Tropical-like heavy convective rains over the Spanish Mediterranean regions: a radar-based perspective

Heavy rain events are the most important meteorological challenge in the western Mediterranean regions for operational forecasters. These episodes have frequently a convective origin and usually take place in autumn when the maritime waters are much warmer than air and surrounding areas. The convective clouds often evolve to well-organised, long-lived convective systems: Mesoscale Convective Systems, MCS, as well as Mesoscale Convective Complex, MCC. In principle, operational remote sensing systems have enough skill to detect those precipitation systems. However, some heavy and severe rain episodes show special characteristics: the radar reflectivity values are considered "benign", echotops and reflectivity centroide heights are lower than the corresponding warm season ones, VIL imagery does not show the intense values associated with other midlatitude convective systems, the lightning rates are quiet low, even more, no lightning activity is sensed when these torrential rains occur. Operational forecasters may overlook these precipitation systems if they do not use appropriated conceptual models and operational tools.

In this paper, a case-based radar study tries to document the structure of this kind of convective cloud affecting the Spanish eastern coasts. The results obtained from both two and three dimensional radar techniques show how some western Mediterranean convective systems resemble tropical maritime convective clouds and clusters. A redefined convective system conceptual model much closer to tropical latitudes than to middle ones is proposed for this type of event.