Currently: A warm front extended from near Green Bay to near Philadelphia. This warm front triggered off some light rain over Pennsylvania, but that rain is now moving into a drier air mass and losing most of its punch.
Tonight: Temperatures probably will only fall a few degrees from where they are now, since this warm front will approach and clear the area. I will be going a few degrees warmer than all temperature guidance. As far as rain chances, a few sprinkles are possible from about I 84 on north, where there is slightly better forcing, until about sunset, otherwise I will not include rain in the forecast.
Tomorrow: Much warmer, due to being south of the warm front. The temperature spread will be fairly common for what we see during an April afternoon; generally upper 60s to low 70s. There could be some mid 70s along the I 91 corridor, and along the immediate SE coast, temperatures may not make it out of the low 60s.
Tomorrow Night/Sat: The NAM and the GFS are 15 to 20 degrees different regarding Saturday afternoon's temperatures, and this is because the NAM blasts the back door cold front through the area Saturday around midday, while the GFS waits until Saturday night. The NAM does have a bias of bringing these things through too fast. Additionally, climatology would make sense for this thing to go through more at night, rather than during the day. However, there is also a very strong high pressure system to the north. For now, I feel the conservative route is preferred, that is to say, almost a straight split of guidance, with a VERY slight lean toward the GFS. This yields temperatures generally 60 to 65 across the state. Suffice it to say, this is a VERY low confidence forecast.
Long Term (Sunday and beyond): As this frontal boundary goes nearly stationary and wobbles around near the state, waves of low pressure will develop and move along the frontal boundary. Areas of rain, some of it heavy, will accompany the low pressure zones. I will go about 5 to 7 degrees cooler than the GFS guidance north of the Merritt for Sunday and a degree or two lower than that guidance along the south coast, which yields a chilly and rainy day Sunday, with temperatures in the 40s across the state. It should be noted that the long range NAM guidance is an all-out ice storm for the state. For now, that guidance is being ignored, since it has no support, but it is interesting to keep in mind.
On Monday, the front begins heading back north. It is unclear at this time whether or not the front will clear the region. However, the GFS loves to blast these fronts north much further than reality at this range. I will already be going about 5 degrees below GFS temperatures throughout the state on Monday, which yields statewide temperatures within a few degrees of 60, but that might not be cold enough. Rain will dominate the weather picture on Monday. In fact, even a few imbedded thunderstorms are possible Monday morning and early afternoon. Rain begins to taper off later in the day.
Cool high pressure builds in on Tuesday at the surface, while an upper level low swings through the region. Soundings show very low convective temperatures and very cold air aloft. Models often overestimate high temperatures in a set up like this. Therefore, I will once again go a solid 5 degrees lower than temperature guidance, and cap highs in the upper 40s throughout the state. In addition, as that upper level disturbance swings through, some light showers will be triggered during Tuesday afternoon. With such low temperatures aloft, it would not surprise me if some sleet pellets or snowflakes mixed in for a time. When the upper air is very cold, this can sometimes happen with surface temperatures well above freezing.
For Wednesday and Thursday, a general moderating trend looks to be in store. However, convective temperatures still remain low, so a lot of cloud cover should be generated each afternoon, and temperatures should still turn out a few degrees below guidance. Additionally, another system in the flow buzzes through on Thursday, producing some light rain during the day. As for temperatures, expect highs to range from 50 to 55 on Wednesday and a few degrees warmer on Thursday. Wednesday morning should see widespread subfreezing temperatures north of the Merritt Parkway.
Looking into the longer range, a generally stormy pattern looks to continue, with temperatures riding a roller coaster of sorts, but generally averaging out below normal. There are no hints of any major pattern changes on the horizon.
Now, let's take a look at Sunday's rain storm and how it evolves into Monday on the modeling. This map is valid Sunday midday. At this hour, the state is entirely in the cold sector, so expect chilly temperatures. While there is no really heavy precipitation on that map, you can see lots of light rain, making for a raw, dreary, chilly Sunday.