As we wind down the fall season(astronomical winter begins Saturday at 12:11pm EST) these next few days shall feel anything BUT Fall!
Mind you that the average high(30-year average from 1981-2010)for Philadelphia is 43 degrees while the average low is 29; this weekend we'll have highs in the middle 60s and lower 70s with lows just into the 50s(the overnight lows will be HIGHER than the average daytime high!). Now why is this happening? It's all thanks to a potent upper-level low situated across the Southeastern United States; basically it divides cold air in the Upper Midwest and the warm and humid air across the South and Northeast. There is of course, a frontal boundary dividing the two air masses and along it is copious amounts of rain(2-3" of rain with higher amounts) that will affect the Midwest over the weekend. There is also a severe weather outbreak possible across the Mississippi River and Tennessee River Valleys come Sunday as that upper level low pushes east it will help enhance dynamics; with enough uplift along a warm and humid air mass you can get strong to severe thunderstorms to develop(also with some more support from a jet streak, or ribbon of strong winds within the jet stream) that can also spin up tornadoes. Nothing like that will occur here luckily as the upper level low will then track north and pass us by eventually to the north come Monday, BUT we will still have the potential for some heavy rains in excess of 1" come Sunday afternoon and leading into Monday morning.
Before the rains come we will have a mostly cloudy day for Saturday(that means a few breaks of sunshine are possible) and an overcast Sunday with rain pushing in by the late afternoon(so the Eagles/Bears game will be wet, but at least mild!). With this in mind there are TWO high temperature records to keep track of for this weekend; Saturday's record high is a long-standing one set back in 1895(shockingly, records go back to 1872)with 66 degrees; we are going to come close to this number as depending on how much sunshine we get and how good of a southwest wind can really surge that warm air northward. I feel that middle 60s are manageable, but the record high for Sunday is 64 set back in 1998 which I feel very confident shall fall with an expected high at or above 70 before the rain arrives!
If you'd like to see how the forecast pans out you can check out www.scottderekwx.com/forecast.html for the forecast (it's free as I would NEVER charge money for something I love doing!).