PHILADELPHIA - With Tuesday marking the official start of fall, the final weekend of summer will be quite pleasant and cool.Saturday kicked off the cooldown with low temperatures in the upper 40s and a high of just 65 degrees.Sunday looks almost identical with a high of 64 degrees, and both days are expected to bring plenty of sunshine.Monday will continue the fall-like trend, but by Wednesday temperatures across the Delaware Valley will be heating back up.Wednesday and Thursday are both forecasted to bring highs of 80 degrees.So far, the seven-day forecast doesn't include any major rain threats.AdvertisementFor the latest forecasts and conditions, download the FOX 29 Weather Authority app.___For the latest local news, sports and weather,.