severe storm. However, this storm can not be defined as a supercell (no mesocyclone was detected). Radar analysis also showed that maximum vertical developments were located in the region where the larger hailstones were observed on the ground. Finally, the lightning data analysis showed how lightning activity attained intensities characteristic of severe weather.

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Partially funded through grants CGL2007-29820-E/CLI, CGL2008-02804-E/, CGL2009-07417-E and CGL2011-14046-E of the Spanish Ministry of Science and Innovation