|Blizzard of February 2013.|
The word from Notify NYC is that 6-8 inches of snow will fall starting 6 pm tomorrow, January 2, through 1 am Friday. The snow will be accompanied by "low temperatures" which means that the snow will accumulate and some will turn to ice.
Expect salt spreaders. Last year on February 7-9, the first big blizzard of the winter hit New York City and then-Mayor Bloomberg reported he had on hand 250,000 tons to spread on the streets of New York.
A snowstorm happening at the end of a week, on Friday or Saturday, is relatively benign for offices because only one day of work is lost. By Monday the commute is likely to be back to normal. Saturday is a less crucial day for most businesses, obviously excluding retailers and entertainments. During my stint as chief economist for three NYC Comptrollers in 1992-2006, we considered a Saturday economy as three-fourths of a Monday-Friday weekday economy and Sunday was one-fourth of a weekday, so it added up to a six-weekday week.
We estimated the relationship between certain storm variables and economic impact based on historical records. The crucial variables in a snowstorm for determining economic impact are the timing, the precipitation and the temperature. The impact is reduced if the snow is on a weekend, if the precipitation is low (two inches is where trouble can start) and if the temperature is above freezing, 32 F (32 degrees Fahrenheit).
Putting down salt allows the City of New York to reduce the impact of freezing temperature on the ability of commuters to get to work, or shoppers to get to stores. One of the worst scenarios is a slushy snowfall and then a deep freeze, causing icy roads. A snowstorm becomes a blizzard if the snow is driven by the wind.
In the laboratory, adding salt (sodium chloride) to water can bring down the freezing-melting point – depending on which way one is going - from 32 degrees Fahrenheit to 20 F (in the case of a 10 percent concentration of salt) or 2 F (for a 20 percent concentration). In practice, the lower number depends on how much salt one puts down on the roads (the more salt that is added, the higher the salinity percentage and the lower the freezing point of the water). In a lab, the freezing point can be brought down lower than in storm conditions. One source suggests that below 15 F, salt will have little effect.
So salt is only useful to add when the temperature is between 15 F and 32 F. Below 15 F, the salt won’t melt the ice. Above 32 F, ice won't form and the salinized water will just run off into the city sewers.
The preferred remedy for ice in places like Montreal, where I spent much of my childhood, is sand, which helps provide traction to pedestrians and motorists regardless of the temperature. My beloved grandmother Olga van Stockum nonetheless died of hip injuries after falling on Montreal ice in 1949.
Salt has some negative effects on the environment. It corrodes cars and other vehicles and the roads themselves. It is bad for shoes. The runoff is terrible for plants and marine life. Pets that walk outside get the salt on their paws and suffer from the abrasion.
But a big city needs to keep working. So we accept the negative impact of salt. The test is whether the mayor can keep the roads open on Friday morning.