Snowfall in March is not uncommon. The last year without at least a trace of snowfall in March was in 2000...and it promptly snowed in April that year. We've seen trace amounts in many years but other years we've picked up a bit more than that.
The record for most snowfall in a given March is 15.2", set back in 1914, with four distinct snowfalls contributing to that total, none of which were larger than six inches. We've exceeded ten inches in the month for snowfall ten times since 1884, last of those being in 1993 (Superstorm). The Superstorm is also Philadelphia's largest March snowfall on record, with 12" of snow (and sleet) falling.
We've had three snowfalls of ten inches or more in the month of March -- last of those being in 1993.
The 1958 snowstorm brought 11.4" over three days to Philadelphia but brought fifty inches of snow to Morgantown. The storm was a prodigious snowfall producer to hilly and mountainous areas as the Poconos picked up close to three feet in that storm, while the city "just" got 11.4". The 1888 storm was even worse for New York and Southern New England than it was for Philadelphia but the city still picked up 10.5" of snow from the storm.
Our last "big" snowfall in March was in 2009 -- we picked up nine inches at the Airport on the 1st and 2nd with a storm system that brought most of its snow in four to six hours in the evening. Intensity of snowfall was a huge driver of accumulation as many locations struggled to accumulate much snowfall during the day.