A Complex Storm Coming On Tuesday...

The models are finally starting to come into some agreement on what is going to be a very complex and difficult situation to forecast in the Mid-Atlantic and Northeast come Tuesday. This is Student Meteorologist Kyle Elliott, and I want to start off by apologizing about not posting a forecast on this storm in the last two days. The reason I had for not doing this was to let the models sort themselves out somewhat as the Euro, NAM, and GFS were worlds apart during the last couple of days. Also, this situation is still going to be very difficult to forecast, and I frankly wasn't quite sure which was I was leaning the last few days as there are many small factors on the table that will have gigantic implications as to the outcome of this storm. So, let me make some points here this morning and let you know how I think this will all unfold:

1) What we have here is yet another two-pronged system. First, there will be a storm system in the south that eventually ends up off Cape Hatteras once again. The problem this time, though, is that there will be another storm tearing up into the Lakes...remaining separate from the coastal storm. At the same time, A cold high pressure system over the Northeast will, instead of locking in, drift out over the Canadian Maritimes. This will allow for a southeasterly flow aloft to sweep through the Mid-Atlantic States in particular come Tuesday afternoon and evening. Now, what this means is that any precipitation which starts off as snow in PA and MD would eventually turn to sleet and freezing rain as temperatures aloft go above freezing while bitterly cold air remains locked in at the surface. Ultimately, in a scenario like this, precipitation would go over to rain at the end...but just how soon that would happen will have huge implications on the severity of the ice storm in the Piedmont and Ridge-and-Valley regions.

2) Now, let me describe how the models vary. I'll start off first with the NAM. The NAM basically is the best-case scenario for those not looking for much of anything but rain from this storm. It has one storm center way west and north going through the central and western Great Lakes...while keeping the storm on the coast weaker and farther east than the GFS. This model, especially the 12z run, warms things up aloft and at the surface very quickly...while keeping the heaviest precipitation confined to the I-95 corridor eastward, making it a rainstorm. On the west side, it's an all-snow event into the Lakes on the NAM...while in the middle, there is this harmless 200-mile wide gap with nothing happening at all but partly cloudy skies and mild temperatures. Honestly, I highly doubt this scenario as the NAM has been switching back and forth between ideas on it's like 5 or 6 runs. It's had a great track record in the short term with the last two major storms...but it's long-term guidance has been iffy at best. Therefore, it just doesn't look like them model of choice to me. The Euro, on the other hand, has pretty much the same scenario but looked much colder when I glanced at the 00z run. It kept the coastal storm way east and the Lakes storm very weak, allowing for much colder temperatures to be found throughout the Piedmont and coastal plain. I didn't get chance to look at precipitation, but my guess is that the Euro was too far east and really didn't do much to anybody. The model of choice right now, in my opinion, is the GFS. It has the coastal storm doing much what the past two storms have done...while taking a middle-of-the-road solution between the Euro and NAM on the lakes storm. The GFS shows one heck of an ice storm for areas of northern MD through PA and far southeastern NY. It warms things up aloft, but temperatures are slow to recover at the surface as heavy precipitation abounds during the coldest part of the day on Tuesday morning. This makes most sense to me as temperatures, especially this time of year, are slow to recover at the surface in Cold Air Damming situations like we have here. My best guess now is that areas of MD and PA start off as a brief period of 1-3" inches of snow at best...then transition quickly over to an ice storm which could wreak havoc on the east side of the mountains. Just how heavy the precipitation is and how far west it really gets will have huge implications as to the degree of the icing event...but I would expect a west trend on the NAM and Euro as Tuesday draws nearer. It's still a very complex situation, though, and one which I'm a little shaky on myself at the moment with a low-confidence forecast to be honest.

3) My third and final point is two-fold. First, this is NOT going to be as big of storm as the last two. There could be a significant icing event in the Mid-Atlantic, but the snow aspect of this storm will be minimal as coastal areas will warm up quickly and should not have to deal with much more than rain after a possible period of snow at the onset. Second, what I'm beginning to grow more concerned about is the storm trailing this one. The 6z NAM/DGEX suite showed a major storm coming up around hour 102-114 throughout the Mid-Atlantic and Northeast. This kind of reminds me of the time frame of December 1st-5th, 2009, in that one storm gave mostly rain and ice to the Mid-Atlantic followed up by a sneaky 3-6" snowstorm on the 5th of December, 2009. The difference is that this first storm will be much colder at the surface than the storm on the 1st of December, 2009, and the second possible storm on Wednesday/Thursday may not have enough cold air to work with by that time to produce much more than a rain/snow mixture in the Mid-Atlantic area. On the other hand, this scenario is only shown by the NAM and GFS...the Euro holds off and instead blows up yet another monster storm between hours 144 and 168. The GFS and DGEX showed this storm yesterday being mainly a clipper event, only to totally lose it on the runs today. My point is this: there is much confusion on the models as to the pattern and how it's going to come about over the next week, and it will be a wait-and-see situation where last-minute forecasts will turn out to be the best.

Well, that's all I want to say for now, so hope ya'll have a great day and I'll post again this evening as new guidance comes in. This is Student Meteorologist Kyle Elliott reporting for the AKStormtracker Forecasting Center!