A warm front approaching the region later tonight and pulling through the region on Tuesday will cause an increase in cloudiness. There could be a very isolated shower or thunderstorm, but the best lift appears to occur north and west of the region. Areas of fog are possible on Tuesday Morning.
On Wednesday, a lee side trough could trigger a few showers and thunderstorms. Confidence on the thunderstorms developing remains low. The model guidance has trended warmer from last week with regards to Wednesday and suggest 90 or better is possible at PHL. Some guidance even suggests mid 90s are possible. However, the lee side trough could throw cloud debris into the picture and even a few thunderstorms which could prevent 90 or greater high temperatures. In addition, the soil moisture remains abundant and this helps to offset some heating at the surface and this was likely one of the reasons many climate sites failed to reach 90 in our wet August. At this moment in September, we still have a damp ground along with a slightly lower sun angle. For now, I will raise the temperature to 91 degrees, although it could easily be one of those 89 degree days where we just fall short. Subsequent forecasts may have to adjust the temperature a bit more.
For Thursday, a strong cold front is going to pass through the region. Sun and clouds are possible before the arrival of showers and thunderstorms. Temperatures could rise well into the eighties and it will be humid. Given the setup, some severe weather is possible in addition to a threat for heavy rainfall. A large dome of high pressure builds in for the weekend. A refreshing and autumn like air mass is expected to settle in across the region. Low humidity and highs in the low to mid 70s are expected. Some locales outside of the urban corridor may not rise above 70 on Saturday. Lows could approach the upper 30s and lower 40s in the suburbs. There is a threat of frost, especially towards the Poconos.