Analisis y diagnóstico de episodios de meteorología severa en el País Vasco

Abstract

The atmospheric processes prior to and during the outbreak of 2 galernas (July 25, 1995 and May 30, 1996) are analyzed. Data from surface stations, meteorological satellites, the Punta Galea wind profiler radar and numerical simulations with the mesoscalar model RAMS are used. It is concluded that the origin of the classic galerna of the warm season is associated with the irruption of a cold front on the N coast of the Iberian Peninsula. This front, which in most cases is not recorded on the synoptic weather charts, is associated with the presence of a low-pressure N-to-S trough between a European anticyclone and the Azores anticyclone. The surface front is preceded by an intense Foehn on the north coast, which is clearly visible in the satellite images, and which causes high temperatures on the Basque coast during the morning. The frontal advection over the land mass of the northwestern half of the peninsula can leave precipitation on the W-coast and southern slopes of the mountains in Galicia (galerna of July 1995). However, over the sea, a relative cold marine boundary (MBL) layer is transported parallel to the coast from Galicia (with colder water) to the Basque coast (with warmer sea surface temperatures). It runs parallel to the coast and remains uncoupled from the south-westerly winds, which cross over the Cantabrian Mountains and blow above the MBL. The decoupling is caused by the temperature inversion associated with the cold advection of the MBL and the presence of the Cantabrian mountain range. On the Asturian coast, protected by the highest mountains, the cold coastal advection and solar heating of the slopes, cause sea-land and up-slope breezes (Avilés weather station). An intense convergence occurs at the top of the Cantabrian mountain range: SW winds that blow on its S slope and those from the NW associated with the combined sea and up-slope breezes. Data from the wind profiler radar at Punta Galea (Getxo) documented a galerna depth of 1,500 meters and intense winds from the SW blowing above, confirmed by numerical simulations with the RAMS mesoscale model (3 km horizontal resolution and 1 hour resolution).