Today's weather related closure of the NYSE is an extremely rare event. In fact, in 127 years the market has only been closed for the whole day due to weather 6 times, and three of those times were on Saturdays (the exchanges were open on Saturdays up until 1952). There has only been one time, in 1888, that weather caused a multi-day closure. For reference, there have been roughly 30,000 trading days since 1885, which makes today a black swan of its own--a four sigma event.
Below is a list of all the times that the NYSE has ever been closed or partially closed due to weather.