Analysis of an Extreme Precipitation Episode over the Central Subtropi-cal Andes using the ETA-PRM Regional Model

MAXIMILIANO VIALE; FEDERICO A. NORTE

Santa Fe, New Mexico, U.S.A.

Congreso; 12th Conference on Mountain Meteorology; 2006

American Meteorological Society

The aims of this study are to analyze the thermodynamics, synoptic, and mesoscale conditions for a heavy rain and snowstorm event occurred during 26-29 August 2005 over the Central Andes of Argentina and Chile; and to evaluate the ETA-Programa Regional de Meteorología (PRM) regional model as a potential forecasting tool. It is mainly intended to determine the potential of the model to capture mesoscale-topography conditions related to extreme precipitation accumulated on the western slopes and high-mountain of central Andes and to the orographic winds (Zonda /chinook/foehn wind) on the eastern slopes. This episode caused floods in Santiago city with many houses overflowed and hundreds of people damaged; the main international roadway was closed during many hours; and strong Zonda wind gusts were observed over the plains of San Juan province in Argentina. The principal synoptic conditions during August 27th when the EPE?s maximum intensity occurred were: Absence of a clear trough in the middle and high levels (as typical cases) and absence of an intense surface extratropical cyclone. Persistence of a wide low pressure belt (35ºS-50ºS) linked to a high pressure blocking area in the higher latitudes (55ºS-65ºS). The ETA-PRM model is hydrostatic and uses the eta vertical coordinate. The model is integrated with horizontal resolution of 15 km and 38 vertical levels over the central Chile and central-western Argentina region. The model integrations began 48h -72h before the maximum event intensity; and the initial condition and the lateral boundaries were taken from the ETA-Centro de Previsao de Tempo e Estudos Climáticos (CPTEC-Brazil) South American continent version analysis. The model was able to forecast heavy liquid and solid precipitation and starting and ending precipitation times. The ability to reproduce the zonal precipitation gradient across and on both slopes and the Zonda wind on the downslopes of the Central Subtropical Andes provides successfully confidence in the model.