Happy Anniversary!

Asheville, NC, March 14, 1993.  Source: NOAA

This week marks the 20th anniversary of the 1993 Superstorm, one of the biggest snowstorms ever in the eastern United States and a seminal moment in modern weather forecasting.

As summarized in the now classic paper by Kocin et al. (1995), the Superstorm began as disorganized low over the Gulf of Mexico, but deepened 17 mb in 12 hours to reach 984 mb when it was just south of Louisiana.  As it moved up the eastern seaboard, the central pressure dropped to 971 mb over Georgia and 960 mb over Delaware.  The storm set record low sea level pressures at locations spanning from Georgia to Maine.

Source: Kocin et al. (1995)

Measurable snow stretched from the Florida Panhandle into southeast Canada, covering an area containing 90 million inhabitants in the eastern U.S.  Accumulations of more than 40 inches were observed at locations in Maryland, New York, North Carolina, Pennsylvania, Tennessee, Vermont, and Wast Virginia.  The big winners were Mt Mitchell, North Carolina (50 inches) and Mt. Laconte, Tennessee (60 inches).

Source: Kocin et al. (1995)

Kocin and Uccellini (2004) show that the area and population affected by a snowfall of 10 inches or more was likely the largest of any east coast storm during the historical record.  The storm was the highest rated of any since 1888 on their Northeast Snowfall Impact Scale (NESIS) and one of two (the other is the January Blizzard of 1996) classified as category 5 for extreme (see also this NCDC web site).

Prior to the Superstorm, forecasts for nor'easters were not known for their reliability.  As a budding young skier in the northeast, I recall many surprise storms and great forecast disappointments.  Storms such as the 1979 President's Day Cyclone, which produced the largest snowfall accumulation in Washington D.C. in 50 years, were poorly forecast by the numerical models of the day (e.g., Uccellini et al. 1984).

By 1993, however, the resolution and capability of numerical models had reached a point where they were becoming more skillful at predicting nor'easters and forecasters were able to process and take maximum advantage of these forecasts.  The forecasts for the Superstorm were especially noteworthy.  As summarized by Uccellini et al. (1995), the Superstorm cyclogenesis was predicted up to 5 days in advance, the unusual intensity of the storm 3 days in advance, and the excessive snowfall amounts and coverage two days advance.   It was a major forecast victory.

Headline from the Boston Herald prior to the Superstorm.
Source: Uccellini et al. (1995)

Over the two decades since the Superstorm, winter storm forecasts along the east coast have continued to improve.  However, there is still work to do, as illustrated by the recent "Snowquester" forecast in Washington DC (see Capital Weather Gang and Cliff Mass Blog posts).  Nevertheless, I'm proud of what the profession has accomplished the past two decades and excited about where we can go in the future.