Forecasting the occurrence of L-band scintillations has been a challenging task and, this challenge has been tackled by evolving a simple method using GPS-TEC data. For given background conditions, it has been shown that the fluctuations in the GPS-TEC truly represent the characteristic features of the perturbations that are responsible for the initiation of the plasma instability that finally culminates in to the observed irregularities. The close linkage between the perturbation features and the evolutionary pattern of the scintillations enable us to forecast ‘when’, and ‘for how long’ the L-band scintillations would occur, in addition to their ‘occurrence pattern’. The first of their kind of results take us a step closer towards operational forecasting of L-band scintillations for real time navigational purposes.