Tuesday, November 8, 2011

October 29-30 Snowstorm Ranked a NESIS Category 1

The Northeast Snowfall Impact Scale (NESIS) is a recently developed metric for assessing the geographical impact of large East Coast snowstorms.  Statistically, it is computed by examining the correlation between population density and snow footprint (areal coverage, depth of snow).  Widespread snowstorms of significance in the Northeast Corridor are assigned a NESIS score, and ranked on a scale from 1 to 5 in terms of overall impact.  This enables individual snowstorms to be placed in a historical context.   The NESIS is computed in the weeks following a snowstorm by NOAA.   NESIS categories range from 1, Notable, to 5, Extreme. 

The extremely early season Nor'easter of October 29-30 was determined to be a NESIS Category 1.   This score is based strictly on population and snowfall.  NESID does not provide an an assessment of infrastructure disruption, nor of societal disruption and hardship, as was generated by 3+ million power outages from downed tree limbs. 

In spite of being rated near the "bottom of the heap", in terms of all-time great snowstorms, what is remarkable is that no snowstorm in the NESIS Top 45 (Northeast urban corridor) has ever occurred earlier than December!   The large majority of historical snowstorms occur in January-February. 

Here is the official snow accumulation map from October 29-30 and the NESIS score as provided by NOAA:

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