Heavy precipitation event (HPE) recording the rainfall accumulation greater than 130 mmoccurred during IOP 15a in the northern Spain region. With the aim to clarify thecharacteristic, transport, and role of water vapour patterns to the HPE, the intensive fieldobservation was successfully carried out. Using the observational dataset of SAFIRE/ATR42airborne water vapour lidar LEANDRE2, ground-based lidar WALI, ground-based GPSnetwork, rain gauge network, and SEVIRI satellite, together with AROME-WMED data, inthis study, we investigate the multi-scale interactions between the moist-air flow and deepprecipitation during IOP 15a. The analysis of AROME-WMED fields showed that the lowlevelwind convergence of easterlies and south-easterlies with 10−12 m s-1 wind speed wascontinued in the north-eastern coastal region of Spain (Catalonia, CA) during 19-20 October2012. With the low-level south-easterlies, the supply of high mixing ratio of water vapourgreater than 14 g kg-1 from the northwestern Mediterranean Sea to the CA region wascontinuously captured. In this environment, the surface rain gauge network recorded therainfall in the CA region, steadily from 04 UTC on 19 October to 22 UTC on 20 October.During the same period, the ground-based GPS (2.0°E, 41.4°N) steadily recorded therelatively-large amount of integrated water vapour of 36−43 kg m-2. The SAFIRE/ATR42travelled the upstream of the HPE two times: AS52 from 0954 to 1256 UTC, and AS53 from1414 to 1519 UTC on 20 October. As it approached to the upstream of HPE, a layer havingthe water vapour greater than 10 g kg-1 ascended from below 0.4 to 1.1 km; simultaneously,the maximum water vapour increased up to 14.5 g kg-1. These well-captured low-level watervapour characteristics in the upstream of HPE during IOP 15a and its dynamical interactionwith the HPE development will be introduced at the conference.