After reviewing over some more possibilities today, I made some slight revisions to my scenario map from yesterday, though I’m not planning on making much more changes unless a significant change happens in the pattern forecast. The models may still be all over the place, some of them suppressed and others further north, but the real hint that helps us determine where the storm ends is the pattern.
The main factor that caused all of the storms this year to take a south track was the polar vortex, or the PV. So far this year, it’s been quite strong, which blocked the storms from going too far north, and the storms that did try and move north had to transfer their energy to a secondary low, being a coastal storm. The latest forecasts show that this blocking pattern should weaken some by the time that this storm arrives, and with the past few storms having taken a track supportive of widespread snow in the Mid Atlantic with a strong PV, a weaker PV will allow this storm to move further north. Another factor that may be an issue for this storm is the lack of a 50/50 low (a low pressure located near 50N, 50W), which is an important factor in winter storms.
Another problem that we have is the lack of any real cold air. The storm should not have too much cold air at first, and there isn’t a high pressure to our north to lock in the cold air. With the primary storm also being able to travel further north due to the weakened PV, more warm air will be drawn into the area. This set up would bring enough warm air that the major cities along Interstate 95 change over to a wintry mix and/or rain. The wintry mix could even end up extending as far inland as central Pennsylvania, most of Massachusetts and southern Maine.
Below is my current scenario map for this storm. Unless there are any major changes, I am planning to stay with this discussion until Saturday, when I should probably make a more detailed map, with accumulation ranges and areas where rain, mixing and snow are possible. Here are also my current expectations for each city:
Washington DC: May start out with a brief mix, but otherwise rain.
Philadelphia: Some mixing is possible at the start, followed by a changeover to rain.
New York City: Some wet snow to start, some accumulations possible, followed by a changeover to mix/rain.
Boston: Snow to start, followed by some mixing later on. Rain could mix from Boston and further south.