The leading edge is just about to hit Harrisburg at 5pm. This just released from the NWS:

CECIL-HUNTERDON-WARREN-CARBON-MONROE-BERKS-WESTERN
CHESTER-NORTHAMPTON-WESTERN MONTGOMERY-EASTERN CHESTER-LEHIGH-UPPER
BUCKS-
433 PM EST TUE JAN 12 2016

…DANGEROUS SNOW SQUALLS WILL MOVE IN BY 6 PM EST…

* AT 430 PM EST…A SNOW SQUALL WAS MOVING THROUGH CENTRAL
PENNSYLVANIA. THIS SNOW SQUALL IS EXPECTED TO MOVE INTO
SOUTHEASTERN PENNSYLVANIA BY 6 PM EST.

* VISIBILITIES NEAR ONE QUARTER MILE AT TIMES WILL BE POSSIBLE.

* NEW SNOW ACCUMULATIONS OF AROUND ONE INCH WILL BE POSSIBLE. THIS
WILL LIKELY FALL IN LESS THAN ONE HOUR.

OCCASIONAL LIGHTNING IS ALSO POSSIBLE.

USE EXTRA CAUTION IF YOU MUST TRAVEL INTO OR THROUGH THIS DANGEROUS
SNOW SQUALL. RAPID CHANGES IN VISIBILITY AND POTENTIALLY SLICK ROADS
COULD LEAD TO ACCIDENTS. CONSIDER DELAYING TRAVEL UNTIL THE SQUALL
PASSES YOUR LOCATION.

A RAPID DROP IN TEMPERATURES WILL LEAD TO THE RAPID FORMATION OF
BLACK ICE ON AREA ROADWAYS. BLACK ICE IS NEARLY IMPOSSIBLE TO SEE
AND ROADWAYS MAY APPEAR WET. PLEASE USE EXTREME CAUTION…ESPECIALLY
ON BRIDGES…OVERPASSES AND AROUND CURVES. ALLOW PLENTY OF STOPPING
DISTANCE AND AVOID BRAKING SUDDENLY.