A large high pressure system over nearby Canada and a low pressure system that passed south of the region set the stage for a protracted winter storm for northwest New Jersey and a winter weather event for Mercer and Somerset Counties. Precipitation began as light snow during the evening of the 2nd in the higher terrain of far northwest New Jersey and a mixture of light snow, light rain and light freezing drizzle elsewhere. Precipitation changed exclusively to light sleet and light freezing rain over Mercer and Somerset Counties and parts of Hunterdon County before sunrise on the 3rd. Steadier precipitation moved into the region around daybreak on the 3rd. By then warmer air aloft caused precipitation to fall as mainly freezing rain and sleet. Only in Sussex County did precipitation fall mainly as light snow. Eventually enough warm air moved in near the surface for precipitation to change to plain rain in Mercer and Somerset Counties and parts of Hunterdon, Warren and Morris Counties before Noon EST on the 3rd. Ice accretions were generally one tenth of an inch or less. In Sussex County, precipitation continued to fall as snow during heavier precipitation bursts and mixed with freezing rain and sleet at other times. As the low pressure system moved farther offshore and the winds shifted to the north, precipitation changed to all snow in Sussex County during the late afternoon of the 3rd and fell heavy at times that night. In Warren, Morris, Somerset and Hunterdon Counties precipitation reversed itself and went from a freezing rain and light rain mixture to sleet and then snow during the evening of the 3rd. The snow ended before daybreak on the 4th. Across Warren, Hunterdon and Morris Counties, total ice accretions averaged between one quarter and three-eighths of an inch. In addition one to three inches of snow accumulated on top of the ice. In Sussex County, ice accretions were generally less than one-quarter of an inch, but snow accumulations reached between 6 and 12 inches. It did not take long for traffic problems to begin once the freezing precipitation started on the second.  In Morris County, scores of vehicles were spinning out of control. Spin outs and minor accidents were common on Interstate 287. New Jersey State Route 10 in Denville was at a standstill for more than one hour as vehicles could not get up the hill. Mount Olive Police reported 25 accidents as both U.S. Routes 206 and 46 were closed in the township. Many accidents were also reported along Interstate 80 in Warren County and within Byram Township (Sussex County). Vehicles skidded into poles, guard rails and ditches. On the third, several school districts were closed in Morris and Hunterdon Counties. Schools had delayed openings in Somerset County. Many extracurricular activities were canceled. Scores of accidents occurred throughout this event in Sussex County. During the evening of the third as precipitation went from rain to freezing rain, many additional accidents occurred. In Somerset County, there were 65 collisions on Interstates 287 and 78 and Route 440.  In Morris County, there were forty accidents on Interstates 80 and 287.Specific accumulations included 12 inches in Wantage and Vernon (Sussex County), 11.9 inches in Barry Lakes (Sussex County), 6.2 inches in Newton (Sussex County), 4 inches in Netcong (Morris County),  3 inches in Hope and Belvidere (both Warren County), 2 inches in Long Valley (Morris County), 1.1 inches in Chatham (Morris County) and 1 inch in Flemington (Hunterdon County). The low pressure system responsible for the wintry weather developed in the Southern Plains on January 1st and moved into the Tennessee Valley during the morning of the 2nd. By the morning of the 3rd, it moved into North Carolina where a secondary formed near Norfolk, Virginia. The low then moved northeast and passed just to the south of Cape Cod during the morning of the 4th. While this low passed south of the area, a high pressure system remained nearly stationary over nearby Canada and provided and helped entrench cold air near the surface. This causes precipitation to fall as freezing rain even though it was warm enough aloft for the falling snow to change to plain rain.

Winter Weather in SOMERSET, NEW JERSEY
From 03-JAN-03 19:00:00 to 04-JAN-03 03:00:00 (EST)
Reported by: TRAINED SPOTTER

Winter Storm in WARREN, NEW JERSEY
From 02-JAN-03 20:00:00 to 04-JAN-03 06:00:00 (EST)
Reported by: TRAINED SPOTTER

Winter Weather in MERCER, NEW JERSEY
From 02-JAN-03 22:30:00 to 03-JAN-03 09:00:00 (EST)
Reported by: TRAINED SPOTTER

Winter Weather in SOMERSET, NEW JERSEY
From 02-JAN-03 22:30:00 to 03-JAN-03 11:00:00 (EST)
Reported by: TRAINED SPOTTER

Winter Storm in SUSSEX, NEW JERSEY
From 02-JAN-03 19:00:00 to 04-JAN-03 06:00:00 (EST)
Reported by: TRAINED SPOTTER

Winter Storm in HUNTERDON, NEW JERSEY
From 02-JAN-03 20:00:00 to 04-JAN-03 06:00:00 (EST)
Reported by: TRAINED SPOTTER

Winter Storm in MORRIS, NEW JERSEY
From 02-JAN-03 20:00:00 to 04-JAN-03 06:00:00 (EST)
Reported by: TRAINED SPOTTER