One of the most promising solutions of increasing the reliability to accelerate the penetration of the renewable electricity in the power sector worldwide is to reduce the uncertainty due to weather variability. The present study aims at developing a weather year generation methodology (WYGM) for sizing a solar PV and WT power plant and hydrogen energy storage (SWHPP) for a year-round reliable electricity supply such that the uncertainty is efficiently identified so its effect can be minimized. The formulated WYGM named "SITY", which stands for speed-irradiance-temperature year. SITY has four major steps: global-sensitivity-analysis-based selection of parameters (GHI, wind speed, and ambient temperature), truevariability-and-real-sequence-based selection of block-size (equals to the temporal resolution), typical-to-extreme scenarios considerations in the generated formats ( i.e., average, most-frequent, worst, and best), and applying an all-parameters-atonce candidacy criterion (Euclidean distance of a 3D-space) for selecting the best representative data point. In particular, for generating SITY, of the most-frequent format, a new method has been developed, which matches the nature of the selected parameters, and it operates in a site-specific fashion. SITY has been applied for a selected site and was input to an adopted sizing algorithm. According to SITY, the uncertainty, due to weather, can reach up to +/- 3.01% and +/- 5.6% out of the required area and energy storage capacity, respectively, for a SWHPP. Also, the normalized-percentage MBE and RMSE and the index of agreement, for the purpose of evaluating the efficacy of SITY to capture the true variability and real sequence of the most influenced parameters, were obtained, of the all four formats, as follows (range): (-4.24)-(1.48)/0.9-9.67/0.939-0.999, (-14.34)-(2.22)/2.67-28.94/0.59-0.99, (-14.25)-(10.25)/5.83-17.03/0.890.98; for GHI, wind speed and temperature, respectively. In future, SITY would be implemented in a software generator to avoid the site-specific limitation of applicability.