The ECMWF is printing a potentially dicey situation for the East Coast in a possible severe weather event scenario. What we have here is hour 168 of today's 12z ECMWF. It is considered long range, so don't get too hooked on it.
This storm system looks to be a pretty well organized system, with a warm sector in front of it, pulling up warm, unstable air from the South as shown by the brighter colors being pulled towards the center of the storm. Another side of the storm is the following cold air, shown by the cooler colors in the Great Lakes. As shown in the spring and summer, severe thunderstorms do happen when opposing air masses collide. However, luckily, it is not spring just yet.
Of more interest is the RH values along the East Coast. The way the RH values are positioned in a diagonal line of sorts along the Coast makes me concerned that the ECMWF is looking at a squall line forming. This really would not surprise me, with the warm sector being pulled out ahead of the storm system. The good news is that these RH values are between 60% and 90%, meaning that confidence in this possible squall line is low. The ECMWF does not publicly distribute precipitation charts, so these RH charts are the next best thing.
An area of 90%+ RH values does exist to the east of Pennsylvania. That does appear to be a rain event, judging by the 850mb temperatures and the proximity to the storms center. Again using proximity, it does not look to be a huge severe weather event, but some storms are possible offshore, as this blob of higher RH may be the warm front pulling up the warm air ahead of the storm.
Offshore may be a different story. The warm sector out ahead of the possible storms combined with maximum wind speeds of 60 knots just offshore the Northeast region tells me that waterspouts are not out of the question. Waterspouts are basically tornadoes on water, but with a lot less strength but still with damage potential. It is somewhat rare to have waterspouts hit land after forming at sea, and even rarer to have those waterspouts continue on land.
All in all, this doesn't look like a huge severe weather event if it does happen. The ECMWF does appear to be hinting at a possible squall line, which would provide some concerns, but again, nothing too major.