A low pressure system is expected to form over the Gulf of Mexico Saturday afternoon just off the coast of Florida. From here the low will ride the eastern seaboard up the coast. This is what the models agree on. Where they differ is on the exact track of the low once it reaches the northeast. The image below is of the NAM model predicting what this low may look like on Monday morning. The NAM has the low the deepest of any of the models at 980mb and almost directly over central New Jersey. I have done my best job to highlight the past path and future path of the low as depicted by the NAM in orange. As you can see, the NAM projects the low to continue heading toward the northwest into western New York throughout Monday. The NAM model only goes out 84 hours so it is unclear where this model may take the low after this but if the other models are any indication it will most likely begin to head northward. The other thing of note here are the wind speeds, reaching at least 20 knots and in some areas 30 knots plus. These wind speeds coupled with the snow that would be falling could very well create for blizzard like conditions in western New York and parts of northeast Pennsylvania.

The GFS model on the other hand does not depict as strong of winds but the winds still could be quite gusty under this scenario, shown below. The GFS leaves the low a little farther out to sea instead being located over the New York City area on Monday morning as a 988 mb low, which is not nearly as intense as the NAM predicted and thus why the winds are weaker. From here the low is modeled to move toward the north northwest into northern New York before retrograding into Ontario and moving north.
The ECMWF track, which I show below on a simple U.S. map, has about the same position over central New Jersey as the NAM model did for Monday morning but the intensity of the low only ever reaches 984 mb and is only 988 mb at this point on Monday morning. The track from here is very interesting as it progresses a little more northerly than the NAM track did putting it on the eastern shore area of Lake Ontario before it retrogrades to almost the opposite shore of Lake Ontario and then begins to head northward.

Despite the track differences, enough cold air will exist to create snow on the western side of the low. Below are images from the NAM showing the 1000-500 mb thickness near the onset of snowfall and then again on Monday evening when the storm would probably start to move northward after retrograding some. It is of note here that the GFS depicts a very similar looking scenario but has less wrapping of the cold air occurring around the south end of the low and less wrapping of the warm air occurring north of the low. This is most likely due to the GFS predicting a less intense low pressure. The line to note in these images is the 540 line which typically depicts the rain/snow line in these storms though in late season storms, snow can occur at thicknesses of 5460 or less. So areas in blue would be cold enough for snow and maybe even the lightest first shade of green.





Now this does not mean just because an area is below the 540 or 546 thickness threshold it will snow, as moisture and cold temperatures at the surface still need to be present. There will be plenty of moisture with this system as shown by the HPC’s image below showing precipitation over the next five days. Many areas across the northeast will pick up at least two inches of precipitation with some areas seeing in excess of four inches.

The cold temperatures will be the tricky part of the forecast and something that will need to be monitored as the event gets closer. Some areas are for sure cold enough for snow at the surface and other areas will be right around the freezing mark with what could play out as interesting temperature profiles aloft. The one threat that has not been mentioned by anyone yet with this storm is freezing rain. At this time it does not appear this will be a big freezing rain maker but if the NAM is right and the low deepens more, wrap around warm air advection could allow profiles to warm enough aloft to lead to some freezing rain in areas north of the low.
Below are the current predicted snowfall depths from the NAM (top) and GFS (bottom). The GFS image is from 12 hours after the NAM image and therefore the NAM may actually have more snowfall falling than is depicted in this image. As you can see the NAM is predicting more snowfall than the GFS but both of these models have come into some agreement on a general area of snowfall from the mountains of West Virginia northward into western New York and Ontario.

The ECMWF on the other hand appears to give a solution more similar to the GFS with a little more snow expected for parts of northern New York. It will certainly be interesting to see how this plays out but the threats of heavy rain, wind, snow, and maybe some freezing rain are apparent. Below is a map of what I am thinking could be the threats as far as precipitation type goes.
The green areas should be ready for rain, of which some could be locally heavy in excess of four inches. The orange area is the mixed bag area. Here we could see all rain, all snow, or something in between. These are the areas that really need to monitor the future forecasts on this storm to see if they need to prepare for any snow or freezing precipitation. Areas particularly in danger could be northern New York, especially the Adirondacks, and parts of the mountains in southern New York and Pennsylvania. If the low does not deepen as much these areas could see more snowfall as less warm air wraps around the low. The area that should see all snow is highlighted in blue with dark blue depicting an area that is at the greatest risk right now. This greatest risk area could see snowfall amounts in excess of six inches which could cause power outages due to the fact that many trees have their leaves or have started getting their leaves. This heavy snow coupled with blustery winds could mean many trees and power lines would be down across this area. Definitely pay close attention to the developments on this storm throughout the weekend as the forecasts for this storm are anything but set in stone.