SEVERE combination of critical meteorological and hydrological CONDITIONS that rare REASONABLY possible in the REGION.It is computed by using the Probable Maximum Storm (PMS) which is an estimate of the physical upper limit to storm rainfall over the catchment.Standard Project Flood (SPF):This is the flood resulting from the most sever combination of meteorological and hydrological conditions considered reasonably characteristic of the region.The SPF is computed from the Standard Project Storm (SPS) over the watershed considered and may be taken as the largest storm observed in the region of the watershed.It is not maximized for the most critical atmospheric conditions but it may be transposed from an ADJACENT region to the watershed under consideration.