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The 'Convective Storm Initiation Project' (CSIP) took place in summer 2005 in the maritime climate in the South of England, to study why convection breaks out precisely where and when it does. Despite the dense radiosonde network deployed during the CSIP campaign, aircraft measurements demonstrated that the high spatial variability of the temperature and especially of the water vapour field based on radiosonde data alone was not well resolved with respect to the detection of the initiation of convection. This investigation focuses on the impact of an increased resolution of thermodynamic and dynamic variables of the planetary boundary-layer on the detection of the initiation of convection. The enhanced spatial resolution was obtained using the synergetic effect of the combined use of data from the radiosonde network, automatic weather stations, synoptic stations, and especially from GPS stations. This data set was used to calculate convection-related parameters, which quantify the atmospheric stability, convection inhibition and triggering of convection. The gained spatial resolution and the combination of convection-related indices successfully revealed the areas where the probability for deep convection was high on 29 June, 2005 (IOP5). Location and timing of the initiation of convection were critically influenced by the structure of the humidity field in the boundary-layer. On the one hand the initiation of convection was better detected by lifting a near-surface parcel to calculate the convection indices whereas on the other hand the subsequent development into deep convective cells was better represented using a mixed-layer parcel for lifting. The altitude, strength and persistence of stable layers were observed to be important for the initiation of convection. When initiation took place, very low convective inhibition (CIN) of <15 j kg−1 was observed in the whole investigation area. Additionally, the role of boundary-layer convergence was decisive even in this low CIN environment. Moreover, convergence and CIN influenced the triggering of storms more than convective available potential energy (CAPE). However, the storm intensification was dominated by CAPE and high mid-tropospheric moisture.