Storm Recap – Why So Much Snow?

The storm was only a 1000 mb low once it was off of Long Island and if you look at the 500 mb trough, it really was nothing all that special in regards to a big trough. The key to the heavy snow was a couple of things.

  1. The arctic airmass had come in the day before and settled in over the Northeast. As the storm was starting, the arctic front was from near Baltimore into western PA. During the afternoon, the arctic front moved northwest into New Jersey and Maryland, changing the precip to sleet and rain in some areas. While the front really never moved all that north, the airmass to the north the front setup an area for high ratio snows to occur, especially from northern PA into Vermont and New Hampshire.
  2. We also had tremendous amounts of liquid over an 1.00″ being thrown well into the cold air which one would not think would happen given the trough size. The QPF for such a small storm was amazing to me, almost reminded me of a convective complex.
  3. Speaking of convection, the storm really never had thunderstorms that moved into the cold air. The snow will driven entirely from the low level jet transporting high moisture content air into an arctic airmass, something you don’t se every often.
  4. The forcing at the 850 mb level (5000ft) and the 700mb level (9000ft) setup and zone of forcing by evening from northern PA into NY as you can see on the maps below. Also notice the 850 mb winds over 50 kt blowing northwest into the area of convergence so in essence you had southwest winds at 500mb and southeast winds at 850 mb setting up an area of convergence.
  5. The are key point was the models. The operational models did a horrible job in regards to snowfall. Even the mesoscale models did a horrible job including the HRRR. Non of them picked up on the extent of the heavy snow and the heavy snow banding that occurred from central PA into NY. The only two models that were even close was the ICON and GFS-PARA. They seem to hint better at the heaviest snow areas.
  6. On my snow map that I issues, my errors were the snow band not far enough north into New England and New York and obviously the amount of snow which I don’t think anyone predicted. Also the mix areas from western Maryland to New York city was more extensive, but made sense given the strength of the 850 mb winds and the NW position of the heavy snow band.

As always lessons learned for the next storm. On the maps below, notice the forcing areas across PA and NY which line up with the heavy snow bands.



Great stuff Henry. Thanks for all of the maps and charts. Now, I just need someone to help me read them correctly. Especially the 850, 750 and frontogenesis maps:))

Weather Madness

The top left two maps are the two important ones. Notice the area across northern PA into NY. That is the forcing where the snow band setup along.


Fascinating, as Spock would say. Down here just west of Baltimore, my at-home barometer never dropped so quickly or went so low – and did not really start dropping fast until after we had the sleet/rain changeover. I knew something unusual was up.


Hi Henry.. thanks for all you do.. just wanted let you know we got 8 “ here on the island.. great storm.. we don’t usually see snow here this early. Kimberly from swans island maine