5 h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY PREDICTABILITY OF EXTREME STORM EVENTS IN THE STATE OF SÃO PAULO, BRAZIL Gerhard Held , Ana Maria Gomes, Mateus Teixeira, José Marcio Bassan and Geórgia Pellegrina Instituto de Pesquisas Meteorológicas-IPMet, São Paulo State University-UNESP, Bauru, Brazil, gerhard@ipmet.unesp.br (Dated: 15 September 2009) I. INTRODUCTION The State of São Paulo is situated in the south-eastern region of Brazil and is characterized by summer rain and relatively dry winter months. However, severe storm events can occur any time of the year, but during summer they have a more tropical character, while from about mid-April to September they are usually associated with baroclinic synoptic situations and cold fronts advancing from southern Brazil in a north-easterly direction into the western and central State of São Paulo. The Meteorological Research Institute (IPMet) of UNESP operates two S-band Doppler radars, located at Bauru (Lat: 22°21.5’ S, Lon: 49°1.7’ W, 624 m amsl) and Presidente Prudente (Lat: 22°10.5’ S, Lon: 51°22.5’W, 420 m amsl), respectively (Figure 1). The main characteristics of both radars are: 2° beam width, 450 km range for surveillance mode and 240 km in volume scan mode, with 11 (15) elevations from 0.3° to 35°, 1 km (250 m) radial and 1° azimuthal resolution, and a temporal resolution of 15 minutes or less, recording and archiving reflectivity, radial velocity and spectral width (numbers in brackets are applicable from 2007). FIG. 1: Doppler radar network of IPMet (BRU = Bauru; PPR = Presidente Prudente), showing the 240 and 450 km range rings. II. PRESENTATION OF RESEARCH The most severe 7 events during the last five years (2004 – 2008) had been selected to verify their predictability from about 48 hours before the occurrence up to the nowcasting time scale of 30 – 60 min before reaching a town, city or industrial installations, like high-voltage power lines, etc. IPMet, in collaboration with CPTEC, runs the Meso- Eta model, centered over the Bauru radar, twice daily (initiated at 00 and 12 UT) with a temporal resolution of 3 hours up to 72 hours. Its domain amply covers the State of São Paulo at a resolution of 10x10 km horizontally with 30 levels from 1000 to 100 hPa. This model has been specifically fine-tuned to compute additional convective parameters (SR helicity, BRN Shear, supercell index, etc), as well as the generation of vertical profiles (Skew T – Log P) at any specified grid point (Held et al., 2007). Furthermore, each run of the model is executed twice, using the convection parameterization of Betts & Miller and Kain- Fritsch, respectively (Betts and Miller, 1993; Kain, 2004). In this paper we shall show which of these new outputs are the most suitable for predicting a severe event up to 48 hours ahead of its possible occurrence, which is then used to alert regional emergency services for the possible need of a standby (especially important before weekends). On the day of severe thunderstorm development, NCAR´s Software TITAN is deployed (Dixon and Wiener, 1993), utilizing observations from the two S-band Doppler radars, to issue alerts of possible heavy rainfall, probability of hail or extremely strong winds on the time scale of 60 – 30 min. III. RESULTS AND CONCLUSIONS The following cases had been selected on the basis of severe damage that had been reported in News Papers, on TV, on Websites or documented by the Civil Defence Organization of the State of São Paulo: 27 February 2004, when heavy rain was accompanied by an extremely severe wind storm, resulting in the destruction of about 30 high-voltage transmission towers, as well as damage to more than 50 houses in several small towns. 25 May 2004, when a supercell, lasting 8,5 hours, and two tornado-spawning cells were tracked by IPMet´s radars, causing the death of 2 and severe injuries to 51 people, as well as great damage to sugar plantations. The tornadoes had a strength of F2-3 and F2, respectively, on the Fujita scale. 24 May 2005 was another day, when an F3 tornado was observed, killing one person and totally destroying an industrial suburb and damaging many buildings and structures in other parts of the town, resulting in a total loss of USD 42 million. 29 March 2006, when a strong frontal event provoked the formation of a bow-echo, which generated extremely strong wind gusts at its leading edge (almost tornado-like), causing enormous damage in two towns in the centre of the State. 19 January 2007 marked the occurrence of a small tornado in the western State during the early hours of the morning. It caused damage to some houses, uprooted large trees and destroyed an electric transmission line. 24 July 2007 was characterized not only by the unseasonal heavy rainfalls over the State, but also by a severe hail swath, destroying the orange crop in the NW regions. 29 October 2008, when a microburst near Bauru destroyed 6 high-voltage transmission towers and caused other damage. Detailed case studies of some of these storms have already been presented, analyzing the synoptic situations and radar and lightning observations, using TITAN in Archive mode (Held et al., 2006, 2007b; Gomes and Held, 2006, 2009) and simulating a forecast between 30 and 60 minutes, which can then be compared to the actual situation. There- fore, the findings from the synoptic and radar analysis will only be briefly dealt with in this paper, while the emphasis