Special 156-h East Coast Analog Run: 19 December 2012

If the 156-h forecast from the GFS 20121212/1200 model run is close to verifying, the most similar historical events indicate that from Binghamton to Albany, NY through interior New England would most likely have a white Christmas. Although timing of the system between the GFS and the consistent (as of late) European model during this period differ, there is support from the GEFS members that this threat is very credible. Fields between the top 15
analog means and the GFS forecast are similar...this is shown below in the 300-mb height, 500-mb height, 850-mb height, and PMSL field comparisons.

In addition, there is an excellent 850-mb u- component wind standardized anomaly signal (discussed in Stuart and Grumm 2006) from the top 15 analogs (shown below). That field in particular was found to be the most distinguishing characteristic between Northeast Heavy Snow Events and near misses (Gravelle 2011).

However, all the analog guidance evidence does not support a heavy-snow event. When the 850-mb temperatures from the top 15 analogs are compared to the GFS forecasts, they are (on average) about 3C cooler than the GFS forecast across the Northeast.

If upcoming model forecasts trend towards the colder analogs, it would suggest that heavy snow across a large portion of interior New England is a considerable threat. The mean COOP snowfall from these events has a large area with >6" of snow and there is a >12" of snowfall probability signal (>60%) with more than half the top 15 analogs. 

One of the more similar individual analogs to the forecast is from December 1986. In this event, the low-level thermal profiles were also similar (shown below) as temperatures range between 0 and -3C at 850 mb.

Although the heavy snowfall was not as widespread as in the colder analogs, snow in excess of a foot did occur in the higher elevations across NY, VT, and NH.

It is important to remember that the forecasts from the two global models mentioned above may change considerably since the event in question is a week away. However, by examining similar historical events, meteorologists can determine which fields (in this case the low-level temperature fields) may control the type and amount of sensible weather across the region. These fields (and their trends) should be focused on while interrogating model output.

Lastly, there were two sets of heavy-snow analogs within 10 days of each another: 2 and 11 January 1987...and...7 and 15 December 2003...if this large-scale pattern establishes itself, there is the possibility of multiple high-impact events across the Northeast.

The analog run that this blog post was written from is available here.

References:

Gravelle, C. M. (2011). Examining the reliability of the Northeast U.S. heavy snow conceptual model. Ph.D. Dissertation, Saint Louis University.

Stuart, N. A., and R. H. Grumm, 2006: Using wind anomalies to forecast East Coast winter storms. WAF, 21, 952–968.