Methodology for Developing a Heavy Wet Snow Scale for a Utility Company

Freezing rain has typically been the winter weather type that utility companies with an overhead electric infrastructure fear the most. However in recent years the Consolidated Edison Company of New York (Con Edison) has dealt with two major Northeast snow storms that have caused significant customer outages due to the density of the snow that fell. Neither storm had freezing rain, rather it was the weight of the snow accumulating on branches and power lines that caused power failures.

By February 25, 2010 1-3' of heavy wet snow had fallen across the Con Edison service territory. The greatest snow accumulations were in the company's northwestern territories outside of the NYC metropolitan area. Due to the complex nature of this storm and its multiple phases, in some places it had been snowing for almost 48 hours straight. This was the first snow only storm to cause significant customer outages in over 10 years. At the peak, 62,500 customers were without power.

Again on October 29, 2011 an unprecedented and unseasonable Nor'Easter left millions without power across the Northeast. Snow fall records in many cities across the Northeast were shattered thanks to this storm. At the peak Con Edison had 136,000 customers without power, the 3rd most impactful storm in the company's history.

While the company was prepared in advance both storms, forecasting the density of snow, and tracking the real time rain/snow line can be difficult for forecasters to pin down in advance. To be better prepared for the next heavy wet snow event Con Edison meteorologists developed new snow triggers to clearly communicate the potential impact from the next snow storm. This talk will provide an overview of each storm and provide some theories as to how the storm environment caused the snow to be so destructive. It will also describe the methodologies used to revise the company's storm preparedness matrix for heavy wet snow.