SEVERE WINTER STORMS OVER THE WESTERN AND CENTRAL STATE OF SÃO - PAULO, BRAZIL - Ana Maria Gomes and Gerhard Held - Case study (15 September 2009)

Sep 8, 2026

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Severe winter storms over the western and central Brazilian state of São Paulo are analyzed using two S-band Doppler radar datasets from IPMet. The study focuses on anomalous storms during July 2007, including a case study for 24 July 2007. It quantifies hail-producing cell properties and precipitation fields exceeding 300 mm, using the TITAN system and its tracking and climatological modules, with reflectivity and volume thresholds to derive storm tracks, duration, and radar-based rainfall distributions relevant for agriculture and water planning.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages2

Reading Time5 min

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I. INTRODUCTION

II. PRESENTATION OF RESEARCH

III. RESULTS AND CONCLUSIONS

SEVERE WINTER STORMS OVER THE WESTERN AND CENTRAL STATE OF SÃO PAULO, BRAZIL Ana Maria Gomes and Gerhard Held Instituto de Pesquisas Meteorológicas-IPMet, São Paulo State University-UNESP, Bauru-Brazil, [ana@ipmet.unesp.br](ana@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, in general, characterized by summer rain and relatively dry winter months. The region is under the influence of both tropical and mid-latitude, large-scale synoptic systems. Severe thunderstorms can occur at anytime of the year, although they are less frequent during the dry winter months. Most of the significant weather occurs between October and March, when the supply of solar energy and humidity is greatest, but severe winter storms, usually associated with baroclinic systems, do occur within the range of IPMet´s two S-band Doppler radars, which covers most of the State of São Paulo. This study presents an analysis of the anomalous winter storms during July 2007, which have produced considerable damage over parts of the State, as well as a precipitation field in excess of 300 mm over its central and western regions. A case study for 24 July 2007 is presented, focusing on the storm properties related to the hail-producing cells and the hail metrics parameters of the NCAR software TITAN (Thunderstorm Identification, Tracking, Analysis and Nowcasting; Dixon and Wiener, 1993) . The data used for the analysis were from IPMet´s two 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 16 elevations (0.3° to 45°), 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. 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 TITAN system in ARCHIVE mode was deployed and tracking properties form the base for the analysis presented here. A TITAN cell was defined by the 40 dBZ threshold for the reflectivity and 50 km3 for the volume, observed at least in two volume scans (15 minutes) . The total rain field observed by IPMet´s radars for July 2007 was obtained using the climatological module of TITAN that computes geographically-distributed statistics from TITAN storm and track files. The TrackGridStats application has produced analyses of storm tracks for all periods with storm activity during July 2007. To derive the spatial distribution of storm precipitation and storm duration during July 2007, the storm areas were defined by the 25 dBZ reflectivity threshold, and all identified areas that exceeded the adopted threshold within the quantitative range of both radars, were considered. III. RESULTS AND CONCLUSIONS Synoptic Overview for July 2007 During July 2007, at least seven transient systems were observed over Brazil and five of these systems were frontal waves that had originated in the south and southeast regions (CPTEC, 2009), producing some of the very favorable large-scale environments, such as frontal systems and high-level cyclonic vortices that were all enhanced and have generated the extreme events observed in the State of São Paulo. An anomalous precipitation field between 200 and 300 mm above the expected mean over the central and western regions of the State was observed (Figure 2), changing completely the spatial distribution of rainfall for this relatively dry month, which is characterized by average rainfall within a range of 20 to 30mm for most of the State of São Paulo, except in the south and costal areas. FIG 2: Precipitation anomaly for July 2007. Modified from CPTEC (2009),

FAQs

What geographic area and season are studied for severe winter storms?

The study covers the western and central parts of São Paulo state, Brazil, focusing on anomalous winter storms observed during July 2007.

Which tools and radar data support the storm analysis?

Analyses use IPMet’s two S-band Doppler radars (Bauru and Presidente Prudente) and the TITAN software, including its ARCHIVE and climatological modules for storm tracking and precipitation statistics.

How were storm tracks and precipitation distributions derived?

Storm tracks were defined using TITAN cell thresholds and rain-field statistics from storm and track files, while spatial precipitation and storm duration were obtained using a 25 dBZ reflectivity threshold within the quantitative radar range.

Sep 8, 2026

Upload by Levi