Tuesday 9 a.m.
Yes, the GFS operational run from yesterday afternoon included a forecast map for the afternoon of Oct. 10 that suggested heavy wet snow would be falling over the higher elevations of central and northern Pennsylvania. That map is below. The output from the same model run 12 hours later shows no such thing... just a Great Lakes low pressure area causing showers with fairly mild temperatures. That map is below the snowy version.
At this point, we cannot put much faith in either idea.
In the shorter range, southwest winds are sponsoring a warmup in the Northeast from today into tomorrow. A cold front will then move though to cause some showers and in places a thunderstorm... followed by cooler air. The front will stall in Virginia or Norrth Carolina, and a low pressure area forming along the front can then bring rain to the Middle Atlantic states on Friday. The video has more.
The reason for this is a growing and then stalling storm aloft. This map shows the predicted circulation around the storm on Wednesday evening, showing how the moisture could keep going round and round until the storm leaves.
This mornng, showers were moving across the lower Great Lakes region. A band of thunderstorms developed near Chicago before 6:30 a.m. CT and reached the southwest Michigan shoreline an hour later (8:30 a.m. ET). The following maps show the shower zone and Chicago area lightning.
The tropics have been more active recently. This map shows various entities that area being tracked and analyzed. Hurricane Gonzalo stands out clearly.
A couple of days ago, the storm entering the East had a stronger circulation than it does now. Here is the pressure analysis from earlier this morning. Several minor disturbance can be seen, and trough lines representing those have been sketched on the map. Note that there is little difference in temperature from western Pennsylvania to Wisconsin.
The rain band is only 100-200 miles wide, but it is moving slowly. This map shows its location at 10 a.m. today. Once the main rain band passes, it won't be quite as warm as it was when the rain started. However, by mid-October standard, it will still be mild.
On some days, there are so many "little things" that it is difficult to identify the players. Today, we see two systems dominating: the low pressure area on the left (west) and the high pressure area to the right (east). The cold front associated with the low pressure area is helping to support bands of rain.