Abstract
Abstract. During the afternoon of 4 October 2007, a thunderstorm swept across the Island of Mallorca from southwest to northeast. Strong straight-line winds (up to 30 m/s) and heavy rain (rates up to 100 mm/h) were registered accompanying the storm. Tornadoes with an estimated intensity of F2–F3 developed nearby the city of Palma, severely affecting industrial installations. One person was killed by the impact of heavy debris while more than 10 million € in damages were attributed to the event in the industrial area only. The observed evolution of temperature, humidity, wind and pressure, as well as the sequence of radar images, reveal that a squall line was initially organized over the sea and then moved north-eastwards at an estimated speed of around 80 km/h. This paper presents an analysis of the event from an observational point of view. The aim of the study is to contribute to the characterization of these rare events in the Western Mediterranean by analyzing the observational information available for this particular extreme event. The diagnosis is aimed at helping forecasters to identify this kind of organized deep convective events and being able to issue timely warnings. The synoptic scenario shows warm and moist advection at low levels over Balearics and an upper-level trough over mainland Spain. This situation is known to be prone to deep convection in Mediterranean Spain in autumn. Radiosonde ascents from Murcia and Palma show convective instability at mid levels that can conduce to develop convection if appropriate ascents occur. A plausible lifting mechanism to trigger convection is attributed to large amplitude gravity waves, registered as short-period pressure oscillations by surface barographs.
Highlights
The Balearic Islands, located at the centre of the western Mediterranean (Fig. 1), are known for their pleasant weather, especially during the warm period of the year
A recent heavy rain event occurred on 15–16 December 2008, when more than 250 mm in 24 h were collected in several sites in the mountainous area of Mallorca
(top) and sferic information of lightning strokes between 15:40 tection network shows a linear structure of the lightning 5 MeteUoTrColo(bgoicttaolmsi)tuation overview strokes when the disturbance arrived in Mallorca (Fig. 6). Information from both radar and LINET networks 5.1 Synoptic overview adds upon the evidences that the convection of 4 October was organized as a squall line
Summary
The Balearic Islands, located at the centre of the western Mediterranean (Fig. 1), are known for their pleasant weather, especially during the warm period of the year. A post-storm damage survey indicated the plausible event is that the severe convection developed and evolved scenario of one or more coexisting tornadoes of F2–F3 inover the sea, whereas the previous cases reported occurred tensity, which affected an industrial area located to the northover land. Regarding the passage of the storm, a decrease of the pressure followed by a quick increase and posterior decrease were observed Such characteristic signature matches the scheme of a pre-squall mesolow, shortly preceding the onset of heavy rain and strong winds, followed by a post-squall mesohigh (Johnson and Hamilton, 1988). Such pressure distribution was observed in the squall line that crossed north-eastern Spain in 1993 (Ramis et al, 1999). Such speed appears to be in the upper range of the typical speeds observed for squall lines with bow echo structure (greater than 65 km/h)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
