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    Why Did Philadelphia Get More Snow Sunday Than Last Winter?

    By By Alex Sosnowski, expert senior meteorologist.
    December 12, 2013, 12:43:17 AM EST

    Philadelphia International Airport received more snow (8.6 inches) from a single storm this past Sunday than it did all of last winter, when 8.3 inches fell.

    Mother nature pulled out all the stops with heavy snow in a narrow zone centered near the Mason-Dixon Line Sunday.

    The heavy snow quickly covered roadways, caused flight delays and cancellations, and contributed to many accidents.

    @lmontanad tweeted: "A WHITEOUT in #Philadelphia. #Eagles vs #Lions played during a blinding snow storm with more than 6 inches in the field."

    Additional Relevant Tweets and Social Media Reaction

    The mechanics and variables behind the snow debacle are complex and numerous. A simple explanation is offered in this story.

    According to Brian Wimer, AccuWeather winter weather expert, "For starters, a layer of fresh cold air moved in near the surface Saturday night over the mid-Atlantic and shortly thereafter a weak storm moved northeastward into that fresh cold air."

    While the storm was weak, there was plenty of warm, moist air to the south waiting to be tapped.

    "The weak storm allowed a warm front to set up several thousand feet above the ground which caused the air to rapidly rise and cool in an unusually narrow zone rather than be spread out over hundreds of square miles," Wimer said.


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    The band of heavy snow focused from parts of West Virginia to northern Virginia, northern Maryland, southern Pennsylvania, northern Delaware and southern New Jersey, including the Wilmington, Del., and Philadelphia metro areas. At times, the snow fell at the rate of 1 to 3 inches per hour.

    As a result, many areas exceeded their original prediction of snow in a little over an hour. The liquid amount from the snow around Philadelphia was a factor of 20 lower, so that 1 inch of snow was only about 0.05 of an inch of water or rain.

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    The band of snow could have just as easily set up farther south or north compared to where it did. Instead, it occurred in the vicinity of the Mason-Dixon Line.

    According to AccuWeather.com Expert Senior Meteorologist Henry Margusity, "Horizontal winds were very light from around 5,000 to 10,000 feet up, near where the snowflakes were rapidly forming and growing most vigorously."

    These light winds allowed the snowflakes to become very large and not be blown apart.


    650x366_12091538_snowflakeformation


    There are probably a couple of dozen of potential events similar to this past Sunday but in reality they only occur a handful of times over nation during a typical winter. Figuring out exactly where they will first set up and expand to prior to their occurrence is very challenging.

    Snowfall From the Sunday to Monday Storm (As of Midday Monday)

    City
    Amount (Inches)
    Philadelphia (Airport)
    8.6
    Wilmington, Del.
    8.5
    Philadelphia (City)
    5.5
    Baltimore (City)
    4.0
    Harrisburg, Pa.
    1.8
    Baltimore (Airport)
    1.6
    Pittsburgh
    1.1
    Washington, D.C.
    0.6
    Boston
    0.4
    Hartford, Conn.
    0.3
    Providence, R.I.
    0.3
    New York
    0.4

    Another storm will affect part of the Northeast Tuesday. For many areas along the I-95 corridor, there may be enough to shovel and plow.

    Most areas will receive between 1 and 3 inches of snow from the new storm Tuesday, spread out over a six- to eight-hour period. A narrow swath of 3 to 6 inches of snow will fall, including in some of the major I-95 cities.


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