Energy ejecting out of the southwest United States will move out to the northeast and spawn a weak area of low pressure in the mid Mississippi valley. The low will head towards the Ohio river and West Virginia initially, while strengthening gradually. Once it reaches this position, it will transfer its energy to a coastal low off the Delmarva. Meanwhile, the eastern flank of a banana high pressure will be located to our north and northwest, and low pressure which is now exiting our our this morning will be over the Canadian maritimes, as the Polar Vortex spins centered around Hudson Bay Canada. These three features will act to effectively block the initially low from gaining much more latitude, and force it to move to the coast.
There should be ample moisture available to the storm initially from the Gulf of Mexico, and then the Atlantic as the coastal low forms and strengthens. The cold source will be there in the form of high pressure to our north and northwest, and there will be at least some blocking present given the 3 features described above. This will result in some rather significant snowfall accumulations particularly north of the Mason Dixon line in the northern mid-Atlantic into southern New England, including the I-95 cities from Philadelphia to Boston, initially in the form of warm advection snows, then as a result of the coastal low taking shape. Right now, a general 6-12″ of snow looks likely, and this includes nearly all of the state of PA, central and northern NJ, southern NY state, and much of Massachusetts, Connecticut, and Rhode Island. This snow will be falling with temperatures primarily in the 20’s (and in some cases colder) in much of PA, northern NJ, and coastal New England on north, and therefore snow ratios will be higher than the 10:1 shown on most snow accumulation maps, probably in the 12-15:1 realm. South of the Mason Dixon line, there will be some mixing or a changeover, and this includes DC and Baltimore, as well as most of Delaware, particularly south of New Castle County, and South Jersey especially areas south of Atlantic City. I could see mixing go as far north as within a few miles of the PA turnpike, but I don’t think the rain/snow line gets much farther north than that. There is very close to universal model agreement in this scenario, somewhat of a rarity this season, with the exception of the Canadian model, although it’s ensembles are in agreement with the other models. Systems like these have the ability to overperform, especially on the front end, and that’s something we’ll have to watch for regarding QPF increases in the modeling over the next 48 hours and on radar once the storm forms late Saturday and Sunday. Snow should start from west to east around the time of the Superbowl (be aware it may very well be snowing after the game for most) and last through at least Monday afternoon, which is a relatively long duration event.
So given what happened with the last storm, you are probably asking, what can go wrong or right, depending on your perspective with regards to snow. The position of the Polar Vortex is key in this situation, and any deviation farther north or south will result in the initial low moving more north or south, and result in a warmer (more mixing and less snow south) or colder (more suppression and snows farther south, less north), respectively. That’s the one wildcard, but right now, given the rather good model agreement, I don’t expect things to change significantly. And could the storm be a miss like the last one? That’s VERY unlikely, as this storm will actually be formed with a large precipitation shield BEFORE it reaches our area. The last storm was dependent solely on redevelopment of a clipper low which had a paltry amount of snow before the coastal low rapidly intensified, and in our case for the northern mid-Atlantic, too far east to really affect us.
Beyond this storm, I see no significant warm ups in site. Weak Modoki El Nino winters are almost always back loaded, with the greatest degree of cold and snow coming in March and February, and in some cases into early April. Given this fact, and the SST profiles which continue to be very warm off the west coast and in the Gulf of Alaska, similar to last year, and additionally those in the northern Atlantic, which remain favorable for blocking, as well as the inevitable weakening of the -QBO in the next few weeks, I see winter extending well into March if not early April. So there is plenty more snow for those who love it. For those who love Spring, I think they’re disappointed much like last year, especially if they were hoping for early warmth.
More on the late weekend storm as warranted.