Wednesday, April 18, 2012

Late Season Snow for Northeast Possible Next Week
The latest GFS and ECMWF are hinting at a late season snowfall for the Northeast next week, as temperatures look to plunge below freezing and a massive storm system strengthens in the presence of the Atlantic Ocean. In this discussion, we will review things pointing towards the snowfall as well as caveats to the potential snowfall.

A caveat of this potential snowfall includes a crashing PNA index. The Pacific North American pattern, commonly referred to as the PNA, looks to be moving towards a negative phase around the time of the storm system. When the PNA is in a negative phase, a ridge is pressed into the Southeast and diverts storms away from the Northeast. Snowfall producing storms are favored in positive PNA situations. If this PNA forecast were to verify (which I am not completely sold on yet), the system would likely be forced away.

Something I would watch for is the NAO to help this storm. Seeing as it is being forecast into a negative phase, the North Atlantic Oscillation (NAO) would position variables to become conductive for a snowfall in the Northeast. I advise you not to totally take the NAO and run, because if you see the correlation with observations in the 14 day forecast on the bottom, there is only a 12% verification score in the past 4 months or so. Notice the glitch just before January 1. This likely battered down the score, so I would place the verification around 30%- still not very good.

Other Positives
•ECMWF/GFS model agreement is reassuring.
•NAO appears favorable for some light snow.

Other Caveats
•PNA must be considered.
•System remains 6-7 days out.