The ingredients are coming together for a major storm to impact much of the east coast on the busiest travel day of the year. In terms of the general overview, after dry weather Tuesday and Tuesday evening, we will see a cold rain moving in by Wednesday morning and lasting through the day. The big wildcard is the potential for the rain to mix with and change to snow later Wednesday into Wednesday night. This will be a very complex storm system, and since the storm is a couple of days away, a lot of the fine details will change quite a bit.
One difficult part of the forecast is that one of the main ingredients of the storm is going to travel about 4,000 miles before it gets here. A piece of energy in atmosphere will move from near British Columbia down through the Rockies and into the Gulf of Mexico by Tuesday night. 
This energy will combine with an area of low pressure developing along the remnants of a cold front in the Gulf of Mexico.
What the storm does after this point will dictate the amount of precipitation and how much of that could fall as snow. We have looked at quite a few computer models, each with its own subtle (or major) differences. These differences change with each new computer model run, and the overall track of the storm varies widely. Keep in mind that a change in storm track of just 50 to 100 miles will mean a great deal of difference regarding precipitation type and amounts.
If the storm moves right against the coast (or slightly inland), it will be mainly rain for much of our viewing area for the majority of the event. The storm will finish with cold air, but that cold air will arrive after most of the precipitation has ended.
If the storm tracks a little off the coast, we will see rain for the first half of Wednesday, but as colder air spills in during the afternoon, rain will begin to mix with snow for areas well west of I-95, and this transition zone will move eastward during the evening. The period of potential snowfall will be longer with this storm track, especially for the northwestern half of the state. If this particular track shifts a little eastward, this means the transition zone will get closer to the coast earlier.
A couple of our computer models have been hinting at a storm track that pushes the bulk of the storm too far east to impact us too much. This would produce the least amount of rainfall, and the chance of any snow would be low.
As of now, it looks like something between track # 1 and track # 2 may materialize. This will mean a wet first half of Wednesday with rainfall amounts over one inch possible. The rain will mix with snow well west of I-95 in the afternoon, and that mix will push into the metro towards evening and towards the coast overnight.
Temperatures for the start of Wednesday will be in the upper 30s and lower 40s. These temperatures will then fall as the day progresses. Ground surface temperatures will remain above freezing until Wednesday night, when cold air and rainfall/snowfall causes the ground to reach 32°. Any snowfall accumulation that does occur will be slow to start, and affect grassy surfaces first.
Precipitation from this storm will exit our area by Thursday morning. A disturbance later in the day may produce a rain shower or some flurries, but should have no impact on area travel. Our area will see dry weather on Friday, followed by warming temperatures next weekend.
Once the storm leaves our area, the storm track will be crucial for the northeastern United States as well, as major metropolitan areas like Philadelphia, New York and Boston will be affected.
As mentioned before, due to the complexity of this storm, a lot of the details will change over the next couple of days. Please continue to monitor our updated forecasts.
