The above is the 12z EURO model run at the 500 mb level. By looking at the vort maps, we are able to see that the EURO closed off the H5 vort over central North Carolina. This model is the only model to close off H5 this early which is why it is taking a storm track right along the coast. Heights rise ahead of it and the storm tightens / strengthens much quicker. The region starts as snow, then changes to rain, to end as snow.
In comparison, the 12z GGEM (Canadian) model does not close off H5 at the time the EURO does, but the energy at the base of the trough is much stronger which still raises heights off our coast to promote a storm track tucked in west from the benchmark. In fact, the GGEM really explodes this storm system and brings crazy amounts of both snow and rain to the area. Of the three global's, the GGEM is the strongest one.
The GFS also does not close of H5 as early as the EURO model. However, this model has struggled greatly with the synoptics of this storm because it has been shearing energy from the west side of the trough which strings out the low level center a bit. The mid-levels fall apart and the surface maps begin to make no sense with a 980 mb low off the coast with not much precip. to show for it. The GFS has made strides to the other models, but at this point, I think it should be disregarded until it straightens itself out. Heights are also flatter along the east coast compared to the GGEM/EURO which is why the GFS tracks this storm right on or just east of the benchmark.
A common theme you will find in all of these models is that it does warm temperatures up enough to change snow to rain for some locations, including NYC Metro. This is where the forecast becomes tricky.
Here is another look at the 12z GFS model. One thing you will notice is that there are two areas of High Pressure surrounding the northwest and southwest quadrants of our coastal storm. The first one is north of Maine, which could help provide us with cold air to prevent snow from changing to rain. The second is along the Gulf coast. The third piece we should pay attention to is the potent clipper in the Great Lakes region. One of the many things I am keeping an eye on is if those two anomalies are providing too much subsidence for our coastal storm to really deepen and bring moderate to heavy banding over our area. Vertical velocity at H7 (frontogenesis) is not going to be impressive if those two pieces are there to disrupt the evolution of our coastal storm and preventing it from amplifying. This could be one of the reasons why the GFS has a funky look to it and I definitely think it should be monitored.
Another important factor to look at is to see where the 700 mb and the 850 mb low's close off. The Canadian model, for example, vertically stacks each of these low's inside the BM which is another reason why it outputs such an extreme scenario.
For example,
12z GGEM 700 mb
12z GGEM 850 mb
One other factor I am considering when trying to forecast this storm is the seasonal trend. We are now in mid-February and have a good idea of how the storms this season have behaved. None of them had a storm track inside of the benchmark. Most of them remain south and east of the benchmark and brought the heaviest precip. amounts along I-95 and points east. I'm only mentioning this because the GFS / NAM models are not sold on the idea of having a storm track hugging the coast. I can see why with the lack of blocking (-NAO) and areas of confluence to the west of the storm why those tracks could be justified.
How all these factors evolve will determine how this storm plays out along the NYC Metro area. Consistency is there that a long duration event is likely to begin early Thursday morning and continue into Friday morning, possibly a 24-hour + storm. It is certainly possible Blizzard criteria is met and watches / warnings are issued for the area, but that will not be realized until the factors I mentioned above are known.
Here is an example on the extreme side of what winds at the surface could look like for our area. This is from the latest 18z NAM:
With all that being said, here is my 1st call snow map with this storm system likely to be changed again tomorrow. But I wanted to put this out there so everyone can get an idea of how I view this storm panning out. I do think the GGEM/EURO are a little too far west right now. While they have been consistent, we cannot ignore the consistency of the GFS/NAM either. The UKIE was also a little more east today at 12z compared to its 00z run. A lot depends on when exactly H5 closes off. I think it will happen along the coast of NC or SE VA, not interior Mid-Atlantic like the EURO shows.
My current thinking feels the models tonight into tomorrow will begin a trend with this storm system a little further east. I think a track right along the benchmark is fair to say at this time because of some of the factors I mentioned throughout this blog post. If the western most track comes to fruition, the heaviest totals will have to be pushed further west and lower amounts will occur along the immediate coast due to mixing. At this time, I do not see that scenario panning out but this is a high volatility forecast.
Temperatures Thursday morning, the time the storm is expected to start, are only in the low to mid teens across much of the area. Couple that with a possible High to the north and evaporational cooling from our current snow pack, I think models also have a good chance of trending colder with this storm once the dynamics are realized. There is a lot to digest here. Extremely complex set-up.
Thanks for reading,
Francesco Paparatto
*Please visit the www.njstrongweatherforum.com forum for continuous discussions about this impending storm*
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