"Buffalo Lake Effect Snowstorm"
20 November 2000

On 20 November 2000, Buffalo, NY was hit with a lake effect snowstorm with strength unseen in several years, and disruptive force unequalled in nearly 25 years. Buffalo received 2 feet of snow in a relatively short time, with most falling in a 7-hour period. Frequent lightning occurred all afternoon with this snowfall, and the timing couldn't have been worse, as the brunt of the snowfall began around 2 p.m. local time. Many people tried to leave work early, but roads quickly became clogged with heavy traffic and between 2"-4" of snowfall per hour. Many people spent the night in autos, and buses full of school children were trapped, eventually spending the night in stores or makeshift shelters.

The conditions were prime for a heavy lake snowfall event, and the event was well forecast, though snowfall was underestimated. A deep layer of moist, unstable air was present on the morning of 20 November in Buffalo. The 1200Z BUF sounding illustrates this, and also shows the flow from the southwest to have little directional shear through a deep layer. Aloft, a strong shortwave trough with associated vorticity max sits just upstream at 1300Z 20 November, and remains upstream through about 2200Z when the trough axis passes to the east. Also, much of the cloud layer had temperatures that were favorable for snow crystal growth.

The snow fell early on in showers, as the cold front passed through. At 1317Z, Buffalo is under an area of heavy show showers, as indicated by radar. As the conditions came together, the snow began to concentrate in a narrow band. Here at 1701Z, the formation of the band can be identified. Snow fell in this way for many hours, with heavier embedded "thunder snow" pockets. Here at 0136Z 21 November, the snowband is still present, and has shifted south, though Buffalo is still on the north edge of the precipitation. After 0000Z 21 November, the winds began veering and took on a more westerly flow. This slowly moved the snowband south, and eventually changed the shape of the area of precipitation. Though the heavy snowfall would be over for Buffalo for the time being, other areas continued to receive snow for 2 days, with many areas picking up 1'-2' of snowfall.

The heavy snowfall over Erie County on 20 November 2000 fell over a very concentrated area. The 12"+ amounts fell in a strip less than 10 miles wide, and the area of 24" was concentrated in a strip about 3 miles wide. The coverage was such that only 10% of Erie County received snowfall, but nearly 80% of the population was affected by the snow. This case is an excellent example of a severe lake effect storm, exhibiting classic characteristics and critical timing, which allowed it to paralyze a city of over 1 million people.

Case Study 032