when as much as eight inches of snow fell in Monmouth County, NJ, and as much as five inches of snow fell in Upper Montgomery County.
The cause of the April 7th, 2003 snowfall was a weak impulse working northeast from the southern Mid Atlantic, up the East Coast, into a cold high over Quebec. The high pushed colder air into the Delaware Valley that, when interacting with the precipitation as it moved into the region, allowed for temperatures to cool further and see snow at the onset as precipitation moved in during the early morning hours.
This event was not all snow for everyone -- Philadelphia did change over to drizzle and light rain in the afternoon as a modest amount of milder air worked in aloft and allowed precipitation to change over at the Airport. However, farther north and northwest snow was the end game for many.
Philadelphia picked up 1.8" of snow from this event -- the last time the city has picked up an inch of snow in an April snow event.
April snowfalls have generally been modest through the city's history -- only three times in the last 50 years the city has picked up more than three inches in any single event -- 1965, 1971, and 1982. The most snow that has accumulated in a singular April storm was waaaaayyyyyyyyyy back on April 3rd-4th, 1915. 19.4" of snow fell in Philadelphia, with as much as a foot of snow in portions of North Carolina and ten or more inches falling in parts of the Delmarva from a rare coastal nor'easter. The April 1915 storm is the only foot plus April snow on record and one of only three six inch storms in the month to hit the city, with no storm bringing a half foot to the city since 1924.
Even the "Blizzard of '82" that hit New York and New England in early April only brought Philadelphia 3.5" of snow and the April Fools Storm of 1997 dropped a modest 1.6" in the city (much more fell over the Poconos and North Jersey hills though)...however, nothing comes close to 1915 in terms of wintry production in April although you will get the occasional reminder that winter can rear its head once or twice in a month that is known more for showers to bring forth flowers than snows.