Monday, December 30, 2013

January 1-3 Significant Winter Storm - Part II (Northeast)

This post will address the potentially significant snowstorm that is aiming for the Northeast. If you would like to see Part I, where I address the potentially significant snowfall in the Midwest and Great Lakes from this storm, please click here.

Tropical Tidbits
Valid January 2nd, morning.
The mean sea level pressure from the GFS model shows how this potentially significant snowstorm may evolve. We see the super-charged semi-clipper that was elaborated on in Part I over Indiana, but then we see another low pressure system skirting to the east of high pressure based in Georgia. It is these two bodies of low pressure that we are monitoring closely for what they will do. Current projections include phasing (combining) of the two systems, but the question is: When will they phase? In this case, timing is key.

Model guidance remains at least slightly uncertain with when these two systems will phase into one, stronger low pressure system. It is believed that the earlier the systems phase, the more snow they can spread on to more residents of the Northeast. Similarly, the later the systems phase, the less snow they provide to fewer residents.

Tropical Tidbits
Valid January 2nd, afternoon.
Roughly 12 hours after the first image in this post, the GFS model has the two systems interacting. Originally, these two systems were at 1010 millibars just three hours before this image you see above. Now, with the low pressure system offshore the Northeast stronger than the one just south of Pennsylvania, it is apparent that the clipper system will be transferring its energy east to the system offshore New Jersey. Just a handful of hours later, the system has phased into a sub-1000mb system. However, it is further offshore than many in the Northeast would like, leading to less snow.

The GFS isn't the only solution in the mix, however.

The ECMWF is slower with this system, having it phase completely on the morning of January 3rd. Because timing is key with when these two systems will phase, it is apparent that this timing difference between the ECMWF and GFS is a significant factor in each guidance system's solution. The ECMWF has this system phase earlier and become stronger than the GFS, with an added bonus of keeping the system closer to land than the GFS. The precipitation and MSLP image above from the ECMWF, again valid on the morning of January 3rd, shows a 978 millibar storm system due east of New Jersey, spreading intense snowfall across Pennsylvania, New York, Vermont, New Hampshire and into Maine. Even coastal regions to the south of NY, VT and NH get in on some snowy weather. The snowfall image from the ECMWF below paints the full picture:

Also worth noting is that the ECMWF Ensemble Prediction System (EPS) is on board with the earlier phasing.

So what do I think will happen?
I'm thinking we do see something along the lines of the ECMWF verify. I do not believe we see the huge ~24" totals (models have a tendency this winter to back off of big precipitation forecasts just prior to an event), though significant snowfall is certainly within the realm of possibility, even likelihood. I feel we see a swath of heavy snow ("heavy snow" meaning 8"+) stretching from New York/Pennsylvania out to Maine in very similar fashion to what the ECMWF portrays above. I would also monitor future model runs to keep an eye on that southern cutoff of snow totals for coastal regions, as I feel those areas will have to go into the event with a 'now-casting' mindset.


1 comment:

Anonymous said...

Andrew. Great site. I'm new here so apologies for this basic question, but when do you expect to update the discussion |models regarding the upcoming north east winter event. Thanks