This study analyses the relation between the Streams/Low-Level Jets (LLJ) at the 850 and 950 hPa levels with the "K" Index. The mechanism associated with the Streams/LLJ transports the heat and water vapor, increasing the humidity in the low troposphere. This humidity in the low troposphere to affect directly the "K" Index. Profiles of air temperature and dew point were used by radiosonde measurement at Salgado Filho International Airport in Porto Alegre. The "K" Index was calculated at 21:00 and 09:00 hrs, local time, during 176 days and compared with daily precipitation in Porto Alegre. To describe the relations involved, the study uses statistical method non-hierarchical classification to separate the cluster data of the time series that characterize the variety of the K's Index with the precipitation. The result display to be important of the transport by Streams/LLJ at the 950 hPa; it characterizes a mechanism of the convergence and to produce the convection in the Planetary Boundary Layer (PBL).
streams; planetary boundary layer and "K"index
