Synoptic patterns associated with heavy rainfall events in the western and southwestern mesoregions of Paraná State, Brazil

Abstract

This study presents a synoptic classification of heavy rainfall events in the western and southwestern mesoregions of Paraná State between 2000 and 2022. A total of 178 cases were identified, characterized by daily precipitation accumulations exceeding 32.8 mm. The classification revealed four principal synoptic patterns associated with heavy rainfall events in the study region. Two of these patterns were linked to the passage of a cold front, while the remaining two were tied to cyclogenetic processes. All four patterns exhibited northwesterly winds at the surface level beginning two days prior to the occurrence of the heavy rainfall event. The Northwestern Argentinean Low and Chaco Low were identified as the main meteorological systems that advect warm, moist airflow into the study region. All four synoptic patterns showed the development of convective systems starting one day before the occurrence of a heavy rainfall event in the study region. Among them, the synoptic pattern associated with a cold front featuring a zonal displacement exhibited the most intense convective activity around the study region, as indicated by brightness temperatures below 240 K. The synoptic pattern associated with cyclogenesis and with a blocking configuration showed surface cyclonic circulation as early as the day before the occurrence of the heavy rainfall events, leading to increased surface mass convergence. This mechanism contributed to intensified rainfall in the study region, underscoring the role of low-level vorticity in sustaining heavy precipitation.