Final Thoughts



The small snowfall in Raleigh NC on 19 January 2005 will be long remembered for the unprecedented high impact it had on the local community. It is an event with as many sociological implications as meteorological.



Regarding the meteorological implications, the forecast calling for only a trace of snow to no more than a dusting (i.e., less than an inch) was correct for 22 of the 32 counties in Central North Carolina. The sudden increase in aerial coverage and intensity of the light snow as it quickly moved across the Raleigh area and points just to the north and east can be explained after the fact; however, consistently and accurately forecasting such a small scale (i.e., across several counties) change well in advance is still beyond the state of the science.



Forecasters were certainly well aware of the relatively high liquid equivalent to snow ratios associated with a northwest flow driven event, and they intuitively knew that cold ground and road surfaces would not contribute to melting. Still a number of factors had to come together to produce 8 hours of gridlock from so little snowfall. Chief among them was the occasional bursts of moderate snow. Though the bursts occurred only several times during the 2.5 hour snowfall period, they did feature larger flakes which efficiently coated the roads. During the period of light snow, the very small and dry flakes had simply been blowing across the roads. Once the snow was on the roads, the impact of heavy traffic was realized. Vehicles clogging the primary roads in a mass exodus of the city compacted the light coating into an icy composition which lead to numerous accidents and more gridlock.



Perhaps, the bottom line for forecasters is that a marginal snow event such as this one, calls for more than meteorological considerations. If factors are combining to present a threat of high impact from even a small amount of snow, then additional consideration can be given to issuing a forecast that accounts for that potential. Those factors include light snow with occasional moderate bursts moving across a large metropolitan area during the afternoon of a business day, preceded by very cold temperatures, and associated with a northwest flow driven event where liquid equivalent to snow ratios can be high. The only ingredient needed to again turn a ½ - 1 inch snowfall into traffic gridlock is the human response to the fallen snow.



